(function(global_object) {
  "use strict";

  // @note
  //   A few conventions for the documentation of this file:
  //   1. Always use "//" (in contrast with "/**/")
  //   2. The syntax used is Yardoc (yardoc.org), which is intended for Ruby (se below)
  //   3. `@param` and `@return` types should be preceded by `JS.` when referring to
  //      JavaScript constructors (e.g. `JS.Function`) otherwise Ruby is assumed.
  //   4. `nil` and `null` being unambiguous refer to the respective
  //      objects/values in Ruby and JavaScript
  //   5. This is still WIP :) so please give feedback and suggestions on how
  //      to improve or for alternative solutions
  //
  //   The way the code is digested before going through Yardoc is a secret kept
  //   in the docs repo (https://github.com/opal/docs/tree/master).

  var console;

  // Detect the global object
  if (typeof(globalThis) !== 'undefined') { global_object = globalThis; }
  else if (typeof(global) !== 'undefined') { global_object = global; }
  else if (typeof(window) !== 'undefined') { global_object = window; }

  // Setup a dummy console object if missing
  if (global_object.console == null) {
    global_object.console = {};
  }

  if (typeof(global_object.console) === 'object') {
    console = global_object.console;
  } else {
    console = {};
  }

  if (!('log' in console)) { console.log = function () {}; }
  if (!('warn' in console)) { console.warn = console.log; }

  if (typeof(global_object.Opal) !== 'undefined') {
    console.warn('Opal already loaded. Loading twice can cause troubles, please fix your setup.');
    return global_object.Opal;
  }

  var nil;

  // The actual class for BasicObject
  var BasicObject;

  // The actual Object class.
  // The leading underscore is to avoid confusion with window.Object()
  var _Object;

  // The actual Module class
  var Module;

  // The actual Class class
  var Class;

  // The Opal.Opal class (helpers etc.)
  var _Opal;

  // The Kernel module
  var Kernel;

  // The Opal object that is exposed globally
  var Opal = global_object.Opal = {};

  // This is a useful reference to global object inside ruby files
  Opal.global = global_object;

  // Configure runtime behavior with regards to require and unsupported features
  Opal.config = {
    missing_require_severity: 'error',        // error, warning, ignore
    unsupported_features_severity: 'warning', // error, warning, ignore
    experimental_features_severity: 'warning',// warning, ignore
    enable_stack_trace: true                  // true, false
  };

  // Minify common function calls
  var $call      = Function.prototype.call;
  var $bind      = Function.prototype.bind;
  var $has_own   = Object.hasOwn || $call.bind(Object.prototype.hasOwnProperty);
  var $set_proto = Object.setPrototypeOf;
  var $slice     = $call.bind(Array.prototype.slice);
  var $splice    = $call.bind(Array.prototype.splice);

  // Nil object id is always 4
  var nil_id = 4;

  // Generates even sequential numbers greater than 4
  // (nil_id) to serve as unique ids for ruby objects
  var unique_id = nil_id;

  // Return next unique id
  function $uid() {
    unique_id += 2;
    return unique_id;
  };
  Opal.uid = $uid;

  // Retrieve or assign the id of an object
  Opal.id = function(obj) {
    if (obj.$$is_number) return (obj * 2)+1;
    if (obj.$$id == null) {
      $prop(obj, '$$id', $uid());
    }
    return obj.$$id;
  };

  // Globals table
  var $gvars = Opal.gvars = {};

  // Exit function, this should be replaced by platform specific implementation
  // (See nodejs and chrome for examples)
  Opal.exit = function(status) { if ($gvars.DEBUG) console.log('Exited with status '+status); };

  // keeps track of exceptions for $!
  Opal.exceptions = [];

  // @private
  // Pops an exception from the stack and updates `$!`.
  Opal.pop_exception = function(rescued_exception) {
    var exception = Opal.exceptions.pop();
    if (exception === rescued_exception) {
      // Current $! is raised in the rescue block, so we don't update it
    }
    else if (exception) {
      $gvars["!"] = exception;
    }
    else {
      $gvars["!"] = nil;
    }
  };

  // A helper function for raising things, that gracefully degrades if necessary
  // functionality is not yet loaded.
  function $raise(klass, message) {
    // Raise Exception, so we can know that something wrong is going on.
    if (!klass) klass = Opal.Exception || Error;

    if (Kernel && Kernel.$raise) {
      if (arguments.length > 2) {
        Kernel.$raise(klass.$new.apply(klass, $slice(arguments, 1)));
      }
      else {
        Kernel.$raise(klass, message);
      }
    }
    else if (!klass.$new) {
      throw new klass(message);
    }
    else {
      throw klass.$new(message);
    }
  }

  // Reuse the same object for performance/memory sake
  var prop_options = {
    value: undefined,
    enumerable: false,
    configurable: true,
    writable: true
  };

  function $prop(object, name, initialValue) {
    if (typeof(object) === "string") {
      // Special case for:
      //   s = "string"
      //   def s.m; end
      // String class is the only class that:
      // + compiles to JS primitive
      // + allows method definition directly on instances
      // numbers, true, false and null do not support it.
      object[name] = initialValue;
    } else {
      prop_options.value = initialValue;
      Object.defineProperty(object, name, prop_options);
    }
  }

  Opal.prop = $prop;

  // @deprecated
  Opal.defineProperty = Opal.prop;

  Opal.slice = $slice;

  // Helpers
  // -----

  var $truthy = Opal.truthy = function(val) {
    return false !== val && nil !== val && undefined !== val && null !== val && (!(val instanceof Boolean) || true === val.valueOf());
  };

  Opal.falsy = function(val) {
    return !$truthy(val);
  };

  Opal.type_error = function(object, type, method, coerced) {
    object = object.$$class;

    if (coerced && method) {
      coerced = coerced.$$class;
      $raise(Opal.TypeError,
        "can't convert " + object + " into " + type +
        " (" + object + "#" + method + " gives " + coerced + ")"
      )
    } else {
      $raise(Opal.TypeError,
        "no implicit conversion of " + object + " into " + type
      )
    }
  };

  Opal.coerce_to = function(object, type, method, args) {
    var body;

    if (method === 'to_int' && type === Opal.Integer && object.$$is_number)
      return object < 0 ? Math.ceil(object) : Math.floor(object);

    if (method === 'to_str' && type === Opal.String && object.$$is_string)
      return object;

    if (Opal.is_a(object, type)) return object;

    // Fast path for the most common situation
    if (object['$respond_to?'].$$pristine && object.$method_missing.$$pristine) {
      body = object[$jsid(method)];
      if (body == null || body.$$stub) Opal.type_error(object, type);
      return body.apply(object, args);
    }

    if (!object['$respond_to?'](method)) {
      Opal.type_error(object, type);
    }

    if (args == null) args = [];
    return Opal.send(object, method, args);
  }

  Opal.respond_to = function(obj, jsid, include_all) {
    if (obj == null || !obj.$$class) return false;
    include_all = !!include_all;
    var body = obj[jsid];

    if (obj['$respond_to?'].$$pristine) {
      if (typeof(body) === "function" && !body.$$stub) {
        return true;
      }
      if (!obj['$respond_to_missing?'].$$pristine) {
        return Opal.send(obj, obj['$respond_to_missing?'], [jsid.substr(1), include_all]);
      }
    } else {
      return Opal.send(obj, obj['$respond_to?'], [jsid.substr(1), include_all]);
    }
  }

  // TracePoint support
  // ------------------
  //
  // Support for `TracePoint.trace(:class) do ... end`
  Opal.trace_class = false;
  Opal.tracers_for_class = [];

  function invoke_tracers_for_class(klass_or_module) {
    var i, ii, tracer;

    for(i = 0, ii = Opal.tracers_for_class.length; i < ii; i++) {
      tracer = Opal.tracers_for_class[i];
      tracer.trace_object = klass_or_module;
      tracer.block.$call(tracer);
    }
  }

  function handle_autoload(cref, name) {
    if (!cref.$$autoload[name].loaded) {
      cref.$$autoload[name].loaded = true;
      try {
        Opal.Kernel.$require(cref.$$autoload[name].path);
      } catch (e) {
        cref.$$autoload[name].exception = e;
        throw e;
      }
      cref.$$autoload[name].required = true;
      if (cref.$$const[name] != null) {
        cref.$$autoload[name].success = true;
        return cref.$$const[name];
      }
    } else if (cref.$$autoload[name].loaded && !cref.$$autoload[name].required) {
      if (cref.$$autoload[name].exception) { throw cref.$$autoload[name].exception; }
    }
  }

  // Constants
  // ---------
  //
  // For future reference:
  // - The Rails autoloading guide (http://guides.rubyonrails.org/v5.0/autoloading_and_reloading_constants.html)
  // - @ConradIrwin's 2012 post on “Everything you ever wanted to know about constant lookup in Ruby” (http://cirw.in/blog/constant-lookup.html)
  //
  // Legend of MRI concepts/names:
  // - constant reference (cref): the module/class that acts as a namespace
  // - nesting: the namespaces wrapping the current scope, e.g. nesting inside
  //            `module A; module B::C; end; end` is `[B::C, A]`

  // Get the constant in the scope of the current cref
  function const_get_name(cref, name) {
    if (cref) {
      if (cref.$$const[name] != null) { return cref.$$const[name]; }
      if (cref.$$autoload && cref.$$autoload[name]) {
        return handle_autoload(cref, name);
      }
    }
  }

  // Walk up the nesting array looking for the constant
  function const_lookup_nesting(nesting, name) {
    var i, ii, constant;

    if (nesting.length === 0) return;

    // If the nesting is not empty the constant is looked up in its elements
    // and in order. The ancestors of those elements are ignored.
    for (i = 0, ii = nesting.length; i < ii; i++) {
      constant = nesting[i].$$const[name];
      if (constant != null) {
        return constant;
      } else if (nesting[i].$$autoload && nesting[i].$$autoload[name]) {
        return handle_autoload(nesting[i], name);
      }
    }
  }

  // Walk up the ancestors chain looking for the constant
  function const_lookup_ancestors(cref, name) {
    var i, ii, ancestors;

    if (cref == null) return;

    ancestors = $ancestors(cref);

    for (i = 0, ii = ancestors.length; i < ii; i++) {
      if (ancestors[i].$$const && $has_own(ancestors[i].$$const, name)) {
        return ancestors[i].$$const[name];
      } else if (ancestors[i].$$autoload && ancestors[i].$$autoload[name]) {
        return handle_autoload(ancestors[i], name);
      }
    }
  }

  // Walk up Object's ancestors chain looking for the constant,
  // but only if cref is missing or a module.
  function const_lookup_Object(cref, name) {
    if (cref == null || cref.$$is_module) {
      return const_lookup_ancestors(_Object, name);
    }
  }

  // Call const_missing if nothing else worked
  function const_missing(cref, name) {
    return (cref || _Object).$const_missing(name);
  }

  // Look for the constant just in the current cref or call `#const_missing`
  Opal.const_get_local = function(cref, name, skip_missing) {
    var result;

    if (cref == null) return;

    if (cref === '::') cref = _Object;

    if (!cref.$$is_module && !cref.$$is_class) {
      $raise(Opal.TypeError, cref.toString() + " is not a class/module");
    }

    result = const_get_name(cref, name);
    return result != null || skip_missing ? result : const_missing(cref, name);
  };

  // Look for the constant relative to a cref or call `#const_missing` (when the
  // constant is prefixed by `::`).
  Opal.const_get_qualified = function(cref, name, skip_missing) {
    var result, cache, cached, current_version = Opal.const_cache_version;

    if (name == null) {
      // A shortpath for calls like ::String => $$$("String")
      result = const_get_name(_Object, cref);

      if (result != null) return result;
      return Opal.const_get_qualified(_Object, cref, skip_missing);
    }

    if (cref == null) return;

    if (cref === '::') cref = _Object;

    if (!cref.$$is_module && !cref.$$is_class) {
      $raise(Opal.TypeError, cref.toString() + " is not a class/module");
    }

    if ((cache = cref.$$const_cache) == null) {
      $prop(cref, '$$const_cache', Object.create(null));
      cache = cref.$$const_cache;
    }
    cached = cache[name];

    if (cached == null || cached[0] !== current_version) {
      ((result = const_get_name(cref, name))              != null) ||
      ((result = const_lookup_ancestors(cref, name))      != null);
      cache[name] = [current_version, result];
    } else {
      result = cached[1];
    }

    return result != null || skip_missing ? result : const_missing(cref, name);
  };

  // Initialize the top level constant cache generation counter
  Opal.const_cache_version = 1;

  // Look for the constant in the open using the current nesting and the nearest
  // cref ancestors or call `#const_missing` (when the constant has no :: prefix).
  Opal.const_get_relative = function(nesting, name, skip_missing) {
    var cref = nesting[0], result, current_version = Opal.const_cache_version, cache, cached;

    if ((cache = nesting.$$const_cache) == null) {
      $prop(nesting, '$$const_cache', Object.create(null));
      cache = nesting.$$const_cache;
    }
    cached = cache[name];

    if (cached == null || cached[0] !== current_version) {
      ((result = const_get_name(cref, name))              != null) ||
      ((result = const_lookup_nesting(nesting, name))     != null) ||
      ((result = const_lookup_ancestors(cref, name))      != null) ||
      ((result = const_lookup_Object(cref, name))         != null);

      cache[name] = [current_version, result];
    } else {
      result = cached[1];
    }

    return result != null || skip_missing ? result : const_missing(cref, name);
  };

  // Register the constant on a cref and opportunistically set the name of
  // unnamed classes/modules.
  function $const_set(cref, name, value) {
    var new_const = true;

    if (cref == null || cref === '::') cref = _Object;

    if (value.$$is_a_module) {
      if (value.$$name == null || value.$$name === nil) value.$$name = name;
      if (value.$$base_module == null) value.$$base_module = cref;
    }

    cref.$$const = (cref.$$const || Object.create(null));

    if (name in cref.$$const || ("$$autoload" in cref && name in cref.$$autoload)) {
      new_const = false;
    }

    cref.$$const[name] = value;

    // Add a short helper to navigate constants manually.
    // @example
    //   Opal.$$.Regexp.$$.IGNORECASE
    cref.$$ = cref.$$const;

    Opal.const_cache_version++;

    // Expose top level constants onto the Opal object
    if (cref === _Object) Opal[name] = value;

    // Name new class directly onto current scope (Opal.Foo.Baz = klass)
    $prop(cref, name, value);

    if (new_const && cref.$const_added && !cref.$const_added.$$pristine) {
      cref.$const_added(name);
    }

    return value;
  };

  Opal.const_set = $const_set;

  // Get all the constants reachable from a given cref, by default will include
  // inherited constants.
  Opal.constants = function(cref, inherit) {
    if (inherit == null) inherit = true;

    var module, modules = [cref], i, ii, constants = {}, constant;

    if (inherit) modules = modules.concat($ancestors(cref));
    if (inherit && cref.$$is_module) modules = modules.concat([Opal.Object]).concat($ancestors(Opal.Object));

    for (i = 0, ii = modules.length; i < ii; i++) {
      module = modules[i];

      // Do not show Objects constants unless we're querying Object itself
      if (cref !== _Object && module == _Object) break;

      for (constant in module.$$const) {
        constants[constant] = true;
      }
      if (module.$$autoload) {
        for (constant in module.$$autoload) {
          constants[constant] = true;
        }
      }
    }

    return Object.keys(constants);
  };

  // Remove a constant from a cref.
  Opal.const_remove = function(cref, name) {
    Opal.const_cache_version++;

    if (cref.$$const[name] != null) {
      var old = cref.$$const[name];
      delete cref.$$const[name];
      return old;
    }

    if (cref.$$autoload && cref.$$autoload[name]) {
      delete cref.$$autoload[name];
      return nil;
    }

    $raise(Opal.NameError, "constant "+cref+"::"+cref.$name()+" not defined");
  };

  // Generates a function that is a curried const_get_relative.
  Opal.const_get_relative_factory = function(nesting) {
    return function(name, skip_missing) {
      return Opal.$$(nesting, name, skip_missing);
    }
  }

  // Setup some shortcuts to reduce compiled size
  Opal.$$ = Opal.const_get_relative;
  Opal.$$$ = Opal.const_get_qualified;
  Opal.$r = Opal.const_get_relative_factory;

  function descends_from_bridged_class(klass) {
    if (klass == null) return false;
    if (klass.$$bridge) return klass;
    if (klass.$$super) return descends_from_bridged_class(klass.$$super);
    return false;
  }

  // Modules & Classes
  // -----------------

  // A `class Foo; end` expression in ruby is compiled to call this runtime
  // method which either returns an existing class of the given name, or creates
  // a new class in the given `base` scope.
  //
  // If a constant with the given name exists, then we check to make sure that
  // it is a class and also that the superclasses match. If either of these
  // fail, then we raise a `TypeError`. Note, `superclass` may be null if one
  // was not specified in the ruby code.
  //
  // We pass a constructor to this method of the form `function ClassName() {}`
  // simply so that classes show up with nicely formatted names inside debuggers
  // in the web browser (or node/sprockets).
  //
  // The `scope` is the current `self` value where the class is being created
  // from. We use this to get the scope for where the class should be created.
  // If `scope` is an object (not a class/module), we simple get its class and
  // use that as the scope instead.
  //
  // @param scope        [Object] where the class is being created
  // @param superclass   [Class,null] superclass of the new class (may be null)
  // @param singleton    [Boolean,null] a true value denotes we want to allocate
  //                                    a singleton
  //
  // @return new [Class]  or existing ruby class
  //
  function $allocate_class(name, superclass, singleton) {
    var klass, bridged_descendant;

    if (bridged_descendant = descends_from_bridged_class(superclass)) {
      // Inheritance from bridged classes requires
      // calling original JS constructors
      klass = function() {
        var self = new ($bind.apply(bridged_descendant.$$constructor, $prepend(null, arguments)))();

        // and replacing a __proto__ manually
        $set_proto(self, klass.$$prototype);
        return self;
      }
    } else {
      klass = function(){};
    }

    if (name && name !== nil) {
      $prop(klass, 'displayName', '::'+name);
    }

    $prop(klass, '$$name', name);
    $prop(klass, '$$constructor', klass);
    $prop(klass, '$$prototype', klass.prototype);
    $prop(klass, '$$const', {});
    $prop(klass, '$$is_class', true);
    $prop(klass, '$$is_a_module', true);
    $prop(klass, '$$super', superclass);
    $prop(klass, '$$cvars', {});
    $prop(klass, '$$own_included_modules', []);
    $prop(klass, '$$own_prepended_modules', []);
    $prop(klass, '$$ancestors', []);
    $prop(klass, '$$ancestors_cache_version', null);
    $prop(klass, '$$subclasses', []);
    $prop(klass, '$$cloned_from', []);

    $prop(klass.$$prototype, '$$class', klass);

    // By default if there are no singleton class methods
    // __proto__ is Class.prototype
    // Later singleton methods generate a singleton_class
    // and inject it into ancestors chain
    if (Opal.Class) {
      $set_proto(klass, Opal.Class.prototype);
    }

    if (superclass != null) {
      $set_proto(klass.$$prototype, superclass.$$prototype);

      if (singleton !== true) {
        // Let's not forbid GC from cleaning up our
        // subclasses.
        if (typeof WeakRef !== 'undefined') {
          // First, let's clean up our array from empty objects.
          var i, subclass, rebuilt_subclasses = [];
          for (i = 0; i < superclass.$$subclasses.length; i++) {
            subclass = superclass.$$subclasses[i];
            if (subclass.deref() !== undefined) {
              rebuilt_subclasses.push(subclass);
            }
          }
          // Now, let's add our class.
          rebuilt_subclasses.push(new WeakRef(klass));
          superclass.$$subclasses = rebuilt_subclasses;
        }
        else {
          superclass.$$subclasses.push(klass);
        }
      }

      if (superclass.$$meta) {
        // If superclass has metaclass then we have explicitely inherit it.
        Opal.build_class_singleton_class(klass);
      }
    }

    return klass;
  };
  Opal.allocate_class = $allocate_class;


  function find_existing_class(scope, name) {
    // Try to find the class in the current scope
    var klass = const_get_name(scope, name);

    // If the class exists in the scope, then we must use that
    if (klass) {
      // Make sure the existing constant is a class, or raise error
      if (!klass.$$is_class) {
        $raise(Opal.TypeError, name + " is not a class");
      }

      return klass;
    }
  }

  function ensureSuperclassMatch(klass, superclass) {
    if (klass.$$super !== superclass) {
      $raise(Opal.TypeError, "superclass mismatch for class " + klass.$$name);
    }
  }

  Opal.klass = function(scope, superclass, name) {
    var bridged;

    if (scope == null || scope == '::') {
      // Global scope
      scope = _Object;
    } else if (!scope.$$is_class && !scope.$$is_module) {
      // Scope is an object, use its class
      scope = scope.$$class;
    }

    // If the superclass is not an Opal-generated class then we're bridging a native JS class
    if (
      superclass != null && (!superclass.hasOwnProperty || (
        superclass.hasOwnProperty && !superclass.hasOwnProperty('$$is_class')
      ))
    ) {
      if (superclass.constructor && superclass.constructor.name == "Function") {
        bridged = superclass;
        superclass = _Object;
      } else {
        $raise(Opal.TypeError, "superclass must be a Class (" + (
          (superclass.constructor && (superclass.constructor.name || superclass.constructor.$$name)) ||
          typeof(superclass)
        ) + " given)");
      }
    }

    var klass = find_existing_class(scope, name);

    if (klass != null) {
      if (superclass) {
        // Make sure existing class has same superclass
        ensureSuperclassMatch(klass, superclass);
      }
    }
    else {
      // Class doesn't exist, create a new one with given superclass...

      // Not specifying a superclass means we can assume it to be Object
      if (superclass == null) {
        superclass = _Object;
      }

      // Create the class object (instance of Class)
      klass = $allocate_class(name, superclass);
      $const_set(scope, name, klass);

      // Call .inherited() hook with new class on the superclass
      if (superclass.$inherited) {
        superclass.$inherited(klass);
      }

      if (bridged) {
        Opal.bridge(bridged, klass);
      }
    }

    if (Opal.trace_class) { invoke_tracers_for_class(klass); }

    return klass;
  };

  // Define new module (or return existing module). The given `scope` is basically
  // the current `self` value the `module` statement was defined in. If this is
  // a ruby module or class, then it is used, otherwise if the scope is a ruby
  // object then that objects real ruby class is used (e.g. if the scope is the
  // main object, then the top level `Object` class is used as the scope).
  //
  // If a module of the given name is already defined in the scope, then that
  // instance is just returned.
  //
  // If there is a class of the given name in the scope, then an error is
  // generated instead (cannot have a class and module of same name in same scope).
  //
  // Otherwise, a new module is created in the scope with the given name, and that
  // new instance is returned back (to be referenced at runtime).
  //
  // @param  scope [Module, Class] class or module this definition is inside
  // @param  id   [String] the name of the new (or existing) module
  //
  // @return [Module]
  function $allocate_module(name) {
    var constructor = function(){};
    var module = constructor;

    if (name)
      $prop(constructor, 'displayName', name+'.constructor');

    $prop(module, '$$name', name);
    $prop(module, '$$prototype', constructor.prototype);
    $prop(module, '$$const', {});
    $prop(module, '$$is_module', true);
    $prop(module, '$$is_a_module', true);
    $prop(module, '$$cvars', {});
    $prop(module, '$$iclasses', []);
    $prop(module, '$$own_included_modules', []);
    $prop(module, '$$own_prepended_modules', []);
    $prop(module, '$$ancestors', [module]);
    $prop(module, '$$ancestors_cache_version', null);
    $prop(module, '$$cloned_from', []);

    $set_proto(module, Opal.Module.prototype);

    return module;
  };
  Opal.allocate_module = $allocate_module;

  function find_existing_module(scope, name) {
    var module = const_get_name(scope, name);
    if (module == null && scope === _Object) module = const_lookup_ancestors(_Object, name);

    if (module) {
      if (!module.$$is_module && module !== _Object) {
        $raise(Opal.TypeError, name + " is not a module");
      }
    }

    return module;
  }

  Opal.module = function(scope, name) {
    var module;

    if (scope == null || scope == '::') {
      // Global scope
      scope = _Object;
    } else if (!scope.$$is_class && !scope.$$is_module) {
      // Scope is an object, use its class
      scope = scope.$$class;
    }

    module = find_existing_module(scope, name);

    if (module == null) {
      // Module doesnt exist, create a new one...
      module = $allocate_module(name);
      $const_set(scope, name, module);
    }

    if (Opal.trace_class) { invoke_tracers_for_class(module); }

    return module;
  };

  // Return the singleton class for the passed object.
  //
  // If the given object alredy has a singleton class, then it will be stored on
  // the object as the `$$meta` property. If this exists, then it is simply
  // returned back.
  //
  // Otherwise, a new singleton object for the class or object is created, set on
  // the object at `$$meta` for future use, and then returned.
  //
  // @param object [Object] the ruby object
  // @return [Class] the singleton class for object
  Opal.get_singleton_class = function(object) {
    if (object.$$is_number) {
      $raise(Opal.TypeError, "can't define singleton");
    }
    if (object.$$meta) {
      return object.$$meta;
    }

    if (object.hasOwnProperty('$$is_class')) {
      return Opal.build_class_singleton_class(object);
    } else if (object.hasOwnProperty('$$is_module')) {
      return Opal.build_module_singleton_class(object);
    } else {
      return Opal.build_object_singleton_class(object);
    }
  };

  // helper to set $$meta on klass, module or instance
  function set_meta(obj, meta) {
    if (obj.hasOwnProperty('$$meta')) {
      obj.$$meta = meta;
    } else {
      $prop(obj, '$$meta', meta);
    }
    if (obj.$$frozen) {
      // If a object is frozen (sealed), freeze $$meta too.
      // No need to inject $$meta.$$prototype in the prototype chain,
      // as $$meta cannot be modified anyway.
      obj.$$meta.$freeze();
    } else {
      $set_proto(obj, meta.$$prototype);
    }
  };

  // Build the singleton class for an existing class. Class object are built
  // with their singleton class already in the prototype chain and inheriting
  // from their superclass object (up to `Class` itself).
  //
  // NOTE: Actually in MRI a class' singleton class inherits from its
  // superclass' singleton class which in turn inherits from Class.
  //
  // @param klass [Class]
  // @return [Class]
  Opal.build_class_singleton_class = function(klass) {
    if (klass.$$meta) {
      return klass.$$meta;
    }

    // The singleton_class superclass is the singleton_class of its superclass;
    // but BasicObject has no superclass (its `$$super` is null), thus we
    // fallback on `Class`.
    var superclass = klass === BasicObject ? Class : Opal.get_singleton_class(klass.$$super);

    var meta = $allocate_class(null, superclass, true);

    $prop(meta, '$$is_singleton', true);
    $prop(meta, '$$singleton_of', klass);
    set_meta(klass, meta);
    // Restoring ClassName.class
    $prop(klass, '$$class', Opal.Class);

    return meta;
  };

  Opal.build_module_singleton_class = function(mod) {
    if (mod.$$meta) {
      return mod.$$meta;
    }

    var meta = $allocate_class(null, Opal.Module, true);

    $prop(meta, '$$is_singleton', true);
    $prop(meta, '$$singleton_of', mod);
    set_meta(mod, meta);
    // Restoring ModuleName.class
    $prop(mod, '$$class', Opal.Module);

    return meta;
  };

  // Build the singleton class for a Ruby (non class) Object.
  //
  // @param object [Object]
  // @return [Class]
  Opal.build_object_singleton_class = function(object) {
    var superclass = object.$$class,
        klass = $allocate_class(nil, superclass, true);

    $prop(klass, '$$is_singleton', true);
    $prop(klass, '$$singleton_of', object);

    delete klass.$$prototype.$$class;

    set_meta(object, klass);

    return klass;
  };

  Opal.is_method = function(prop) {
    return (prop[0] === '$' && prop[1] !== '$');
  };

  Opal.instance_methods = function(mod) {
    var processed = Object.create(null), results = [], ancestors = $ancestors(mod);

    for (var i = 0, l = ancestors.length; i < l; i++) {
      var ancestor = ancestors[i],
          proto = ancestor.$$prototype;

      if (proto.hasOwnProperty('$$dummy')) {
        proto = proto.$$define_methods_on;
      }

      var props = Object.getOwnPropertyNames(proto);

      for (var j = 0, ll = props.length; j < ll; j++) {
        var prop = props[j];

        if (processed[prop]) {
          continue;
        }
        if (Opal.is_method(prop)) {
          var method = proto[prop];

          if (!method.$$stub) {
            var method_name = prop.slice(1);
            results.push(method_name);
          }
        }
        processed[prop] = true;
      }
    }

    return results;
  };

  Opal.own_instance_methods = function(mod) {
    var results = [],
        proto = mod.$$prototype;

    if (proto.hasOwnProperty('$$dummy')) {
      proto = proto.$$define_methods_on;
    }

    var props = Object.getOwnPropertyNames(proto);

    for (var i = 0, length = props.length; i < length; i++) {
      var prop = props[i];

      if (Opal.is_method(prop)) {
        var method = proto[prop];

        if (!method.$$stub) {
          var method_name = prop.slice(1);
          results.push(method_name);
        }
      }
    }

    return results;
  };

  Opal.methods = function(obj) {
    return Opal.instance_methods(obj.$$meta || obj.$$class);
  };

  Opal.own_methods = function(obj) {
    return obj.$$meta ? Opal.own_instance_methods(obj.$$meta) : [];
  };

  Opal.receiver_methods = function(obj) {
    var mod = Opal.get_singleton_class(obj);
    var singleton_methods = Opal.own_instance_methods(mod);
    var instance_methods = Opal.own_instance_methods(mod.$$super);
    return singleton_methods.concat(instance_methods);
  };

  // Returns an object containing all pairs of names/values
  // for all class variables defined in provided +module+
  // and its ancestors.
  //
  // @param module [Module]
  // @return [Object]
  Opal.class_variables = function(module) {
    var ancestors = $ancestors(module),
        i, length = ancestors.length,
        result = {};

    for (i = length - 1; i >= 0; i--) {
      var ancestor = ancestors[i];

      for (var cvar in ancestor.$$cvars) {
        result[cvar] = ancestor.$$cvars[cvar];
      }
    }

    return result;
  };

  // Sets class variable with specified +name+ to +value+
  // in provided +module+
  //
  // @param module [Module]
  // @param name [String]
  // @param value [Object]
  Opal.class_variable_set = function(module, name, value) {
    var ancestors = $ancestors(module),
        i, length = ancestors.length;

    for (i = length - 2; i >= 0; i--) {
      var ancestor = ancestors[i];

      if ($has_own(ancestor.$$cvars, name)) {
        ancestor.$$cvars[name] = value;
        return value;
      }
    }

    module.$$cvars[name] = value;

    return value;
  };

  // Gets class variable with specified +name+ from provided +module+
  //
  // @param module [Module]
  // @param name [String]
  Opal.class_variable_get = function(module, name, tolerant) {
    if ($has_own(module.$$cvars, name))
      return module.$$cvars[name];

    var ancestors = $ancestors(module),
      i, length = ancestors.length;

    for (i = 0; i < length; i++) {
      var ancestor = ancestors[i];

      if ($has_own(ancestor.$$cvars, name)) {
        return ancestor.$$cvars[name];
      }
    }

    if (!tolerant)
      $raise(Opal.NameError, 'uninitialized class variable '+name+' in '+module.$name());

    return nil;
  }

  function isRoot(proto) {
    return proto.hasOwnProperty('$$iclass') && proto.hasOwnProperty('$$root');
  }

  function own_included_modules(module) {
    var result = [], mod, proto = Object.getPrototypeOf(module.$$prototype);

    while (proto) {
      if (proto.hasOwnProperty('$$class')) {
        // superclass
        break;
      }
      mod = protoToModule(proto);
      if (mod) {
        result.push(mod);
      }
      proto = Object.getPrototypeOf(proto);
    }

    return result;
  }

  function own_prepended_modules(module) {
    var result = [], mod, proto = Object.getPrototypeOf(module.$$prototype);

    if (module.$$prototype.hasOwnProperty('$$dummy')) {
      while (proto) {
        if (proto === module.$$prototype.$$define_methods_on) {
          break;
        }

        mod = protoToModule(proto);
        if (mod) {
          result.push(mod);
        }

        proto = Object.getPrototypeOf(proto);
      }
    }

    return result;
  }


  // The actual inclusion of a module into a class.
  //
  // ## Class `$$parent` and `iclass`
  //
  // To handle `super` calls, every class has a `$$parent`. This parent is
  // used to resolve the next class for a super call. A normal class would
  // have this point to its superclass. However, if a class includes a module
  // then this would need to take into account the module. The module would
  // also have to then point its `$$parent` to the actual superclass. We
  // cannot modify modules like this, because it might be included in more
  // then one class. To fix this, we actually insert an `iclass` as the class'
  // `$$parent` which can then point to the superclass. The `iclass` acts as
  // a proxy to the actual module, so the `super` chain can then search it for
  // the required method.
  //
  // @param module [Module] the module to include
  // @param includer [Module] the target class to include module into
  // @return [null]
  Opal.append_features = function(module, includer) {
    var module_ancestors = $ancestors(module);
    var iclasses = [];

    if (module_ancestors.indexOf(includer) !== -1) {
      $raise(Opal.ArgumentError, 'cyclic include detected');
    }

    for (var i = 0, length = module_ancestors.length; i < length; i++) {
      var ancestor = module_ancestors[i], iclass = create_iclass(ancestor);
      $prop(iclass, '$$included', true);
      iclasses.push(iclass);
    }
    var includer_ancestors = $ancestors(includer),
        chain = chain_iclasses(iclasses),
        start_chain_after,
        end_chain_on;

    if (includer_ancestors.indexOf(module) === -1) {
      // first time include

      // includer -> chain.first -> ...chain... -> chain.last -> includer.parent
      start_chain_after = includer.$$prototype;
      end_chain_on = Object.getPrototypeOf(includer.$$prototype);
    } else {
      // The module has been already included,
      // we don't need to put it into the ancestors chain again,
      // but this module may have new included modules.
      // If it's true we need to copy them.
      //
      // The simplest way is to replace ancestors chain from
      //          parent
      //            |
      //   `module` iclass (has a $$root flag)
      //            |
      //   ...previos chain of module.included_modules ...
      //            |
      //  "next ancestor" (has a $$root flag or is a real class)
      //
      // to
      //          parent
      //            |
      //    `module` iclass (has a $$root flag)
      //            |
      //   ...regenerated chain of module.included_modules
      //            |
      //   "next ancestor" (has a $$root flag or is a real class)
      //
      // because there are no intermediate classes between `parent` and `next ancestor`.
      // It doesn't break any prototypes of other objects as we don't change class references.

      var parent = includer.$$prototype, module_iclass = Object.getPrototypeOf(parent);

      while (module_iclass != null) {
        if (module_iclass.$$module === module && isRoot(module_iclass)) {
          break;
        }

        parent = module_iclass;
        module_iclass = Object.getPrototypeOf(module_iclass);
      }

      if (module_iclass) {
        // module has been directly included
        var next_ancestor = Object.getPrototypeOf(module_iclass);

        // skip non-root iclasses (that were recursively included)
        while (next_ancestor.hasOwnProperty('$$iclass') && !isRoot(next_ancestor)) {
          next_ancestor = Object.getPrototypeOf(next_ancestor);
        }

        start_chain_after = parent;
        end_chain_on = next_ancestor;
      } else {
        // module has not been directly included but was in ancestor chain because it was included by another module
        // include it directly
        start_chain_after = includer.$$prototype;
        end_chain_on = Object.getPrototypeOf(includer.$$prototype);
      }
    }

    $set_proto(start_chain_after, chain.first);
    $set_proto(chain.last, end_chain_on);

    // recalculate own_included_modules cache
    includer.$$own_included_modules = own_included_modules(includer);

    Opal.const_cache_version++;
  };

  Opal.prepend_features = function(module, prepender) {
    // Here we change the ancestors chain from
    //
    //   prepender
    //      |
    //    parent
    //
    // to:
    //
    // dummy(prepender)
    //      |
    //  iclass(module)
    //      |
    // iclass(prepender)
    //      |
    //    parent
    var module_ancestors = $ancestors(module);
    var iclasses = [];

    if (module_ancestors.indexOf(prepender) !== -1) {
      $raise(Opal.ArgumentError, 'cyclic prepend detected');
    }

    for (var i = 0, length = module_ancestors.length; i < length; i++) {
      var ancestor = module_ancestors[i], iclass = create_iclass(ancestor);
      $prop(iclass, '$$prepended', true);
      iclasses.push(iclass);
    }

    var chain = chain_iclasses(iclasses),
        dummy_prepender = prepender.$$prototype,
        previous_parent = Object.getPrototypeOf(dummy_prepender),
        prepender_iclass,
        start_chain_after,
        end_chain_on;

    if (dummy_prepender.hasOwnProperty('$$dummy')) {
      // The module already has some prepended modules
      // which means that we don't need to make it "dummy"
      prepender_iclass = dummy_prepender.$$define_methods_on;
    } else {
      // Making the module "dummy"
      prepender_iclass = create_dummy_iclass(prepender);
      flush_methods_in(prepender);
      $prop(dummy_prepender, '$$dummy', true);
      $prop(dummy_prepender, '$$define_methods_on', prepender_iclass);

      // Converting
      //   dummy(prepender) -> previous_parent
      // to
      //   dummy(prepender) -> iclass(prepender) -> previous_parent
      $set_proto(dummy_prepender, prepender_iclass);
      $set_proto(prepender_iclass, previous_parent);
    }

    var prepender_ancestors = $ancestors(prepender);

    if (prepender_ancestors.indexOf(module) === -1) {
      // first time prepend

      start_chain_after = dummy_prepender;

      // next $$root or prepender_iclass or non-$$iclass
      end_chain_on = Object.getPrototypeOf(dummy_prepender);
      while (end_chain_on != null) {
        if (
          end_chain_on.hasOwnProperty('$$root') ||
          end_chain_on === prepender_iclass ||
          !end_chain_on.hasOwnProperty('$$iclass')
        ) {
          break;
        }

        end_chain_on = Object.getPrototypeOf(end_chain_on);
      }
    } else {
      $raise(Opal.RuntimeError, "Prepending a module multiple times is not supported");
    }

    $set_proto(start_chain_after, chain.first);
    $set_proto(chain.last, end_chain_on);

    // recalculate own_prepended_modules cache
    prepender.$$own_prepended_modules = own_prepended_modules(prepender);

    Opal.const_cache_version++;
  };

  function flush_methods_in(module) {
    var proto = module.$$prototype,
        props = Object.getOwnPropertyNames(proto);

    for (var i = 0; i < props.length; i++) {
      var prop = props[i];
      if (Opal.is_method(prop)) {
        delete proto[prop];
      }
    }
  }

  function create_iclass(module) {
    var iclass = create_dummy_iclass(module);

    if (module.$$is_module) {
      module.$$iclasses.push(iclass);
    }

    return iclass;
  }

  // Dummy iclass doesn't receive updates when the module gets a new method.
  function create_dummy_iclass(module) {
    var iclass = {},
        proto = module.$$prototype;

    if (proto.hasOwnProperty('$$dummy')) {
      proto = proto.$$define_methods_on;
    }

    var props = Object.getOwnPropertyNames(proto),
        length = props.length, i;

    for (i = 0; i < length; i++) {
      var prop = props[i];
      $prop(iclass, prop, proto[prop]);
    }

    $prop(iclass, '$$iclass', true);
    $prop(iclass, '$$module', module);

    return iclass;
  }

  function chain_iclasses(iclasses) {
    var length = iclasses.length, first = iclasses[0];

    $prop(first, '$$root', true);

    if (length === 1) {
      return { first: first, last: first };
    }

    var previous = first;

    for (var i = 1; i < length; i++) {
      var current = iclasses[i];
      $set_proto(previous, current);
      previous = current;
    }


    return { first: iclasses[0], last: iclasses[length - 1] };
  }

  // For performance, some core Ruby classes are toll-free bridged to their
  // native JavaScript counterparts (e.g. a Ruby Array is a JavaScript Array).
  //
  // This method is used to setup a native constructor (e.g. Array), to have
  // its prototype act like a normal Ruby class. Firstly, a new Ruby class is
  // created using the native constructor so that its prototype is set as the
  // target for the new class. Note: all bridged classes are set to inherit
  // from Object.
  //
  // Example:
  //
  //    Opal.bridge(self, Function);
  //
  // @param klass       [Class] the Ruby class to bridge
  // @param constructor [JS.Function] native JavaScript constructor to use
  // @return [Class] returns the passed Ruby class
  //
  Opal.bridge = function(native_klass, klass) {
    if (native_klass.hasOwnProperty('$$bridge')) {
      $raise(Opal.ArgumentError, "already bridged");
    }

    // constructor is a JS function with a prototype chain like:
    // - constructor
    //   - super
    //
    // What we need to do is to inject our class (with its prototype chain)
    // between constructor and super. For example, after injecting ::Object
    // into JS String we get:
    //
    // - constructor (window.String)
    //   - Opal.Object
    //     - Opal.Kernel
    //       - Opal.BasicObject
    //         - super (window.Object)
    //           - null
    //
    $prop(native_klass, '$$bridge', klass);
    $set_proto(native_klass.prototype, (klass.$$super || Opal.Object).$$prototype);
    $prop(klass, '$$prototype', native_klass.prototype);

    $prop(klass.$$prototype, '$$class', klass);
    $prop(klass, '$$constructor', native_klass);
    $prop(klass, '$$bridge', true);
  };

  function protoToModule(proto) {
    if (proto.hasOwnProperty('$$dummy')) {
      return;
    } else if (proto.hasOwnProperty('$$iclass')) {
      return proto.$$module;
    } else if (proto.hasOwnProperty('$$class')) {
      return proto.$$class;
    }
  }

  function own_ancestors(module) {
    return module.$$own_prepended_modules.concat([module]).concat(module.$$own_included_modules);
  }

  // The Array of ancestors for a given module/class
  function $ancestors(module) {
    if (!module) { return []; }

    if (module.$$ancestors_cache_version === Opal.const_cache_version) {
      return module.$$ancestors;
    }

    var result = [], i, mods, length;

    for (i = 0, mods = own_ancestors(module), length = mods.length; i < length; i++) {
      result.push(mods[i]);
    }

    if (module.$$super) {
      for (i = 0, mods = $ancestors(module.$$super), length = mods.length; i < length; i++) {
        result.push(mods[i]);
      }
    }

    module.$$ancestors_cache_version = Opal.const_cache_version;
    module.$$ancestors = result;

    return result;
  };
  Opal.ancestors = $ancestors;

  Opal.included_modules = function(module) {
    var result = [], mod = null, proto = Object.getPrototypeOf(module.$$prototype);

    for (; proto && Object.getPrototypeOf(proto); proto = Object.getPrototypeOf(proto)) {
      mod = protoToModule(proto);
      if (mod && mod.$$is_module && proto.$$iclass && proto.$$included) {
        result.push(mod);
      }
    }

    return result;
  };


  // Method Missing
  // --------------

  // Methods stubs are used to facilitate method_missing in opal. A stub is a
  // placeholder function which just calls `method_missing` on the receiver.
  // If no method with the given name is actually defined on an object, then it
  // is obvious to say that the stub will be called instead, and then in turn
  // method_missing will be called.
  //
  // When a file in ruby gets compiled to javascript, it includes a call to
  // this function which adds stubs for every method name in the compiled file.
  // It should then be safe to assume that method_missing will work for any
  // method call detected.
  //
  // Method stubs are added to the BasicObject prototype, which every other
  // ruby object inherits, so all objects should handle method missing. A stub
  // is only added if the given property name (method name) is not already
  // defined.
  //
  // Note: all ruby methods have a `$` prefix in javascript, so all stubs will
  // have this prefix as well (to make this method more performant).
  //
  //    Opal.add_stubs("foo,bar,baz=");
  //
  // All stub functions will have a private `$$stub` property set to true so
  // that other internal methods can detect if a method is just a stub or not.
  // `Kernel#respond_to?` uses this property to detect a methods presence.
  //
  // @param stubs [Array] an array of method stubs to add
  // @return [undefined]
  Opal.add_stubs = function(stubs) {
    var proto = Opal.BasicObject.$$prototype;
    var stub, existing_method;
    stubs = stubs.split(',');

    for (var i = 0, length = stubs.length; i < length; i++) {
      stub = $jsid(stubs[i]), existing_method = proto[stub];

      if (existing_method == null || existing_method.$$stub) {
        Opal.add_stub_for(proto, stub);
      }
    }
  };

  // Add a method_missing stub function to the given prototype for the
  // given name.
  //
  // @param prototype [Prototype] the target prototype
  // @param stub [String] stub name to add (e.g. "$foo")
  // @return [undefined]
  Opal.add_stub_for = function(prototype, stub) {
    // Opal.stub_for(stub) is the method_missing_stub
    $prop(prototype, stub, Opal.stub_for(stub));
  };

  // Generate the method_missing stub for a given method name.
  //
  // @param method_name [String] The js-name of the method to stub (e.g. "$foo")
  // @return [undefined]
  Opal.stub_for = function(method_name) {
    function method_missing_stub() {
      // Copy any given block onto the method_missing dispatcher
      this.$method_missing.$$p = method_missing_stub.$$p;

      // Set block property to null ready for the next call (stop false-positives)
      method_missing_stub.$$p = null;

      // call method missing with correct args (remove '$' prefix on method name)
      return this.$method_missing.apply(this, $prepend(method_name.slice(1), arguments));
    };

    method_missing_stub.$$stub = true;

    return method_missing_stub;
  };


  // Methods
  // -------

  // Arity count error dispatcher for methods
  //
  // @param actual [Fixnum] number of arguments given to method
  // @param expected [Fixnum] expected number of arguments
  // @param object [Object] owner of the method +meth+
  // @param meth [String] method name that got wrong number of arguments
  // @raise [ArgumentError]
  Opal.ac = function(actual, expected, object, meth) {
    var inspect = '';
    if (object.$$is_a_module) {
      inspect += object.$$name + '.';
    }
    else {
      inspect += object.$$class.$$name + '#';
    }
    inspect += meth;

    $raise(Opal.ArgumentError, '[' + inspect + '] wrong number of arguments (given ' + actual + ', expected ' + expected + ')');
  };

  // Arity count error dispatcher for blocks
  //
  // @param actual [Fixnum] number of arguments given to block
  // @param expected [Fixnum] expected number of arguments
  // @param context [Object] context of the block definition
  // @raise [ArgumentError]
  Opal.block_ac = function(actual, expected, context) {
    var inspect = "`block in " + context + "'";

    $raise(Opal.ArgumentError, inspect + ': wrong number of arguments (given ' + actual + ', expected ' + expected + ')');
  };

  function get_ancestors(obj) {
    if (obj.hasOwnProperty('$$meta') && obj.$$meta !== null) {
      return $ancestors(obj.$$meta);
    } else {
      return $ancestors(obj.$$class);
    }
  };

  // Super dispatcher
  Opal.find_super = function(obj, mid, current_func, defcheck, allow_stubs) {
    var jsid = $jsid(mid), ancestors, ancestor, super_method, method_owner, current_index = -1, i;

    ancestors = get_ancestors(obj);
    method_owner = current_func.$$owner;

    for (i = 0; i < ancestors.length; i++) {
      ancestor = ancestors[i];
      if (ancestor === method_owner || ancestor.$$cloned_from.indexOf(method_owner) !== -1) {
        current_index = i;
        break;
      }
    }

    for (i = current_index + 1; i < ancestors.length; i++) {
      ancestor = ancestors[i];
      var proto = ancestor.$$prototype;

      if (proto.hasOwnProperty('$$dummy')) {
        proto = proto.$$define_methods_on;
      }

      if (proto.hasOwnProperty(jsid)) {
        super_method = proto[jsid];
        break;
      }
    }

    if (!defcheck && super_method && super_method.$$stub && obj.$method_missing.$$pristine) {
      // method_missing hasn't been explicitly defined
      $raise(Opal.NoMethodError, 'super: no superclass method `'+mid+"' for "+obj, mid);
    }

    return (super_method.$$stub && !allow_stubs) ? null : super_method;
  };

  // Iter dispatcher for super in a block
  Opal.find_block_super = function(obj, jsid, current_func, defcheck, implicit) {
    var call_jsid = jsid;

    if (!current_func) {
      $raise(Opal.RuntimeError, "super called outside of method");
    }

    if (implicit && current_func.$$define_meth) {
      $raise(Opal.RuntimeError,
        "implicit argument passing of super from method defined by define_method() is not supported. " +
        "Specify all arguments explicitly"
      );
    }

    if (current_func.$$def) {
      call_jsid = current_func.$$jsid;
    }

    return Opal.find_super(obj, call_jsid, current_func, defcheck);
  };

  // @deprecated
  Opal.find_super_dispatcher = Opal.find_super;

  // @deprecated
  Opal.find_iter_super_dispatcher = Opal.find_block_super;

  function call_lambda(block, arg, ret) {
    try {
      block(arg);
    } catch (e) {
      if (e === ret) {
        return ret.$v;
      }
      throw e;
    }
  }

  // handles yield calls for 1 yielded arg
  Opal.yield1 = function(block, arg) {
    if (typeof(block) !== "function") {
      $raise(Opal.LocalJumpError, "no block given");
    }

    var has_mlhs = block.$$has_top_level_mlhs_arg,
        has_trailing_comma = block.$$has_trailing_comma_in_args,
        is_returning_lambda = block.$$is_lambda && block.$$ret;

    if (block.length > 1 || ((has_mlhs || has_trailing_comma) && block.length === 1)) {
      arg = Opal.to_ary(arg);
    }

    if ((block.length > 1 || (has_trailing_comma && block.length === 1)) && arg.$$is_array) {
      if (is_returning_lambda) {
        return call_lambda(block.apply.bind(block, null), arg, block.$$ret);
      }
      return block.apply(null, arg);
    }
    else {
      if (is_returning_lambda) {
        return call_lambda(block, arg, block.$$ret);
      }
      return block(arg);
    }
  };

  // handles yield for > 1 yielded arg
  Opal.yieldX = function(block, args) {
    if (typeof(block) !== "function") {
      $raise(Opal.LocalJumpError, "no block given");
    }

    if (block.length > 1 && args.length === 1) {
      if (args[0].$$is_array) {
        args = args[0];
      }
    }

    if (block.$$is_lambda && block.$$ret) {
      return call_lambda(block.apply.bind(block, null), args, block.$$ret);
    }
    return block.apply(null, args);
  };

  // Finds the corresponding exception match in candidates.  Each candidate can
  // be a value, or an array of values.  Returns null if not found.
  Opal.rescue = function(exception, candidates) {
    for (var i = 0; i < candidates.length; i++) {
      var candidate = candidates[i];

      if (candidate.$$is_array) {
        var result = Opal.rescue(exception, candidate);

        if (result) {
          return result;
        }
      }
      else if (candidate === Opal.JS.Error || candidate['$==='](exception)) {
        return candidate;
      }
    }

    return null;
  };

  Opal.is_a = function(object, klass) {
    if (klass != null && object.$$meta === klass || object.$$class === klass) {
      return true;
    }

    if (object.$$is_number && klass.$$is_number_class) {
      return (klass.$$is_integer_class) ? (object % 1) === 0 : true;
    }

    var ancestors = $ancestors(object.$$is_class ? Opal.get_singleton_class(object) : (object.$$meta || object.$$class));

    return ancestors.indexOf(klass) !== -1;
  };

  // Helpers for extracting kwsplats
  // Used for: { **h }
  Opal.to_hash = function(value) {
    if (value.$$is_hash) {
      return value;
    }
    else if (value['$respond_to?']('to_hash', true)) {
      var hash = value.$to_hash();
      if (hash.$$is_hash) {
        return hash;
      }
      else {
        $raise(Opal.TypeError, "Can't convert " + value.$$class +
          " to Hash (" + value.$$class + "#to_hash gives " + hash.$$class + ")");
      }
    }
    else {
      $raise(Opal.TypeError, "no implicit conversion of " + value.$$class + " into Hash");
    }
  };

  // Helpers for implementing multiple assignment
  // Our code for extracting the values and assigning them only works if the
  // return value is a JS array.
  // So if we get an Array subclass, extract the wrapped JS array from it

  // Used for: a, b = something (no splat)
  Opal.to_ary = function(value) {
    if (value.$$is_array) {
      return value;
    }
    else if (value['$respond_to?']('to_ary', true)) {
      var ary = value.$to_ary();
      if (ary === nil) {
        return [value];
      }
      else if (ary.$$is_array) {
        return ary;
      }
      else {
        $raise(Opal.TypeError, "Can't convert " + value.$$class +
          " to Array (" + value.$$class + "#to_ary gives " + ary.$$class + ")");
      }
    }
    else {
      return [value];
    }
  };

  // Used for: a, b = *something (with splat)
  Opal.to_a = function(value) {
    if (value.$$is_array) {
      // A splatted array must be copied
      return value.slice();
    }
    else if (value['$respond_to?']('to_a', true)) {
      var ary = value.$to_a();
      if (ary === nil) {
        return [value];
      }
      else if (ary.$$is_array) {
        return ary;
      }
      else {
        $raise(Opal.TypeError, "Can't convert " + value.$$class +
          " to Array (" + value.$$class + "#to_a gives " + ary.$$class + ")");
      }
    }
    else {
      return [value];
    }
  };

  // Used for extracting keyword arguments from arguments passed to
  // JS function.
  //
  // @param parameters [Array]
  // @return [Hash] or undefined
  //
  Opal.extract_kwargs = function(parameters) {
    var kwargs = parameters[parameters.length - 1];
    if (kwargs != null && Opal.respond_to(kwargs, '$to_hash', true)) {
      $splice(parameters, parameters.length - 1);
      return kwargs;
    }
  };

  // Used to get a list of rest keyword arguments. Method takes the given
  // keyword args, i.e. the hash literal passed to the method containing all
  // keyword arguments passed to method, as well as the used args which are
  // the names of required and optional arguments defined. This method then
  // just returns all key/value pairs which have not been used, in a new
  // hash literal.
  //
  // @param given_args [Hash] all kwargs given to method
  // @param used_args [Object<String: true>] all keys used as named kwargs
  // @return [Hash]
  //
  Opal.kwrestargs = function(given_args, used_args) {
    var map = new Map();

    Opal.hash_each(given_args, false, function(key, value) {
      if (!used_args[key]) {
        Opal.hash_put(map, key, value);
      }
      return [false, false];
    });

    return map;
  };

  function apply_blockopts(block, blockopts) {
    if (typeof(blockopts) === 'number') {
      block.$$arity = blockopts;
    }
    else if (typeof(blockopts) === 'object') {
      Object.assign(block, blockopts);
    }
  }

  // Optimization for a costly operation of prepending '$' to method names
  var jsid_cache = new Map();
  function $jsid(name) {
    var jsid = jsid_cache.get(name);
    if (!jsid) {
      jsid = '$' + name;
      jsid_cache.set(name, jsid);
    }
    return jsid;
  }
  Opal.jsid = $jsid;

  function $prepend(first, second) {
    if (!second.$$is_array) second = $slice(second);
    return [first].concat(second);
  }

  // Calls passed method on a ruby object with arguments and block:
  //
  // Can take a method or a method name.
  //
  // 1. When method name gets passed it invokes it by its name
  //    and calls 'method_missing' when object doesn't have this method.
  //    Used internally by Opal to invoke method that takes a block or a splat.
  // 2. When method (i.e. method body) gets passed, it doesn't trigger 'method_missing'
  //    because it doesn't know the name of the actual method.
  //    Used internally by Opal to invoke 'super'.
  //
  // @example
  //   var my_array = [1, 2, 3, 4]
  //   Opal.send(my_array, 'length')                    # => 4
  //   Opal.send(my_array, my_array.$length)            # => 4
  //
  //   Opal.send(my_array, 'reverse!')                  # => [4, 3, 2, 1]
  //   Opal.send(my_array, my_array['$reverse!']')      # => [4, 3, 2, 1]
  //
  // @param recv [Object] ruby object
  // @param method [Function, String] method body or name of the method
  // @param args [Array] arguments that will be passed to the method call
  // @param block [Function] ruby block
  // @param blockopts [Object, Number] optional properties to set on the block
  // @return [Object] returning value of the method call
  Opal.send = function(recv, method, args, block, blockopts) {
    var body;

    if (typeof(method) === 'function') {
      body = method;
      method = null;
    } else if (typeof(method) === 'string') {
      body = recv[$jsid(method)];
    } else {
      $raise(Opal.NameError, "Passed method should be a string or a function");
    }

    return Opal.send2(recv, body, method, args, block, blockopts);
  };

  Opal.send2 = function(recv, body, method, args, block, blockopts) {
    if (body == null && method != null && recv.$method_missing) {
      body = recv.$method_missing;
      args = $prepend(method, args);
    }

    apply_blockopts(block, blockopts);

    if (typeof block === 'function') body.$$p = block;
    return body.apply(recv, args);
  };

  Opal.refined_send = function(refinement_groups, recv, method, args, block, blockopts) {
    var i, j, k, ancestors, ancestor, refinements, refinement, refine_modules, refine_module, body;

    ancestors = get_ancestors(recv);

    // For all ancestors that there are, starting from the closest to the furthest...
    for (i = 0; i < ancestors.length; i++) {
      ancestor = Opal.id(ancestors[i]);

      // For all refinement groups there are, starting from the closest scope to the furthest...
      for (j = 0; j < refinement_groups.length; j++) {
        refinements = refinement_groups[j];

        // For all refinements there are, starting from the last `using` call to the furthest...
        for (k = refinements.length - 1; k >= 0; k--) {
          refinement = refinements[k];
          if (typeof refinement.$$refine_modules === 'undefined') continue;

          // A single module being given as an argument of the `using` call contains multiple
          // refinement modules
          refine_modules = refinement.$$refine_modules;

          // Does this module refine a given call for a given ancestor module?
          if (typeof refine_modules[ancestor] === 'undefined') continue;
          refine_module = refine_modules[ancestor];

          // Does this module define a method we want to call?
          if (typeof refine_module.$$prototype[$jsid(method)] !== 'undefined') {
            body = refine_module.$$prototype[$jsid(method)];
            return Opal.send2(recv, body, method, args, block, blockopts);
          }
        }
      }
    }

    return Opal.send(recv, method, args, block, blockopts);
  };

  Opal.lambda = function(block, blockopts) {
    block.$$is_lambda = true;

    apply_blockopts(block, blockopts);

    return block;
  };

  // Used to define methods on an object. This is a helper method, used by the
  // compiled source to define methods on special case objects when the compiler
  // can not determine the destination object, or the object is a Module
  // instance. This can get called by `Module#define_method` as well.
  //
  // ## Modules
  //
  // Any method defined on a module will come through this runtime helper.
  // The method is added to the module body, and the owner of the method is
  // set to be the module itself. This is used later when choosing which
  // method should show on a class if more than 1 included modules define
  // the same method. Finally, if the module is in `module_function` mode,
  // then the method is also defined onto the module itself.
  //
  // ## Classes
  //
  // This helper will only be called for classes when a method is being
  // defined indirectly; either through `Module#define_method`, or by a
  // literal `def` method inside an `instance_eval` or `class_eval` body. In
  // either case, the method is simply added to the class' prototype. A special
  // exception exists for `BasicObject` and `Object`. These two classes are
  // special because they are used in toll-free bridged classes. In each of
  // these two cases, extra work is required to define the methods on toll-free
  // bridged class' prototypes as well.
  //
  // ## Objects
  //
  // If a simple ruby object is the object, then the method is simply just
  // defined on the object as a singleton method. This would be the case when
  // a method is defined inside an `instance_eval` block.
  //
  // @param obj  [Object, Class] the actual obj to define method for
  // @param jsid [String] the JavaScript friendly method name (e.g. '$foo')
  // @param body [JS.Function] the literal JavaScript function used as method
  // @param blockopts [Object, Number] optional properties to set on the body
  // @return [null]
  //
  Opal.def = function(obj, jsid, body, blockopts) {
    apply_blockopts(body, blockopts);

    // Special case for a method definition in the
    // top-level namespace
    if (obj === Opal.top) {
      return Opal.defn(Opal.Object, jsid, body);
    }
    // if instance_eval is invoked on a module/class, it sets inst_eval_mod
    else if (!obj.$$eval && obj.$$is_a_module) {
      return Opal.defn(obj, jsid, body);
    }
    else {
      return Opal.defs(obj, jsid, body);
    }
  };

  // Define method on a module or class (see Opal.def).
  Opal.defn = function(module, jsid, body) {
    $deny_frozen_access(module);

    body.displayName = jsid;
    body.$$owner = module;

    var name = jsid.substr(1);

    var proto = module.$$prototype;
    if (proto.hasOwnProperty('$$dummy')) {
      proto = proto.$$define_methods_on;
    }
    $prop(proto, jsid, body);

    if (module.$$is_module) {
      if (module.$$module_function) {
        Opal.defs(module, jsid, body)
      }

      for (var i = 0, iclasses = module.$$iclasses, length = iclasses.length; i < length; i++) {
        var iclass = iclasses[i];
        $prop(iclass, jsid, body);
      }
    }

    var singleton_of = module.$$singleton_of;
    if (module.$method_added && !module.$method_added.$$stub && !singleton_of) {
      module.$method_added(name);
    }
    else if (singleton_of && singleton_of.$singleton_method_added && !singleton_of.$singleton_method_added.$$stub) {
      singleton_of.$singleton_method_added(name);
    }

    return name;
  };

  // Define a singleton method on the given object (see Opal.def).
  Opal.defs = function(obj, jsid, body, blockopts) {
    apply_blockopts(body, blockopts);

    if (obj.$$is_string || obj.$$is_number) {
      $raise(Opal.TypeError, "can't define singleton");
    }
    return Opal.defn(Opal.get_singleton_class(obj), jsid, body);
  };

  // Since JavaScript has no concept of modules, we create proxy classes
  // called `iclasses` that store copies of methods loaded. We need to
  // update them if we remove a method.
  function remove_method_from_iclasses(obj, jsid) {
    if (obj.$$is_module) {
      for (var i = 0, iclasses = obj.$$iclasses, length = iclasses.length; i < length; i++) {
        var iclass = iclasses[i];
        delete iclass[jsid];
      }
    }
  }

  // Called from #remove_method.
  Opal.rdef = function(obj, jsid) {
    if (!$has_own(obj.$$prototype, jsid)) {
      $raise(Opal.NameError, "method '" + jsid.substr(1) + "' not defined in " + obj.$name());
    }

    delete obj.$$prototype[jsid];

    remove_method_from_iclasses(obj, jsid);

    if (obj.$$is_singleton) {
      if (obj.$$prototype.$singleton_method_removed && !obj.$$prototype.$singleton_method_removed.$$stub) {
        obj.$$prototype.$singleton_method_removed(jsid.substr(1));
      }
    }
    else {
      if (obj.$method_removed && !obj.$method_removed.$$stub) {
        obj.$method_removed(jsid.substr(1));
      }
    }
  };

  // Called from #undef_method.
  Opal.udef = function(obj, jsid) {
    if (!obj.$$prototype[jsid] || obj.$$prototype[jsid].$$stub) {
      $raise(Opal.NameError, "method '" + jsid.substr(1) + "' not defined in " + obj.$name());
    }

    Opal.add_stub_for(obj.$$prototype, jsid);

    remove_method_from_iclasses(obj, jsid);

    if (obj.$$is_singleton) {
      if (obj.$$prototype.$singleton_method_undefined && !obj.$$prototype.$singleton_method_undefined.$$stub) {
        obj.$$prototype.$singleton_method_undefined(jsid.substr(1));
      }
    }
    else {
      if (obj.$method_undefined && !obj.$method_undefined.$$stub) {
        obj.$method_undefined(jsid.substr(1));
      }
    }
  };

  function is_method_body(body) {
    return (typeof(body) === "function" && !body.$$stub);
  }

  Opal.alias = function(obj, name, old) {
    var id     = $jsid(name),
        old_id = $jsid(old),
        body,
        alias;

    // Aliasing on main means aliasing on Object...
    if (typeof obj.$$prototype === 'undefined') {
      obj = Opal.Object;
    }

    body = obj.$$prototype[old_id];

    // When running inside #instance_eval the alias refers to class methods.
    if (obj.$$eval) {
      return Opal.alias(Opal.get_singleton_class(obj), name, old);
    }

    if (!is_method_body(body)) {
      var ancestor = obj.$$super;

      while (typeof(body) !== "function" && ancestor) {
        body     = ancestor[old_id];
        ancestor = ancestor.$$super;
      }

      if (!is_method_body(body) && obj.$$is_module) {
        // try to look into Object
        body = Opal.Object.$$prototype[old_id]
      }

      if (!is_method_body(body)) {
        $raise(Opal.NameError, "undefined method `" + old + "' for class `" + obj.$name() + "'")
      }
    }

    // If the body is itself an alias use the original body
    // to keep the max depth at 1.
    if (body.$$alias_of) body = body.$$alias_of;

    // We need a wrapper because otherwise properties
    // would be overwritten on the original body.
    alias = Opal.wrap_method_body(body);

    // Try to make the browser pick the right name
    alias.displayName  = name;
    alias.$$alias_of   = body;
    alias.$$alias_name = name;

    Opal.defn(obj, id, alias);

    return obj;
  };

  Opal.wrap_method_body = function(body) {
    var wrapped = function() {
      var block = wrapped.$$p;

      wrapped.$$p = null;

      return Opal.send(this, body, arguments, block);
    };

    // Assign the 'length' value with defineProperty because
    // in strict mode the property is not writable.
    // It doesn't work in older browsers (like Chrome 38), where
    // an exception is thrown breaking Opal altogether.
    try {
      Object.defineProperty(wrapped, 'length', { value: body.length });
    } catch (e) {}

    wrapped.$$arity           = body.$$arity == null ? body.length : body.$$arity;
    wrapped.$$parameters      = body.$$parameters;
    wrapped.$$source_location = body.$$source_location;

    return wrapped;
  };

  Opal.alias_gvar = function(new_name, old_name) {
    Object.defineProperty($gvars, new_name, {
      configurable: true,
      enumerable: true,
      get: function() {
        return $gvars[old_name];
      },
      set: function(new_value) {
        $gvars[old_name] = new_value;
      }
    });
    return nil;
  }

  Opal.alias_native = function(obj, name, native_name) {
    var id   = $jsid(name),
        body = obj.$$prototype[native_name];

    if (typeof(body) !== "function" || body.$$stub) {
      $raise(Opal.NameError, "undefined native method `" + native_name + "' for class `" + obj.$name() + "'")
    }

    Opal.defn(obj, id, body);

    return obj;
  };


  // Hashes
  // ------

  Opal.hash_init = function (_hash) {
    console.warn("DEPRECATION: Opal.hash_init is deprecated and is now a no-op.");
  }

  Opal.hash_clone = function(from_hash, to_hash) {
    to_hash.$$none = from_hash.$$none;
    to_hash.$$proc = from_hash.$$proc;

    return Opal.hash_each(from_hash, to_hash, function(key, value) {
      Opal.hash_put(to_hash, key, value);
      return [false, to_hash];
    });
  };

  Opal.hash_put = function(hash, key, value) {
    var type = typeof key;
    if (type === "string" || type === "symbol" || type === "number" || type === "boolean" || type === "bigint") {
      hash.set(key, value)
    } else if (key.$$is_string) {
      hash.set(key.valueOf(), value);
    } else {
      if (!hash.$$keys)
        hash.$$keys = new Map();

      var key_hash = key.$$is_string ? key.valueOf() : (hash.$$by_identity ? Opal.id(key) : key.$hash()),
          keys = hash.$$keys;

      if (!keys.has(key_hash)) {
        keys.set(key_hash, [key]);
        hash.set(key, value);
        return;
      }

      var objects = keys.get(key_hash),
          object;

      for (var i=0; i<objects.length; i++) {
        object = objects[i];
        if (key === object || key['$eql?'](object)) {
          hash.set(object, value);
          return;
        }
      }

      objects.push(key);
      hash.set(key, value);
    }
  };

  Opal.hash_get = function(hash, key) {
    var type = typeof key;
    if (type === "string" || type === "symbol" || type === "number" || type === "boolean" || type === "bigint") {
      return hash.get(key)
    } else if (hash.$$keys) {
      var key_hash = key.$$is_string ? key.valueOf() : (hash.$$by_identity ? Opal.id(key) : key.$hash()),
          objects = hash.$$keys.get(key_hash),
          object;

      if (objects !== undefined) {
        for (var i=0; i<objects.length; i++) {
          object = objects[i];
          if (key === object || key['$eql?'](object))
            return hash.get(object);
        }
      } else if (key.$$is_string) {
        return hash.get(key_hash);
      }
    } else if (key.$$is_string) {
      return hash.get(key.valueOf());
    }
  };

  function $hash_delete_stage2(hash, key) {
    var value = hash.get(key);
    if (value !== undefined) {
      hash.delete(key);
      return value;
    }
  }

  Opal.hash_delete = function(hash, key) {
    var type = typeof key
    if (type === "string" || type === "symbol" || type === "number" || type === "boolean" || type === "bigint") {
      return $hash_delete_stage2(hash, key);
    } else if (hash.$$keys) {
      var key_hash = key.$$is_string ? key.valueOf() : (hash.$$by_identity ? Opal.id(key) : key.$hash()),
          objects = hash.$$keys.get(key_hash),
          object;

      if (objects !== undefined) {
        for (var i=0; i<objects.length; i++) {
          object = objects[i];
          if (key === object || key['$eql?'](object)) {
            objects.splice(i, 1);
            if (objects.length === 0)
              hash.$$keys.delete(key_hash);
            return $hash_delete_stage2(hash, object);
          }
        }
      } else if (key.$$is_string) {
        return $hash_delete_stage2(hash, key_hash);
      }
    } else if (key.$$is_string) {
      return $hash_delete_stage2(hash, key.valueOf());
    }
  };

  Opal.hash_rehash = function(hash) {
    var keys = hash.$$keys;

    if (keys)
      keys.clear();

    Opal.hash_each(hash, false, function(key, value) {
      var type = typeof key;
      if (type === "string" || type === "symbol" || type === "number" || type === "boolean" || type === "bigint")
        return [false, false]; // nothing to rehash

      var key_hash = key.$$is_string ? key.valueOf() : (hash.$$by_identity ? Opal.id(key) : key.$hash());

      if (!keys)
        hash.$$keys = keys = new Map();

      if (!keys.has(key_hash)) {
        keys.set(key_hash, [key]);
        return [false, false];
      }

      var objects = keys.get(key_hash),
          objects_copy = $slice(objects),
          object;

      for (var i=0; i<objects_copy.length; i++) {
        object = objects_copy[i];
        if (key === object || key['$eql?'](object)) {
          // got a duplicate, remove it
          objects.splice(objects.indexOf(object), 1);
          hash.delete(object);
        }
      }

      objects.push(key);

      return [false, false]
    });

    return hash;
  };

  Opal.hash = function () {
    var arguments_length = arguments.length,
      args,
      hash,
      i,
      length,
      key,
      value;

    if (arguments_length === 1 && arguments[0].$$is_hash) {
      return arguments[0];
    }

    hash = new Map();

    if (arguments_length === 1) {
      args = arguments[0];

      if (arguments[0].$$is_array) {
        length = args.length;

        for (i = 0; i < length; i++) {
          if (args[i].length !== 2) {
            $raise(Opal.ArgumentError, 'value not of length 2: ' + args[i].$inspect());
          }

          key = args[i][0];
          value = args[i][1];

          Opal.hash_put(hash, key, value);
        }

        return hash;
      } else {
        args = arguments[0];
        for (key in args) {
          if ($has_own(args, key)) {
            value = args[key];

            Opal.hash_put(hash, key, value);
          }
        }

        return hash;
      }
    }

    if (arguments_length % 2 !== 0) {
      $raise(Opal.ArgumentError, 'odd number of arguments for Hash');
    }

    for (i = 0; i < arguments_length; i += 2) {
      key = arguments[i];
      value = arguments[i + 1];

      Opal.hash_put(hash, key, value);
    }

    return hash;
  };

  // A faster Hash creator for hashes that just use symbols and
  // strings as keys. The map and keys array can be constructed at
  // compile time, so they are just added here by the constructor
  // function.
  //
  Opal.hash2 = function(keys, smap) {
    console.warn("DEPRECATION: `Opal.hash2` is deprecated and will be removed in Opal 2.0. Use `new Map()` with an array of key/value pairs instead.");

    var hash = new Map();
    for (var i = 0, max = keys.length; i < max; i++) {
      hash.set(keys[i], smap[keys[i]]);
    }
    return hash;
  };

  Opal.hash_each = function (hash, dres, fun) {
    // dres = default result, returned if hash is empty
    // fun is called as fun(key, value) and must return a array with [break, result]
    // if break is true, iteration stops and result is returned
    // if break is false, iteration continues and eventually the last result is returned
    var res;
    for (var i = 0, entry, entries = Array.from(hash.entries()), l = entries.length; i < l; i++) {
      entry = entries[i];
      res = fun(entry[0], entry[1]);
      if (res[0]) return res[1];
    }
    return res ? res[1] : dres;
  };

  // Create a new range instance with first and last values, and whether the
  // range excludes the last value.
  //
  Opal.range = function(first, last, exc) {
    var range         = new Opal.Range();
        range.begin   = first;
        range.end     = last;
        range.excl    = exc;

    return range;
  };

  var reserved_ivar_names = [
    // properties
    "constructor", "displayName", "__count__", "__noSuchMethod__",
    "__parent__", "__proto__",
    // methods
    "hasOwnProperty", "valueOf"
  ];

  // Get the ivar name for a given name.
  // Mostly adds a trailing $ to reserved names.
  //
  Opal.ivar = function(name) {
    if (reserved_ivar_names.indexOf(name) !== -1) {
      name += "$";
    }

    return name;
  };

  // Support for #freeze
  // -------------------

  // helper that can be used from methods
  function $deny_frozen_access(obj) {
    if (obj.$$frozen) {
      $raise(Opal.FrozenError, "can't modify frozen " + (obj.$class()) + ": " + (obj), new Map([["receiver", obj]]));
    }
  };
  Opal.deny_frozen_access = $deny_frozen_access;

  // common #freeze runtime support
  Opal.freeze = function(obj) {
    $prop(obj, "$$frozen", true);

    // set $$id
    if (!obj.hasOwnProperty('$$id')) { $prop(obj, '$$id', $uid()); }

    if (obj.hasOwnProperty('$$meta')) {
      // freeze $$meta if it has already been set
      obj.$$meta.$freeze();
    } else {
      // ensure $$meta can be set lazily, $$meta is frozen when set in runtime.js
      $prop(obj, '$$meta', null);
    }

    // $$comparable is used internally and set multiple times
    // defining it before sealing ensures it can be modified later on
    if (!obj.hasOwnProperty('$$comparable')) { $prop(obj, '$$comparable', null); }

    // seal the Object
    Object.seal(obj);

    return obj;
  };

  // Iterate over every instance variable and call func for each one
  // giving name of the ivar and optionally the property descriptor.
  function $each_ivar(obj, func) {
    var own_props = Object.getOwnPropertyNames(obj), own_props_length = own_props.length, i, prop, desc;

    for(i = 0; i < own_props_length; i++) {
      prop = own_props[i];

      if (prop[0] === '$') continue;

      desc = Object.getOwnPropertyDescriptor(obj, prop);

      if (desc && desc.enumerable) {
        func(prop, desc);
      }
    }
  }

  Opal.each_ivar = $each_ivar;

  // freze props, make setters of instance variables throw FrozenError
  Opal.freeze_props = function(obj) {
    var dp_template = {
      get: null,
      set: function(_val) { $deny_frozen_access(obj); },
      enumerable: true
    };

    $each_ivar(obj, function(prop, desc) {
      if (!desc.writable) return;

      // Redefine a property with a setter that raises an error.
      dp_template.get = $return_val(desc.value);

      Object.defineProperty(obj, prop, dp_template);
    });
  };

  // Regexps
  // -------

  // Escape Regexp special chars letting the resulting string be used to build
  // a new Regexp.
  //
  Opal.escape_regexp = function(str) {
    return str.replace(/([-[\]\/{}()*+?.^$\\| ])/g, '\\$1')
              .replace(/[\n]/g, '\\n')
              .replace(/[\r]/g, '\\r')
              .replace(/[\f]/g, '\\f')
              .replace(/[\t]/g, '\\t');
  };

  // Create a global Regexp from a RegExp object and cache the result
  // on the object itself ($$g attribute).
  //
  Opal.global_regexp = function(pattern) {
    if (pattern.global) {
      return pattern; // RegExp already has the global flag
    }
    if (pattern.$$g == null) {
      pattern.$$g = new RegExp(pattern.source, (pattern.multiline ? 'gm' : 'g') + (pattern.ignoreCase ? 'i' : ''));
    } else {
      pattern.$$g.lastIndex = null; // reset lastIndex property
    }
    return pattern.$$g;
  };

  // Create a global multiline Regexp from a RegExp object and cache the result
  // on the object itself ($$gm or $$g attribute).
  //
  Opal.global_multiline_regexp = function(pattern) {
    var result, flags;

    // RegExp already has the global and multiline flag
    if (pattern.global && pattern.multiline) return pattern;

    flags = 'gm' + (pattern.ignoreCase ? 'i' : '');
    if (pattern.multiline) {
      // we are using the $$g attribute because the Regexp is already multiline
      if (pattern.$$g == null) {
        pattern.$$g = new RegExp(pattern.source, flags);
      }
      result = pattern.$$g;
    } else {
      if (pattern.$$gm == null) {
        pattern.$$gm = new RegExp(pattern.source, flags);
      }
      result = pattern.$$gm;
    }
    result.lastIndex = null; // reset lastIndex property
    return result;
  };

  // Combine multiple regexp parts together
  Opal.regexp = function(parts, flags) {
    var part;
    var ignoreCase = typeof flags !== 'undefined' && flags && flags.indexOf('i') >= 0;

    for (var i = 0, ii = parts.length; i < ii; i++) {
      part = parts[i];
      if (part instanceof RegExp) {
        if (part.ignoreCase !== ignoreCase)
          Opal.Kernel.$warn(
            "ignore case doesn't match for " + part.source.$inspect(),
            new Map([['uplevel',  1]])
          )

        part = part.source;
      }
      if (part === '') part = '(?:' + part + ')';
      parts[i] = part;
    }

    if (flags) {
      return new RegExp(parts.join(''), flags);
    } else {
      return new RegExp(parts.join(''));
    }
  };

  // Require system
  // --------------

  Opal.modules         = {};
  Opal.loaded_features = ['corelib/runtime'];
  Opal.current_dir     = '.';
  Opal.require_table   = {'corelib/runtime': true};

  Opal.normalize = function(path) {
    var parts, part, new_parts = [], SEPARATOR = '/';

    if (Opal.current_dir !== '.') {
      path = Opal.current_dir.replace(/\/*$/, '/') + path;
    }

    path = path.replace(/^\.\//, '');
    path = path.replace(/\.(rb|opal|js)$/, '');
    parts = path.split(SEPARATOR);

    for (var i = 0, ii = parts.length; i < ii; i++) {
      part = parts[i];
      if (part === '') continue;
      (part === '..') ? new_parts.pop() : new_parts.push(part)
    }

    return new_parts.join(SEPARATOR);
  };

  Opal.loaded = function(paths) {
    var i, l, path;

    for (i = 0, l = paths.length; i < l; i++) {
      path = Opal.normalize(paths[i]);

      if (Opal.require_table[path]) {
        continue;
      }

      Opal.loaded_features.push(path);
      Opal.require_table[path] = true;
    }
  };

  Opal.load_normalized = function(path) {
    Opal.loaded([path]);

    var module = Opal.modules[path];

    if (module) {
      var retval = module(Opal);
      if (typeof Promise !== 'undefined' && retval instanceof Promise) {
        // A special case of require having an async top:
        // We will need to await it.
        return retval.then($return_val(true));
      }
    }
    else {
      var severity = Opal.config.missing_require_severity;
      var message  = 'cannot load such file -- ' + path;

      if (severity === "error") {
        $raise(Opal.LoadError, message);
      }
      else if (severity === "warning") {
        console.warn('WARNING: LoadError: ' + message);
      }
    }

    return true;
  };

  Opal.load = function(path) {
    path = Opal.normalize(path);

    return Opal.load_normalized(path);
  };

  Opal.require = function(path) {
    path = Opal.normalize(path);

    if (Opal.require_table[path]) {
      return false;
    }

    return Opal.load_normalized(path);
  };


  // Strings
  // -------

  Opal.encodings = Object.create(null);

  // Sets the encoding on a string, will treat string literals as frozen strings
  // raising a FrozenError.
  //
  // @param str [String] the string on which the encoding should be set
  // @param name [String] the canonical name of the encoding
  // @param type [String] possible values are either `"encoding"`, `"internal_encoding"`, or `undefined
  Opal.set_encoding = function(str, name, type) {
    if (typeof type === "undefined") type = "encoding";
    if (typeof str === 'string' || str.$$frozen === true)
      $raise(Opal.FrozenError, "can't modify frozen String");

    var encoding = Opal.find_encoding(name);

    if (encoding === str[type]) { return str; }

    str[type] = encoding;

    return str;
  };

  // Fetches the encoding for the given name or raises ArgumentError.
  Opal.find_encoding = function(name) {
    var register = Opal.encodings;
    var encoding = register[name] || register[name.toUpperCase()];
    if (!encoding) $raise(Opal.ArgumentError, "unknown encoding name - " + name);
    return encoding;
  }

  // @returns a String object with the encoding set from a string literal
  Opal.enc = function(str, name) {
    var dup = new String(str);
    dup = Opal.set_encoding(dup, name);
    dup.internal_encoding = dup.encoding;
    return dup
  }

  // @returns a String object with the internal encoding set to Binary
  Opal.binary = function(str) {
    var dup = new String(str);
    return Opal.set_encoding(dup, "binary", "internal_encoding");
  }

  Opal.last_promise = null;
  Opal.promise_unhandled_exception = false;

  // Run a block of code, but if it returns a Promise, don't run the next
  // one, but queue it.
  Opal.queue = function(proc) {
    if (Opal.last_promise) {
      // The async path is taken only if anything before returned a
      // Promise(V2).
      Opal.last_promise = Opal.last_promise.then(function() {
        if (!Opal.promise_unhandled_exception) return proc(Opal);
      })['catch'](function(error) {
        if (Opal.respond_to(error, '$full_message')) {
          error = error.$full_message();
        }
        console.error(error);
        // Abort further execution
        Opal.promise_unhandled_exception = true;
        Opal.exit(1);
      });
      return Opal.last_promise;
    }
    else {
      var ret = proc(Opal);
      if (typeof Promise === 'function' && typeof ret === 'object' && ret instanceof Promise) {
        Opal.last_promise = ret;
      }
      return ret;
    }
  }

  // Operator helpers
  // ----------------

  function are_both_numbers(l,r) { return typeof(l) === 'number' && typeof(r) === 'number' }

  Opal.rb_plus   = function(l,r) { return are_both_numbers(l,r) ? l + r : l['$+'](r); }
  Opal.rb_minus  = function(l,r) { return are_both_numbers(l,r) ? l - r : l['$-'](r); }
  Opal.rb_times  = function(l,r) { return are_both_numbers(l,r) ? l * r : l['$*'](r); }
  Opal.rb_divide = function(l,r) { return are_both_numbers(l,r) ? l / r : l['$/'](r); }
  Opal.rb_lt     = function(l,r) { return are_both_numbers(l,r) ? l < r : l['$<'](r); }
  Opal.rb_gt     = function(l,r) { return are_both_numbers(l,r) ? l > r : l['$>'](r); }
  Opal.rb_le     = function(l,r) { return are_both_numbers(l,r) ? l <= r : l['$<='](r); }
  Opal.rb_ge     = function(l,r) { return are_both_numbers(l,r) ? l >= r : l['$>='](r); }

  // Optimized helpers for calls like $truthy((a)['$==='](b)) -> $eqeqeq(a, b)
  function are_both_numbers_or_strings(lhs, rhs) {
    return (typeof lhs === 'number' && typeof rhs === 'number') ||
           (typeof lhs === 'string' && typeof rhs === 'string');
  }

  function $eqeq(lhs, rhs) {
    return are_both_numbers_or_strings(lhs,rhs) ? lhs === rhs : $truthy((lhs)['$=='](rhs));
  };
  Opal.eqeq = $eqeq;
  Opal.eqeqeq = function(lhs, rhs) {
    return are_both_numbers_or_strings(lhs,rhs) ? lhs === rhs : $truthy((lhs)['$==='](rhs));
  };
  Opal.neqeq = function(lhs, rhs) {
    return are_both_numbers_or_strings(lhs,rhs) ? lhs !== rhs : $truthy((lhs)['$!='](rhs));
  };
  Opal.not = function(arg) {
    if (undefined === arg || null === arg || false === arg || nil === arg) return true;
    if (true === arg || arg['$!'].$$pristine) return false;
    return $truthy(arg['$!']());
  }

  // Shortcuts - optimized function generators for simple kinds of functions
  function $return_val(arg) {
    return function() {
      return arg;
    }
  }
  Opal.return_val = $return_val;

  Opal.return_self = function() {
    return this;
  }
  Opal.return_ivar = function(ivar) {
    return function() {
      if (this[ivar] == null) { return nil; }
      return this[ivar];
    }
  }
  Opal.assign_ivar = function(ivar) {
    return function(val) {
      $deny_frozen_access(this);
      return this[ivar] = val;
    }
  }
  Opal.assign_ivar_val = function(ivar, static_val) {
    return function() {
      $deny_frozen_access(this);
      return this[ivar] = static_val;
    }
  }

  // Primitives for handling parameters
  Opal.ensure_kwargs = function(kwargs) {
    if (kwargs == null) {
      return new Map();
    } else if (kwargs.$$is_hash) {
      return kwargs;
    } else {
      $raise(Opal.ArgumentError, 'expected kwargs');
    }
  }

  Opal.get_kwarg = function(kwargs, key) {
    var kwarg = Opal.hash_get(kwargs, key);
    if (kwarg === undefined) {
      $raise(Opal.ArgumentError, 'missing keyword: '+key);
    }
    return kwarg;
  }

  // Arrays of size > 32 elements that contain only strings,
  // symbols, integers and nils are compiled as a self-extracting
  // string.
  Opal.large_array_unpack = function(str) {
    var array = str.split(","), length = array.length, i;
    for (i = 0; i < length; i++) {
      switch(array[i][0]) {
        case undefined:
          array[i] = nil
          break;
        case '-':
        case '0':
        case '1':
        case '2':
        case '3':
        case '4':
        case '5':
        case '6':
        case '7':
        case '8':
        case '9':
          array[i] = +array[i];
      }
    }
    return array;
  }

  // Opal32-checksum algorithm for #hash
  // -----------------------------------
  Opal.opal32_init = $return_val(0x4f70616c);

  function $opal32_ror(n, d) {
    return (n << d)|(n >>> (32 - d));
  };

  Opal.opal32_add = function(hash, next) {
    hash ^= next;
    hash = $opal32_ror(hash, 1);
    return hash;
  };

  // Initialization
  // --------------
  Opal.BasicObject = BasicObject = $allocate_class('BasicObject', null);
  Opal.Object      = _Object     = $allocate_class('Object', Opal.BasicObject);
  Opal.Module      = Module      = $allocate_class('Module', Opal.Object);
  Opal.Class       = Class       = $allocate_class('Class', Opal.Module);
  Opal.Opal        = _Opal       = $allocate_module('Opal');
  Opal.Kernel      = Kernel      = $allocate_module('Kernel');

  $set_proto(Opal.BasicObject, Opal.Class.$$prototype);
  $set_proto(Opal.Object, Opal.Class.$$prototype);
  $set_proto(Opal.Module, Opal.Class.$$prototype);
  $set_proto(Opal.Class, Opal.Class.$$prototype);

  // BasicObject can reach itself, avoid const_set to skip the $$base_module logic
  BasicObject.$$const.BasicObject = BasicObject;

  // Assign basic constants
  $const_set(_Object, "BasicObject",  BasicObject);
  $const_set(_Object, "Object",       _Object);
  $const_set(_Object, "Module",       Module);
  $const_set(_Object, "Class",        Class);
  $const_set(_Object, "Opal",         _Opal);
  $const_set(_Object, "Kernel",       Kernel);

  // Fix booted classes to have correct .class value
  BasicObject.$$class = Class;
  _Object.$$class     = Class;
  Module.$$class      = Class;
  Class.$$class       = Class;
  _Opal.$$class       = Module;
  Kernel.$$class      = Module;

  // Forward .toString() to #to_s
  $prop(_Object.$$prototype, 'toString', function() {
    var to_s = this.$to_s();
    if (to_s.$$is_string && typeof(to_s) === 'object') {
      // a string created using new String('string')
      return to_s.valueOf();
    } else {
      return to_s;
    }
  });

  // Make Kernel#require immediately available as it's needed to require all the
  // other corelib files.
  $prop(_Object.$$prototype, '$require', Opal.require);

  // Instantiate the main object
  Opal.top = new _Object();
  Opal.top.$to_s = Opal.top.$inspect = $return_val('main');
  Opal.top.$define_method = top_define_method;

  // Foward calls to define_method on the top object to Object
  function top_define_method() {
    var block = top_define_method.$$p;
    top_define_method.$$p = null;
    return Opal.send(_Object, 'define_method', arguments, block)
  };

  // Nil
  Opal.NilClass = $allocate_class('NilClass', Opal.Object);
  $const_set(_Object, 'NilClass', Opal.NilClass);
  nil = Opal.nil = new Opal.NilClass();
  nil.$$id = nil_id;
  nil.call = nil.apply = function() { $raise(Opal.LocalJumpError, 'no block given'); };
  nil.$$frozen = true;
  nil.$$comparable = false;
  Object.seal(nil);

  Opal.thrower = function(type) {
    var thrower = {
      $thrower_type: type,
      $throw: function(value, called_from_lambda) {
        if (value == null) value = nil;
        if (this.is_orphan && !called_from_lambda) {
          $raise(Opal.LocalJumpError, 'unexpected ' + type, value, type.$to_sym());
        }
        this.$v = value;
        throw this;
      },
      is_orphan: false
    }
    return thrower;
  };

  // Define a "$@" global variable, which would compute and return a backtrace on demand.
  Object.defineProperty($gvars, "@", {
    enumerable: true,
    configurable: true,
    get: function() {
      if ($truthy($gvars["!"])) return $gvars["!"].$backtrace();
      return nil;
    },
    set: function(bt) {
      if ($truthy($gvars["!"]))
        $gvars["!"].$set_backtrace(bt);
      else
        $raise(Opal.ArgumentError, "$! not set");
    }
  });

  Opal.t_eval_return = Opal.thrower("return");

  TypeError.$$super = Error;

  // If enable-file-source-embed compiler option is enabled, each module loaded will add its
  // sources to this object
  Opal.file_sources = {};
}).call(this);