lib/bindata/base.rb in bindata-0.6.0 vs lib/bindata/base.rb in bindata-0.7.0

@@ -12,15 +12,17 @@
   # Parameters may be provided at initialisation to control the behaviour of
   # an object.  These params are:
   #
   # [<tt>:readwrite</tt>]     If false, calls to #read or #write will
   #                           not perform any I/O.  Default is true.
-  # [<tt>:check_offset</tt>]  Raise an error if the current IO offest doesn't
+  # [<tt>:check_offset</tt>]  Raise an error if the current IO offset doesn't
   #                           meet this criteria.  A boolean return indicates
   #                           success or failure.  Any other return is compared
-  #                           to the current offset.  This parameter is
-  #                           only checked before reading.
+  #                           to the current offset.  The variable +offset+
+  #                           is made available to any lambda assigned to
+  #                           this parameter.  This parameter is only checked
+  #                           before reading.
   class Base
     class << self
       # Returns the mandatory parameters used by this class.  Any given args
       # are appended to the parameters list.  The parameters for a class will
       # include the parameters of its ancestors.
@@ -31,11 +33,11 @@
             if parent.respond_to?(:mandatory_parameters)
               @mandatory_parameters.concat(parent.mandatory_parameters)
             end
           end
         end
-        unless (args.empty?)
+        if not args.empty?
           args.each { |arg| @mandatory_parameters << arg.to_sym }
           @mandatory_parameters.uniq!
         end
         @mandatory_parameters
       end
@@ -51,11 +53,11 @@
             if parent.respond_to?(:optional_parameters)
               @optional_parameters.concat(parent.optional_parameters)
             end
           end
         end
-        unless (args.empty?)
+        if not args.empty?
           args.each { |arg| @optional_parameters << arg.to_sym }
           @optional_parameters.uniq!
         end
         @optional_parameters
       end
@@ -109,18 +111,18 @@
     # +params+ is a hash containing symbol keys.  Some params may
     # reference callable objects (methods or procs).  +env+ is the
     # environment that these callable objects are evaluated in.
     def initialize(params = {}, env = nil)
       # default :readwrite param to true if unspecified
-      unless params.has_key?(:readwrite)
+      if not params.has_key?(:readwrite)
         params = params.dup
         params[:readwrite] = true
       end
 
       # ensure mandatory parameters exist
       self.class.mandatory_parameters.each do |prm|
-        unless params.has_key?(prm)
+        if not params.has_key?(prm)
           raise ArgumentError, "parameter ':#{prm}' must be specified " +
                                "in #{self}"
         end
       end
 
@@ -195,13 +197,14 @@
       LazyEvalEnv.new(@env)
     end
 
     # Returns the value of the evaluated parameter.  +key+ references a
     # parameter from the +params+ hash used when creating the data object.
+    # +values+ contains data that may be accessed when evaluating +key+.
     # Returns nil if +key+ does not refer to any parameter.
-    def eval_param(key)
-      @env.lazy_eval(@params[key])
+    def eval_param(key, values = {})
+      @env.lazy_eval(@params[key], values)
     end
 
     # Returns the parameter from the +params+ hash referenced by +key+.
     # Use this method if you are sure the parameter is not to be evaluated.
     # You most likely want #eval_param.
@@ -225,16 +228,16 @@
 
     # Checks that the current offset of +io+ is as expected.  This should
     # be called from #do_read before performing the reading.
     def check_offset(io)
       if has_param?(:check_offset)
-        @env.offset = io.pos - io.mark
-        expected = eval_param(:check_offset)
+        actual_offset = io.pos - io.mark
+        expected = eval_param(:check_offset, :offset => actual_offset)
 
         if not expected
           raise ValidityError, "offset not as expected"
-        elsif @env.offset != expected and expected != true
-          raise ValidityError, "offset is '#{@env.offset}' but " +
+        elsif actual_offset != expected and expected != true
+          raise ValidityError, "offset is '#{actual_offset}' but " +
                                "expected '#{expected}'"
         end
       end
     end