Contents

module Tap
  module Support
    
    # Generates an Intern module to override the specified method_name.  Intern
    # modules are useful to override a tiny bit of functionality without having
    # to generate a full subclass.
    #
    # An Intern module:
    #
    # - adds an accessor for <method_name>_block
    # - overrides <method_name> to call the block, prepending self to
    #   the input arguments
    #
    # For example:
    #
    #   array = [1,2,3].extend Intern(:last)
    #
    #   array.last             # => 3
    #   array.last_block = lambda {|arr| arr.first }
    #   array.last             # => 3
    #
    def self.Intern(method_name)
      mod = INTERN_MODULES[method_name.to_sym]
      return mod unless mod == nil

      mod = INTERN_MODULES[method_name.to_sym] = Module.new
      mod.module_eval %Q{
      attr_accessor :#{method_name}_block

      def #{method_name}(*inputs)
        return super unless #{method_name}_block
        inputs.unshift(self)

        arity = #{method_name}_block.arity
        n = inputs.length
        unless n == arity || (arity < 0 && (-1-n) <= arity) 
          raise ArgumentError.new("wrong number of arguments (\#{n} for \#{arity})")
        end

        #{method_name}_block.call(*inputs)
      end
      }
      mod
    end
    
    # An array of already-declared intern modules,
    # keyed by method_name.
    INTERN_MODULES = {}
    
    # An Intern module for :process.
    Intern = Support.Intern(:process)
  end
end

Version data entries

2 entries across 2 versions & 1 rubygems

Version	Path
tap-0.17.1	lib/tap/support/intern.rb
tap-0.17.0	lib/tap/support/intern.rb