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  • forwardable.rb

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Forwardable

The Forwardable module provides delegation of specified methods to a designated object, using the methods def_delegator and def_delegators.

For example, say you have a class RecordCollection which contains an array @records. You could provide the lookup method record_number(), which simply calls [] on the @records array, like this:

class RecordCollection
  extend Forwardable
  def_delegator :@records, :[], :record_number
end

Further, if you wish to provide the methods size, <<, and map, all of which delegate to @records, this is how you can do it:

class RecordCollection
  # extend Forwardable, but we did that above
  def_delegators :@records, :size, :<<, :map
end

Also see the example at forwardable.rb.

Attributes

debug[RW]

force Forwardable to show up in stack backtraces of delegated methods

Public Instance Methods

def_delegator(accessor, method, ali = method) click to toggle source
Alias for: def_instance_delegator
def_delegators(accessor, *methods) click to toggle source
Alias for: def_instance_delegators
def_instance_delegator(accessor, method, ali = method) click to toggle source

Defines a method method which delegates to obj (i.e. it calls the method of the same name in obj). If new_name is provided, it is used as the name for the delegate method.

See the examples at Forwardable and forwardable.rb.

 
               # File forwardable.rb, line 143
  def def_instance_delegator(accessor, method, ali = method)
    accessor = accessor.id2name if accessor.kind_of?(Integer)
    method = method.id2name if method.kind_of?(Integer)
    ali = ali.id2name if ali.kind_of?(Integer)

    module_eval(<<-EOS, "(__FORWARDABLE__)", 1)
      def #{ali}(*args, &block)
        begin
          #{accessor}.__send__(:#{method}, *args, &block)
        rescue Exception
          $@.delete_if{|s| /^\\(__FORWARDABLE__\\):/ =~ s} unless Forwardable::debug
          Kernel::raise
        end
      end
    EOS
  end
Also aliased as: def_delegator
def_instance_delegators(accessor, *methods) click to toggle source

Shortcut for defining multiple delegator methods, but with no provision for using a different name. The following two code samples have the same effect:

def_delegators :@records, :size, :<<, :map

def_delegator :@records, :size
def_delegator :@records, :<<
def_delegator :@records, :map

See the examples at Forwardable and forwardable.rb.

 
               # File forwardable.rb, line 130
def def_instance_delegators(accessor, *methods)
  for method in methods
    def_instance_delegator(accessor, method)
  end
end
Also aliased as: def_delegators