Module: Forwardable

Defined in:
lib/forwardable.rb

Overview

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.

Class Attribute Summary collapse

Instance Method Summary collapse

Class Attribute Details

.debug ⇒ Object

force Forwardable to show up in stack backtraces of delegated methods



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# File 'lib/forwardable.rb', line 114

def debug
  @debug
end

Instance Method Details

#def_instance_delegator(accessor, method, ali = method) ⇒ Object Also known as: def_delegator

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.



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# File 'lib/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
 [email protected]_if{|s| /^\\(__FORWARDABLE__\\):/ =~ s} unless Forwardable::debug
 Kernel::raise
	end
    end
  EOS
end

#def_instance_delegators(accessor, *methods) ⇒ Object Also known as: def_delegators

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.



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# File 'lib/forwardable.rb', line 130

def def_instance_delegators(accessor, *methods)
  for method in methods
    def_instance_delegator(accessor, method)
  end
end