Usage of The SingleForwardable is like Fowadable module.

Methods
D
S
Instance Public methods
def_delegator(accessor, method, ali = method)
Alias for: def_single_delegator
def_delegators(accessor, *methods)
Alias for: def_single_delegators
def_single_delegator(accessor, method, ali = method)

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.

Also aliased as: def_delegator

Source: show | on GitHub 

# File ../ruby/lib/forwardable.rb, line 267
def def_single_delegator(accessor, method, ali = method)
  str = %Q{
    def #{ali}(*args, &block)
      begin
        #{accessor}.__send__(:#{method}, *args, &block)
      rescue Exception
        $@.delete_if{|s| %r"#{Regexp.quote(__FILE__)}"o =~ s} unless Forwardable::debug
        ::Kernel::raise
      end
    end
  }

  instance_eval(str, __FILE__, __LINE__)
end
def_single_delegators(accessor, *methods)

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
Also aliased as: def_delegators

Source: show | on GitHub 

# File ../ruby/lib/forwardable.rb, line 254
def def_single_delegators(accessor, *methods)
  methods.delete("__send__")
  methods.delete("__id__")
  for method in methods
    def_single_delegator(accessor, method)
  end
end
delegate(hash)
Alias for: single_delegate
delegate method => accessor delegate [method, method, ...] => accessor

Takes a hash as its argument. The key is a symbol or an array of symbols. These symbols correspond to method names. The value is the accessor to which the methods will be delegated.

Also aliased as: delegate

Source: show | on GitHub 

# File ../ruby/lib/forwardable.rb, line 234
def single_delegate(hash)
  hash.each{ |methods, accessor|
    methods = [methods] unless methods.respond_to?(:each)
    methods.each{ |method|
      def_single_delegator(accessor, method)
    }
  }
end