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 f = Foo.new f.printf ... f.gets f.content_at(1)
Also see the example at forwardable.rb.
# File forwardable.rb, line 178 def def_instance_delegator(accessor, method, ali = method) line_no = __LINE__; str = %{ 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 } # If it's not a class or module, it's an instance begin module_eval(str, __FILE__, line_no) rescue instance_eval(str, __FILE__, line_no) end end
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
# File forwardable.rb, line 170 def def_instance_delegators(accessor, *methods) methods.delete("__send__") methods.delete("__id__") for method in methods def_instance_delegator(accessor, method) end end
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.
# File forwardable.rb, line 150 def instance_delegate(hash) hash.each{ |methods, accessor| methods = methods.to_s unless methods.respond_to?(:each) methods.each{ |method| def_instance_delegator(accessor, method) } } end