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] unless methods.respond_to?(:each)
methods.each{ |method|
def_instance_delegator(accessor, method)
}
}
end