ruby / forwardable

Provides delegation of specified methods to a designated object

Forwardable

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

Installation

Add this line to your application's Gemfile:

gem 'forwardable'

And then execute:

$ bundle

Or install it yourself as:

$ gem install forwardable

Usage

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:

  require 'forwardable'

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

We can use the lookup method like so:

  r = RecordCollection.new
  r.records = [4,5,6]
  r.record_number(0)  # => 4

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 # re-open RecordCollection class
    def_delegators :@records, :size, :<<, :map
  end

  r = RecordCollection.new
  r.records = [1,2,3]
  r.record_number(0)   # => 1
  r.size               # => 3
  r << 4               # => [1, 2, 3, 4]
  r.map { |x| x * 2 }  # => [2, 4, 6, 8]

You can even extend regular objects with Forwardable.

  my_hash = Hash.new
  my_hash.extend Forwardable              # prepare object for delegation
  my_hash.def_delegator "STDOUT", "puts"  # add delegation for STDOUT.puts()
  my_hash.puts "Howdy!"

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/ruby/forwardable.

License

The gem is available as open source under the terms of the 2-Clause BSD License.

forwardable's Issues

def_*_delegator from v1.3.0 does not return name of delegator method in Ruby 2.6 and older

In v1.2.0, def_delegator :@obj, :data, :fallback_data would return :fallback_data but v1.3.0 just returns nil

The cause for this is the last expression mod.send(:ruby2_keywords, ali) if RUBY_VERSION >= '2.7' in the following definition:

forwardable/lib/forwardable.rb

Lines 182 to 189 in e56f0f8

	def def_instance_delegator(accessor, method, ali = method)
	gen = Forwardable._delegator_method(self, accessor, method, ali)
	# If it's not a class or module, it's an instance
	mod = Module === self ? self : singleton_class
	mod.module_eval(&gen)
	mod.send(:ruby2_keywords, ali) if RUBY_VERSION >= '2.7'
	end

The last expression is evaluated only if RUBY_VERSION >= '2.7'.
The preferred solution would be to stash the result of the previous expression and return that stashed value for Ruby 2.6 and older:

 def def_instance_delegator(accessor, method, ali = method)
   gen = Forwardable._delegator_method(self, accessor, method, ali)

   # If it's not a class or module, it's an instance
   mod = Module === self ? self : singleton_class

   # stash in a lvar
   result = mod.module_eval(&gen)
   RUBY_VERSION >= '2.7' ? mod.send(:ruby2_keywords, ali) : result
 end

Based on the diff of #5, this issue would affect :single_delegator as well.

/cc @jeremyevans @hsbt Requesting a patch to be shipped at the earliest.
Thank you.

Add CI ?

would be nice if PRs had automated testing

Say if this is the official repo or a mirror

Using the last argument as keyword parameters is deprecated; maybe ** should be added to the call

Hello.

I see ruby2_keywords usage, but I'm getting such warnings for some reason in my project:

/home/alex/Projects/ruby/forwardable/lib/forwardable.rb:238: warning: Using the last argument as keyword parameters is deprecated; maybe ** should be added to the call
/home/alex/.rbenv/versions/2.7.1/lib/ruby/gems/2.7.0/gems/ferrum-0.9/lib/ferrum/page/screenshot.rb:35: warning: The called method `pdf' is defined here

ruby 2.7.1p83 (2020-03-31 revision a0c7c23c9c) [x86_64-linux]

I see this referenced source: https://github.com/rubycdp/ferrum/blob/6906d98/lib/ferrum/page/screenshot.rb#L35

def pdf(**opts)

What changes are expected and where?

already initialized constant Forwardable::FORWARDABLE_VERSION

Hi at forwardable,

You might want to fix this one:

/usr/local/lib/ruby/gems/2.6.0/gems/forwardable-1.3.1/lib/forwardable/version.rb:3: warning: previous definition of VERSION was here
/usr/local/lib/ruby/2.6.0/forwardable.rb:117: warning: already initialized constant Forwardable::FORWARDABLE_VERSION

It actually is the last gem in my bundle
that gives me a warning message like that.
All the other gems cleaned that up already.

Let's bring this forward!