Issue #6594 has been updated by prijutme4ty (Ilya Vorontsov).


I agree that high-order messaging can be very useful. But functor concept and usage is rather complex that makes it hard to understand in which real cases it's useful (where one can't stick to another way to do the same thing). Can you provide really cool usage of functor class?
If you want to easy build constructs like: 
[0,1,2,3,4].having.succ < 3 (from article you mentioned),
I suggest you simplier way of doing so (my realization of such behavior https://github.com/prijutme4ty/bioinform/blob/master/lib/bioinform/support/callable_symbol.rb):
[0,1,2,3,4].select(&:succ.() < 3)
or even so:
256.times.select(&:to_s.(2).size == 4)    # ==> [8,9,10,11,12,13,14,15]

and I can chain any calls in proc without any additional code for selectors etc. It's also HOM, of course. I hope one day Matz would eliminate dot before brackets of call method - then syntax'd be even more concise.
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Feature #6594: Integrated Functor
https://bugs.ruby-lang.org/issues/6594#change-27284

Author: trans (Thomas Sawyer)
Status: Open
Priority: Normal
Assignee: 
Category: core
Target version: 2.0.0


=begin
I know the developers meeting is coming up so I'd like to get a few ideas I've had sitting in the wings out in the air before then.

One the more useful is the idea of integrating Functors directly into the language. "Functor" is the term I use for "higher-order function".

I blogged about this idea and you can read it here: http://trans.github.com/2011-09-07-ruby-heart-higher-order-functions/

The super short version is this:

  def f => op, arg
    arg.send(__op__, arg)
  end

  f + 3  #=> 6
  f * 3  #=> 9

Another example:

  class String
    def file => op, *args
      File.send(__op__, self, *args)
    end
  end

  "README.rdoc".file.mtime  #=> 2012-06-14 12:34:45 -0400

I'm using `=>` as means of indicating a higher-order function. Of course another syntax could be used if this won't fly. The important thing is the idea of higher-order functions being integrated directly into the language. Doing this without that integration requires the creation of an intermediate object for each call which is very inefficient.
=end



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