From: Paul Brannan <pbrannan@...>
Date: 2001-11-30T07:29:00+09:00
Subject: [ruby-talk:26980] Re: thoughts on virtual base classes, interfaces

On Fri, Nov 30, 2001 at 07:15:28AM +0900, MikkelFJ wrote:

> The above problem is exactly what would elegantly be handled by first class
> functions. You'd just pass the run function directly instead of having to
> create an object that respond to some named function like "run". If more
> functions that run were desired, it might be better to create a class, or a
> list of functions could be passed in a hashtable.

In Ruby, I can do this:
  def foo(fun)
    fun.call()
  end

  def bar()
    puts "foo!"
  end

  foo(Object.method(:bar))  #=> foo!

Or, I can do this:
  x = 42
  foo proc {
    puts x
  }                         #=> 42

The problem is not that Ruby does not have first-class functions, but
that Ruby makes a distinction between a method and a callable object.
IMO, this is not really a problem at all, but actually provides clarity
(I've been bitten many times in Python by writing x = foo instead of x =
foo()).

On a side note, you can do similar things in C++ with the "lambda library"
(http://lambda.cs.utu.fi/).  I've never used it, but it looks pretty
cool.

Paul