From: Paul Brannan <paul@...>
Date: 2002-04-10T23:04:07+09:00
Subject: Re: mix-in dependancy

On Wed, Apr 10, 2002 at 10:36:52AM +0900, Yohanes Santoso wrote:
> What I want is for the including to fail if A does not have #<=>. Is
> there a built-in mechanism to detect this or should I do this
> manually:

I know of no built-in mechanism.  However, RubyTreasures has something
for this:

  http://rm-f.net/~cout/ruby/treasures/RubyTreasures-0.3/lib/hacks/safe_mixin.rb.html

  require 'rbt/hacks/safe_mixin'

  module Sort
    mixin_requires :<=>
  end

  class A
  end

  A.class_eval { include Sort } #=> RuntimeError: Module A does not defined method <=>

(the current version of RubyTreasures raises a RuntimeError.  The next version may raise a TypeError).

Paul