From: Gavin Sinclair <gsinclair@...>
Date: 2003-11-22T15:19:33+09:00
Subject: Method wrapper question (was "stereotyping (was ...))

On Saturday, November 22, 2003, 10:53:39 AM, Yukihiro wrote:

[On how one might 'implement' interfaces:]

> I prefer Jim Weirich's idea in [ruby-talk:86007], utilizing method
> combination.

> in the library code foo.rb:

>   require 'foo_if'
>   # which defines interface
>   # you can comment out from production code

>   class Foo
>     def greet(hi)
>       hi.display
>       print "\n"
>     end
>   end

> in the foo_if.rb:

>   class Foo
>     def greet:pre(hi)
>       assert hi.respond_to? :display
>     end
>   end


> with probably interface checking cosmetic.


I'm not buying into the interface debate one way or the other, but a
related question here is: how do you envisage :pre, :post, etc.,
working if they are defined multiple times?

This is important because they could be used to implement some
aspect-oriented code, and then also be used to implement some
interface checking.

For example:

  class Example
    def meth(o)
      # some code on 'o'
    end

    def meth:pre(o)
      logger.info "About to process #{o}"
    end

    def meth:pre(o)
      assert o.responds_to? :display
    end
  end


Do both the :pre method wrappers get executed?  If so, in what order?
If not, which one does?  And why not execute both?

Gavin