From: ES <ruby-ml@...>
Date: 2005-03-13T04:31:37+09:00
Subject: Re: Ruby black magic? Meta Programming

On Sat, March 12, 2005 7:11 pm, Tom Willis said:
> My first exposure to Ruby was from Jim, and his "10 things every java
> programmer should know about ruby" presentation.
>
> Anyway, I probably shouldn't even be thinking about this kind of stuff
> yet, but one thing in the presentation that I dug a lot was the use of
> overriding Kernel#method_missing to queue messages and play them back
> in order.
>
> Anyway, I want to know what other kind of cool,i guess I'll call it
> metaprogramming, can be done in ruby.
>
>
> For example, I remember reading something about Eiffel having the
> ability to declare pre and post conditions for method calls on
> objects, essentially bringing this criteria in as part of the
> interface. Can something like this be done in Ruby? I'm assuming so,
> but for some reason my google hits keep referring me to Pyhon's
> Metaclass things, go figure.
>
> Anyone got a link?

Currently pre/postconditions are proposed for Ruby 2.0, see\
http://www.rubygarden.org/ruby?Rite

You can achieve the same effect by creating a meta for something like
def_pre :methodname, def_post :methodname with associated blocks. Then
alias the actual :methodname, make the pre block respond to :methodname;
pre executes its block and then calls :methodname, after which post block
is called.

> Thomas G. Willis

E