From: Trans <transfire@...>
Date: 2005-10-26T02:02:03+09:00
Subject: Re: Meta methods to govern meta data?


Duane Johnson wrote:
> I was intrigued by one of Matz's "Wild and Crazy Ideas" at RubyConf--
> the inclusion of meta data in the comments section before a method
> definition.
>
> This got me thinking about the need for metadata and Ruby's fabulous
> introspective capabilities and I wondered if it might be better to
> have a governing "metamethod" for each method.  Actually, more like
> accessor metamethods.  These metamethods would be in charge of
> setting or getting key/value pairs describing things about the method
> it is associated with:
>
> # Returns double the input
> def double(i)
>      i * 2
> end
>
> meta :double, :require => 'i.is_a? Fixnum'
> meta :double, :comments
> => 'Returns double the input'

See Facets annotation.rb. And I would urge you to call them annotations
and not metadata. metadata is more apt to describing langauge reflexion
and in general is too generic a terminology.

> I don't quite like the syntax yet, (probably because we don't really
> have a facility yet to talk about methods like this); however, I do
> like the flexibility provided.  Perhaps we could make a new syntax
> like this:
>
> def double>require(i)
>      i.is_a? Fixnum
> end
>
> def double>comment(original_comment)
>      "Haha! I can over-ride the comment."
> end
>
> And we could even do some cool stuff like custom namespace selectors:
>
> def double>visibility(looking_at_me)
>      [Object, ActiveRecord].include? looking_at_me
> end
>
> (i.e. the method would be called prior to any reference to 'double'
> and it would return 'true' if it is visible from within the caller's
> scope / namespace).
>
> We could even talk about meta-metamethods:
>
> def double>visibility>comment
>      "Comment for the 'double>visibility' metamethod"
> end

I fear more syntax.

T.