From: Daniel Sheppard <daniels@...>
Date: 2005-10-27T15:32:25+09:00
Subject: Re: Meta methods to govern meta data?

The following is an implementation I just whipped up of annotation.

- annotations are cascaded up through superclasses.
- no way to remove an annotation (could override with a nil value
though...)
- allows you to use this syntax:

    class Dude
        annotate :a => :b
        def get_jiggy
        end
    end

  to annotate the method, which I think is much nicer than "annotate
:get_jiggy, :a => :b", though that
  method is also available. This, however introduces a dependency on
method_added not being overridden which
  I don't know how to avoid.

-----

class Module
    def annotate(*args)
        hash = 
        case args.length
            when 2: 
                annotation_hash[args[0]].update(args[1])
            when 1: 
                x = class_eval("@@__meta_next_update ||= {}")
                x.update(args[0])
            else
                raise ArgumentError, "wrong number of arguments
(#{args.length})"
        end
    end
    def annotation_hash
        class_eval("@@__meta ||= Hash.new {|h,k| h[k]={}}")
    end
    private :annotation_hash
    def annotations(symbol)
        symbol = symbol.intern unless Symbol === symbol
        my_hash = annotation_hash[symbol]
        my_hash = superclass.annotations(symbol).merge(my_hash) if
superclass
        my_hash
    end
    #it's nice to be able to annotate without naming the method (just
apply it to the next method added) 
    def method_added(symbol)
        meta_hash = annotation_hash[symbol]
        new_hash = class_eval("x = @@__meta_next_update||=nil;
@@__meta_next_update = nil;x")
        meta_hash.update(new_hash) if new_hash
    end
end
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