From: Daniel DeLorme <dan-ml@...42.com>
Date: 2007-06-16T12:19:27+09:00
Subject: Re: Using extend for initialization settings?

Trans wrote:
>   M = { :a => 1 }.to_module(true)
>   p M.a  #=> 1
> 
> 
>   class Foo
>     def initialize( settings )
>       extend settings.to_module
>     end
>   end
> 
>   f = Foo.new(:x => 9)
>   p f.x  #=> 9
> 
> 
> Thoughts?

The behavior is substantially different. With hash initialization, 
reader and writer accessors are defined in the class. With this 
technique it seems there's only a reader accessor, and it is only 
defined per object. What methods the object responds to depend on the 
initialization values.

In effect this seems to create per-object constants rather than 
traditional "attributes". Maybe I can express myself better with code:

class Foo
   attr_accessor :a, :b
end
h = Foo.new(:a=>1)
h.a   #=> 1
h.a=2 #=> 2
h.b   #=> nil
h.c   #=> NoMethodError
m = Foo.new(:a=>1) #using to_module
m.a   #=> 1
m.a=2 #=> NoMethodError
m.b   #=> NoMethodError
m.c   #=> NoMethodError
s = OpenStruct.new(:a=>1)
s.a   #=> 1
s.a=2 #=> 2
s.b   #=> nil
s.c   #=> nil

If you can find a use for such behavior then it's fine, but I'm afraid I 
can't.

Daniel