From: Robert Klemme <shortcutter@...>
Date: 2007-09-03T14:55:04+09:00
Subject: Re: Hash.new with a block?

On 03.09.2007 06:50, 7stud -- wrote:
> In the code:
> 
> h = Hash.new {|hash, key| hash[key] = []}
> 
> what method is yielding the values hash, key to the code block?  It
> doesn't seem like it could be new() since new() isn't called when you
> lookup a key in a hash.  Does new() somehow associate that block with
> the method [] in Hash?

$ ruby -e 'h=Hash.new {|h,k| h[k]=[]}; set_trace_func(lambda {|*a| p 
a}); h[1]<<2'
["line", "-e", 1, nil, #<Binding:0x1002fdf4>, false]
["c-call", "-e", 1, :[], #<Binding:0x1002fdb8>, Hash]
["c-call", "-e", 1, :default, #<Binding:0x1002fca0>, Hash]
["c-call", "-e", 1, :call, #<Binding:0x1002fb9c>, Proc]
["line", "-e", 1, nil, #<Binding:0x1002f9a8>, false]
["c-call", "-e", 1, :[]=, #<Binding:0x1002f8a4>, Hash]
["c-return", "-e", 1, :[]=, #<Binding:0x1002f868>, Hash]
["c-return", "-e", 1, :call, #<Binding:0x1002f778>, Proc]
["c-return", "-e", 1, :default, #<Binding:0x1002f688>, Hash]
["c-return", "-e", 1, :[], #<Binding:0x1002f598>, Hash]
["c-call", "-e", 1, :<<, #<Binding:0x1002f4a8>, Array]
["c-return", "-e", 1, :<<, #<Binding:0x1002f3b8>, Array]

I believe there's also some explanation in the documentation.

Kind regards

	robert