From: Ben Bleything <ben@...>
Date: 2007-07-20T07:53:17+09:00
Subject: Re: Hash of arrays - whats going on?

On Fri, Jul 20, 2007, stephen O'D wrote:
> So my problem is solved, but why do you have to do it like this?  At
> the risk of answering my own question, is it because the block is re-
> executed everytime you access a non existent key, creating a brand new
> array object, while the first way, it just initialises the value to
> the same array each time?

The default value you provide is a reference... in this case, you say
"use this array as the default value", not "use an empty array as a
default value".  To see what I mean, try this:

    empty_ary = []
    h = Hash.new
    h.default = empty_ary

    h['foo'] << 10
    puts empty_ary.size

    h[foo'] << 20
    puts empty_ary.size

    h['bar'] << 23
    puts empty_ary.size

    h['bar'] << 33
    puts empty_ary.size

That should show you what's happening.

Ben