From: Carl <carl.baldwin@...>
Date: 2005-04-19T00:54:37+09:00
Subject: Undocumented behavior related to Hash::default_proc

Hello,

I found a behavior in Ruby 1.8.2 in using Hashes with a default_proc.
Here is what I did:

def initialize
  @var = Hash.new { |hash,key| hash[key] = Array.new }
  ...
  elements.each { |element|
    ...
    @var[key].push element
    ...
  }
  ...

I like that I can make this Hash autovivifying (somewhat like Perl) for
this initial loop.  It made the loop more concise.  However, I also
like that in Ruby, I can 'turn it off' when I'm done.  After the above
iterator executes I do this:

  @var.default = nil

At least in Ruby 1.8.2 this line makes the default_proc effectively go
away.

The problem is that I cannot find any documentation for Hash that
explicitly states this as the behavior of hash.default = nil.

My fear is that someday down the road this undocumented behavior will
go away or change.    Since Hash does not implement default_proc= to
explicitly assign the default_proc this is the only way to accomplish
what I want to do.  I would recommend one of the following:

1 - Document this behavior and keep it for good.
2 - Implement default_proc= and allow hash.default_proc = nil to
accomplish this.
3 - Come up with a better way to allow 'turning off' the default_proc
and document it.

Thoughts?

Thank you,
Carl