From: Adam Prescott <adam@...>
Date: 2013-03-30T01:02:40+09:00
Subject: Re: Hash with default

On 29 March 2013 15:53, Julian Leviston <julian@coretech.net.au> wrote:
>  h = {"two"=>2,"three"=>3}; def h.[](key); self.has_key?(key) ? super(key) : key; end

Why not use the block to Hash.new instead of overriding #[] ?

>> h = Hash.new { |h,k| k }
=> {}
>> h["one"]
=> "one"
>> h
=> {}

Note this is different than using h[k] = k in the block.

As for the original question, I think you can rely on default_proc and
get around the fact it doesn't return the receiver pretty easily.

>> h = { "two" => 2, "three" => 3 }.tap { |o| o.default_proc = lambda { |h, k| k } }
=> {"two"=>2, "three"=>3}
>> h
=> {"two"=>2, "three"=>3}
>> h["two"]
=> 2
>> h["five"]
=> "five"
>> h
=> {"two"=>2, "three"=>3}

Having said that, I don't see any benefit in trying to get it down to
a single line and sacrificing readability. You can define h to be what
you want, then on a separate line just call #default_proc=.