From: Julian Leviston <julian@...>
Date: 2013-03-30T00:45:07+09:00
Subject: Re: Hash with default

On 29/03/2013, at 8:32 PM, Harry Kakueki <list.push@gmail.com> wrote:

> I would like to make a hash like h2 with the default described by h in one line when I create the hash instead of 3 lines and 2 hashes like I did here.
> Any ideas?
> 
> h = Hash.new {|x,y| x[y] = y}
> h2 = {"two"=>2,"three"=>3}
> h.merge!(h2)
> p h["two"]     #> 2
> p h["tree"]    #> "tree"
> 
> 
> 
> Harry
> 


You *can* set a default... but you can't set the default to be a piece of code that can change default behaviour. By the way, the first line of your program doesn't work. You know that, right?

To get what you want, you can do this:

h = {}; def h.[](key); self.has_key?(key) ? super(key) : key; end

or alternatively:

h = {}
(class << h; self; end).send(:define_method, :[]){|key| self.has_key?(key) ? super(key) : key}

Julian