From: Julian Leviston <julian@...>
Date: 2013-03-30T00:53:33+09:00
Subject: Re: Hash with default



On 30/03/2013, at 2:45 AM, Julian Leviston <julian@coretech.net.au> wrote:

> 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



Sorry, forgot to set your data in there, too:

 h = {"two"=>2,"three"=>3}; def h.[](key); self.has_key?(key) ? super(key) : key; end

There you go. Not really on one line, but oh well, you wanted different behaviour than the default hash behaviour for defaults.

Julian