From: RichardOnRails <RichardDummyMailbox58407@...>
Date: 2011-01-24T04:20:53+09:00
Subject: Re: Easiest way in Ruby to express "given this, set target to this if nil or undefined, else increment by this"

On Jan 23, 11:10 am, yermej <yer...@gmail.com> wrote:
> On Jan 22, 10:50 pm, RichardOnRails
>
> <RichardDummyMailbox58...@USComputerGurus.com> wrote:
> > class Z
> >     def self.show_z
> >         @@zz ||= 0; @@zz += 1
> >         puts @@zz
> >     end
> > end
> > Z.show_z        # => 1
> > Z.show_z        # => 2
>
> The singleton pattern works well for this sort of thing.
>
> require 'singleton' # this is part of Ruby's standard library
> class Counter
>   include Singleton
>   def count
>     @count = (@count ? @count + 1 : 0)
>   end
> end
>
> a = Counter.instance
> a.count # => 0
> a.count # => 1
> b = Counter.instance
> b.count # => 2
>
> > $h = Hash.new(:y)
> > def show_y
> >     $h[:y] ||= 0; $h[:y] += 1 # => Error msg # Line 18
> >     puts $h[:y]
> > end
> > show_y
> > show_y
>
> And if you really need something like this (hopefully you don't) try:
>
> $h = Hash.new {|the_hash, a_key| the_hash[a_key] = 0}
> def show_y
>   $h[:y] += 1
>   puts $h[:y]
> end
>
> and combining them:
>
> require 'singleton'
> class Counters
>   include Singleton
>   def initialize
>     @counts = Hash.new {|h, k| h[k] = 0}
>   end
>   def get_count(sym)
>     @counts[sym] += 1
>   end
> end
>
> c = Counter.instance
> c.get_count :y # => 1
> c.get_count :y # => 2
> c.get_count :z # => 1

Thanks for introducing me to the Singleton class from the Ruby
library.  I'm going to test whether that'll be work best for my
current project.

Best wishes,
Richard