From: Leo <minilith@...>
Date: 2009-03-08T18:29:11+09:00
Subject: Re: Can I access or find a object from it's instance variable?

> class Foo
>   attr_reader :key
>
>   @@instances = Hash.new {|h,k| h[k] = []}
> [...]
>   def initialize(key_val)
>     @key = key_val
>     @@instances[key_val] << self
>   end
> end

I don't know ruby well enough but I'd assume a weak reference would be
preferable -- unless the script won't run very long anyway.

In general, if you want control over the instances of a class, you
could also consider something singleton like:


require 'weakref'

class Foo
    attr_reader :key
    @instances = {}

    def initialize(key)
        @key = key
    end

    def self.instance(key)
        find(key) || Foo.new(key).tap {|o| @instances[key] =
WeakRef.new(o)}
    end

    def self.find(key)
        if @instances.has_key?(key) and @instances[key].weakref_alive?
            @instances[key].__getobj__
        end
    end
end

a = Foo.instance("a")
a1 = Foo.instance("a")
a2 = Foo.find("a")
p a.object_id, a1.object_id, a2.object_id