Re: [Rails-spinoffs] using Singleton with Prototype

[Andrew Tetlaw]

I had written a non-prototype several years ago like this:

var _singletons = []; // for storing singleton instances of objects

Function.prototype.singleton = function (o) {
        if(!_singletons[this.name]) {
                _singletons[this.name] = o;
                return false;
        }
        return true;
}

Function.prototype.getSingleton = function () {
  return _singletons[this.name];
}

then you define a class like this:

function AClass() {
 if AClass.singleton(this) return AClass.getSingleton();

 this.a = a;
 /* etc */
}

That way you can call var a = new AClass() as many times as you like
and it'd return the same object instance every time. Which I think is
close to a real singleton instance of an object.

But I don't think you could do that readily with Prototype using the
Class.create() mechanism.



On 22/05/06, Nicolas Terray <[EMAIL PROTECTED]> wrote:

On 5/22/06, Grzesiek Slusarek <[EMAIL PROTECTED]> wrote:
> Hello all. I'm writing my own object using prototype and I
> wonder how you write and call only one instance of class. Can
> anyone share his idea of singleton?
> thanks
> Gregor
>

Here is my proposal :
---8<----------------------
        <script>
        var Foo = Class.create();
        Object.extend(Foo.prototype, {
                initialize: function() {
                    this.a = 5;
                }
        });
        Object.extend(Foo, {
                instance: function() {
                    if (!this._instance) {
                        this._instance = new Foo();
                    }
                    return this._instance;
                }
        });
        var o1 = Foo.instance();
        var o2 = Foo.instance();
        alert(o1.a + ' ' + o2.a);
        o2.a = 10;
        alert(o1.a + ' ' + o2.a);

        </script>
---8<----------------------

Anyway it is not a real singleton since it is possible to call the
constructor outside from instance()
Furthermore, by hacking Foo, I do not know if I break something by
adding _instance and instance() :-\

Yours,
Nicolas Terray
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--
Andrew Tetlaw
htp://tetlaw.id.au

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