Subj : Re: defining operators for custom classes (SpiderMonkey)
To   : netscape.public.mozilla.jseng
From : zwetan
Date : Tue Oct 12 2004 04:11 pm

> Is it possible to do 'operator overloading' for custom classes in
> SpiderMonkey?
>
> I.E.:
> --------------------------------
> var objA = new MyObject();   // custom class backed by native source
> var objB = new MyObject();
>
> var objC = objA + objB;        // call some native source function to
> calcualte the result
> ---------------------------------
>
> Looks alot better than
>
> var objC = objA.Plus(objB);
>

nope, but you can fake it in certain ways overloading the valueOf method
and returning a primitive

(sorry if the answer sound off topic, meaning not related to js engine)


MyObject.prototype.valueOf = function()
    {
    return this._value; /*Number*/
    }

and then you could something as

var objC = new MyObject( objA + objB );

provided that your constructor accept the primitive type as argument

MyObject= function( /*Number*/ value  )
    {
    this._value = value;
    }


concrete exemple: a Version constructor

instead of doing that:
Version = function( /*Int*/ major, /*Int*/ minor, /*Int*/ build, /*Int*/
revision )
    {
    this.major = major;
    this.minor = minor;
    this.build = build;
    this.revision = revision;
    }

you re doing this:
Version = function( /*Int*/ major, /*Int*/ minor, /*Int*/ build, /*Int*/
revision )
    {
    this._value = major << 24 | minor << 20 | build << 8 | revision;
    }

then:
Version.prototype.valueOf = function()
    {
    return this._value;
    }

this allow you to use operator directly on the custom object:

test1 = new Version(1,0,0,0);
test2 = new Version(1,0,2,0);

if( test1 < test2 )
    {
    //code here
    }

and if you want to add two or more Version object modify the constructor:

Version = function( /*Int*/ major, /*Int*/ minor, /*Int*/ build, /*Int*/
revision )
    {
    if( arguments.length == 1 )
        {
        this._value = arguments[0];
        }
    else
        {
        this._value = major << 24 | minor << 20 | build << 8 | revision;
        }
    }

test3 = new Version( test1 + test2 ); // v2.0.2.0

HTH
zwetan

note: this is just simple exemple not solid code ;)

.