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  • Constructors that produce frozen instances?

Constructors that produce frozen instances?

# Axel Rauschmayer (12 years ago)

It’s difficult to do that if you want your constructors to remain subtypable. Is the following the best we can do? A constructor can only freeze if it is the first constructor that is invoked.

function Point(x, y) {
    this.x = x;
    this.y = y;
    if (this.constructor === Point) {
        Object.freeze(this);
    }
}
function ColorPoint(x, y, color) {
    Point.call(this, x, y);
    this.color = color;
    if (this.constructor === ColorPoint) {
        Object.freeze(this);
    }
}
ColorPoint.prototype = Object.create(Point);
ColorPoint.prototype.constructor = ColorPoint;

(More detailed write-up: www.2ality.com/2013/06/freezing-instances.html )

# David Bruant (12 years ago)

Le 08/06/2013 20:22, Axel Rauschmayer a écrit :

It's difficult to do that if you want your constructors to remain subtypable. Is the following the best we can do? A constructor can only freeze if it is the first constructor that is invoked.

 function Point(x, y) {
     this.x = x;
     this.y = y;
     if (this.constructor === Point) {
         Object.freeze(this);
     }
 }
 function ColorPoint(x, y, color) {
     Point.call(this, x, y);

Super-ugly solution: warp 'this' in a proxy with a shadow (freezable) target and forward all non-freezing operations to 'this'.

     this.color = color;
     if (this.constructor === ColorPoint) {
         Object.freeze(this);
     }
 }
 ColorPoint.prototype = Object.create(Point);
 ColorPoint.prototype.constructor = ColorPoint;

(More detailed write-up: www.2ality.com/2013/06/freezing-instances.html )

Maybe classes and the @@construct separation (and convention) can help?