Abstract Functions

[alongubkin]

The abstract modifier indicates that a function has a missing or incomplete implementation. Useful for inheritance.

abstract fn Animal() {
}

fn Snake() extends Animal() {
}

var snake = new Snake(); // ok
var animal = new Animal(); // error - Animal is abstract

[alongubkin]

Implementation:

function Animal() {
  if (!this.__extending) {
    throw "cannot create a new instance of Animal because it is abstract.";
  }
}

function Snake() {
  this.__extending = true;
  Animal.call(this);
}

Snake.prototype = Object.create(Animal);

var snake = new Snake(); // ok
var animal = new Animal(); // error - Animal is abstract

[zekesonxx]

This, while a good solution, is adding runtime code, which is bad.

I'm beginning to think that we need a compiler flag to specify if it's a production or development build, and only put these kinds of things in production.

Also, line 3 should be throw new Error("Cannot create a new instance of Animal because it is abstract.");

[Namek]

I would put runtime checks only in development build. Production has to be fast.

[Namek]

#89: Proposal: Split developer/production compilation modes