Runtime type checking

[jednano]

I request a runtime type checking system that perhaps looks something like this:

function square(x: number!) {
  return x * x;
}

Where the ! tells the compiler to generate a runtime type check for a number, something akin to tcomb.js.

Of course, this gets much more complicated with interfaces, but you get the idea.

[basarat]

Perhaps something more akin to google AtScript for consistency. Basically flag --rtts will cause emited JS to have rtts (runtime type system) checks inserted.

[jednano]

I'm suggesting, however, that you can optionally enable runtime type checking on some args and not others. Or, at least, skip type checking on private methods, optionally.

[RyanCavanaugh]

This remains outside our design goals (https://github.com/Microsoft/TypeScript/wiki/TypeScript-Design-Goals)

[davidrapin]

For people like me coming here looking with high hopes, you might want to take a look at http://angular.github.io/assert/

[jeansson]

Well, this can't be very complex to implement since you already have the infrastructure for type checking. At least you could expect to get injected type checking for primitive types when compiling with --debug, as mentioned in the other thread:

This has lead us to introduce type checks for all exported functions in TypeScript, although they really feel verbose in a typed language.

export function add(x: number, y: number): number {
  if (typeof x !== 'number' || typeof y !== 'number') {
    throw new TypeError('x and y need to be numbers');
  }
  return x + y;
}

If this does not match your design goals, maybe you should change them?

[aluanhaddad]

Primitive TypeChecking is easy, and the results of doing it yourself guide type inference. If you expect to receive something other than the indicated type, perhaps you should not specify number.