Is there a way to create nominal types in TypeScript that extend primitive types?

Issue

Say I have two types of numbers that I'm tracking like latitude and longitude. I would like to represent these variables with the basic number primitive, but disallow assignment of a longitude to a latitude variable in typescript.

Is there a way to sub-class the number primitive so that typescript detects this assignment as illegal? Someway to coerce nominal typing so that this code fails?

var longitude : LongitudeNumber = new LongitudeNumber();
var latitude : LatitudeNumber;
latitude = longitude; // <-- type failure

The answer to "How to extend a primitive type in typescript?" seems like it will put me in the right direction, but I am not sure how to extend that solution to create distinct nominal sub-types for different kinds of numbers.

Do I have to wrapper the primitive? If so, can I make it behave somewhat seamlessly like a normal number or would I have to reference a sub-member? Can I just somehow create a typescript compile-time number subclass?

Solution

There isn't a way to do this.

A suggestion tracking this on the GitHub site is Units of Measure.

In a future release, you'll be able to use type to define alternate names for the primitives, but these will not have any checking associated with them:

type lat = number;
type lon = number;
var x: lat = 43;
var y: lon = 48;
y = 'hello'; // error
x = y; // No error

Answered By - Ryan Cavanaugh