Flexibility of template literal types for enums

Search Terms

template literal type enum permutations

Suggestion

Typescript 4.1 brought template literal types, which make it simple to express all the possibilities of permutations of unions of string types concatenated together. It would be cool if there was some equivalent syntax for expressing enum key/value pairs with the same level of expressivity that template literal types provide.

Use Cases

However, my codebase right now uses enums for these kinds of string types, so if I want to express a bunch of permutations of possible values with an enum, I can't really leverage template literal types in this case.

Examples

this is just some syntax I'm making up, I don't know how this would work especially for dealing with keys and values separately:

enum Color {
  RED,
  BLUE
}
enum Shape {
  SQUARE,
  CIRCLE
}
enum ColoredShape {
  [`${keyof Color}_${keyof Shape}`]
}

console.log(ColoredShape.RED_SQUARE, ColoredShape.BLUE_CIRCLE)

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.
  • I think?

Start by reviewing the issue's proposed interaction between template literal types and enum key/value pairs. The payload names no files, tests, or entry points, and the syntax and semantics remain speculative. Done would require a settled design for enum permutations and a clear implementation and validation plan.