Typescript: proposal:symbol enum

[kgtkr]

I want symbol enum.

syntax example:

symbol enum Example{
  X,Y,Z
}

↓

var Example;
(function (Example) {
    Example[Example["X"] = new Symbol("X")] = "X";
    Example[Example["Y"] = new Symbol("Y")] = "Y";
    Example[Example["Z"] = new Symbol("Z")] = "Z";
})(Example || (Example = {}));

[mhegazy]

We first need a way to treat symbols as literals, just like string and numeric literals. this is covered in https://github.com/Microsoft/TypeScript/pull/15473

[nisimjoseph]

I see #15473 merged, does it mean we can use Symbols in Enum somehow?
I want to use Enum with the Types: string, number or Symbol.

[fbartho]

Not to bikeshed, but wouldn't a more consistent syntax be:

enum Example: Symbol {
  X,Y,Z
}
// or
enum Example<Symbol> {
  X,Y,Z
}

Rather than introducing a new keyword of symbol these options either use inheritance style, or Generics, and would pave the way for arbitrary-valued enums?

[DanielRamosAcosta]

This would be very useful with Redux actions...

[Larry1123]

Is there something that would help move this issue?
If it would just be making a PR at this point I might be able to do it, may need to be guided in the right direction to start.

[littleclown]

I've found an alternative way to do it, and I hope it helps:

/**
 * Action types for StoreState.todo
 */
export namespace TodoActionTypes {
  // Adding todo item
  export const ADD_ITEM = Symbol('@todo/ADD_ITEM')
  export type ADD_ITEM = typeof ADD_ITEM

  // Removing todo item
  export const DEL_ITEM = Symbol('@todo/DEL_ITEM')
  export type DEL_ITEM = typeof DEL_ITEM

  // Performing undo on StoreState.todo
  export const UNDO = Symbol('@todo/UNDO')
  export type UNDO = typeof UNDO

  // Performing redo on StoreState.todo
  export const REDO = Symbol('@todo/REDO')
  export type REDO = typeof REDO
}


/**
 * Action types for StoreState.todo
 */
export type TodoActionTypes =
  | TodoActionTypes.ADD_ITEM
  | TodoActionTypes.DEL_ITEM
  | TodoActionTypes.UNDO
  | TodoActionTypes.REDO

[cosmoarunn]

I've found an alternative way to do it, and I hope it helps:

/**
 * Action types for StoreState.todo
 */
export namespace TodoActionTypes {
  // Adding todo item
  export const ADD_ITEM = Symbol('@todo/ADD_ITEM')
  export type ADD_ITEM = typeof ADD_ITEM

  // Removing todo item
  export const DEL_ITEM = Symbol('@todo/DEL_ITEM')
  export type DEL_ITEM = typeof DEL_ITEM

  // Performing undo on StoreState.todo
  export const UNDO = Symbol('@todo/UNDO')
  export type UNDO = typeof UNDO

  // Performing redo on StoreState.todo
  export const REDO = Symbol('@todo/REDO')
  export type REDO = typeof REDO
}


/**
 * Action types for StoreState.todo
 */
export type TodoActionTypes =
  | TodoActionTypes.ADD_ITEM
  | TodoActionTypes.DEL_ITEM
  | TodoActionTypes.UNDO
  | TodoActionTypes.REDO

i guess this will do?

export type TodoActionTypes =
  | ADD_ITEM
  | DEL_ITEM
  | UNDO
  | REDO

[polomsky]

I have found another solution at https://fettblog.eu/symbols-in-javascript-and-typescript/ and I slightly improved it. Sadly, there is lot of code around it, but it gives pretty protection (compile time and runtime)

const COLOR_RED = Symbol('COLOR_RED');
const COLOR_ORANGE = Symbol('COLOR_ORANGE');

// intentionally not part of the enum for demonstration
const COLOR_GREEN = Symbol('COLOR_GREEN');

// freeze needed for runtime protection
export const colors = Object.freeze({
    COLOR_RED,
    COLOR_ORANGE,
} as const);

type ValuesWithKeys<T, K extends keyof T> = T[K];
type Values<T> = ValuesWithKeys<T, keyof T>

export type COLOR = Values<typeof colors>;

function foo(val: COLOR) {

}

foo(COLOR_RED);
foo(colors.COLOR_ORANGE);
foo(COLOR_GREEN); // refused by typescript