Symbols in const assertions should be considered unique

[loilo]

TypeScript Version: 3.8.0-dev.20191205

Search Terms:

• const assertion unique symbol
• "unique symbol" "as const"

Code

const prop = Symbol()
const dictionary = {
  prop: Symbol()
}
const sealedDictionary = {
  prop: Symbol()
} as const

class MyClass {
  // Works because "prop" is a unique symbol
  [prop]: 1

  // Does not work because "dictionary.prop" is not a unique symbol
  [dictionary.prop]: 2

  // Does not work because "sealedDictionary.prop" is not a unique symbol,
  // even though it probably should be?
  [sealedDictionary.prop]: 3
}

Expected behavior:

MyClass should probably accept sealedDictionary.prop as a computed property name since it should be considered a unique symbol.

Actual behavior:

TypeScript complains with TS1166:

A computed property name in a class property declaration must refer to an expression whose type is a literal type or a 'unique symbol' type.

Playground Link: Provided Updated (old link seems to be broken in new playground)

Related Issues: —

[LANGERGabrielle]

It seems that symbols lose their "unique" when assigned to an object.

Another example of this behaviour: Playground.

[kyeotic]

@RyanCavanaugh you marked this as "awaiting more feedback". Can you elaborate on what that means? Is it community feedback or maintainer feedback you are looking for?

I ran into this problem the other and was convinced for a while that it was an issue with typescripts symbol index support, until I was pointed here. It would be really nice if this was fixed.

[jamesopstad]

Is the current behaviour intentional or an oversight? It's frustrating that to create an object of unique symbols you have to do this:

const a = Symbol();
const b = Symbol();
const symbols = { a, b } as const;

It would be nicer if you could declare the symbols directly:

const symbols = {
  a: Symbol(),
  b: Symbol()
} as const;

[omerd-cyera]

Any updates?
I ran into the same weird behaviour. Also, for my case i dont want the type to have readonly, so im looking for another way of creating the object.

[NWYLZW]

It is very inconvenient to write such code now. I have to do this:

const fooSymbols = {
  a: Symbol(),
  b: Symbol()
} as {
  readonly a: unique symbol
  readonly b: unique symbol
}

But there are indeed some things to consider about this issue, such as [[Getter]]:

const _b = Symbol()
const fooSymbols = {
  get a() {
    return Symbol()
  },
  get b() {
    return _b
  }
} as const

Is it possible to not process the properties corresponding to [[Getter]] but to process the properties of expression?
Processing refers to converting the corresponding symbol into unique symbol by as const.