Enum lookup for map type [P in Enum] gives "implicit any index" error

[aaronbeall]

TypeScript Version: 2.5.3

It could be I stumbled on something I simply don't understand, but it seems like this should work:

Code

enum Color {
  RED = "RED",
  BLUE = "BLUE",
  GREEN = "GREEN"
}

type ColorMap = {
  [P in Color]: number; // type ColorMap = { RED: number; BLUE: number; GREEN: number; }
}

declare const color: Color;
map[color] // Error: Element implicitly has an 'any' type because type 'ColorMap' has no index signature.

All of the following work:

declare const map: ColorMap;
map[Color.RED] // OK

const red: Color = Color.RED;
map[red] // OK

declare const color: keyof typeof Color;
map[color] // OK -- I don't know why this works

Expected behavior:

map[color] to work and give return type of number

Actual behavior:

map[color] // Error: Element implicitly has an 'any' type because type 'ColorMap' has no index

[aaronbeall]

More stuff I don't understand:

declare const color: Color.RED | Color.BLUE | Color.GREEN;
map[color] // Error: Element implicitly has an 'any' type because type 'ColorMap' has no index signature.

declare const color: Color.RED | Color.BLUE | "GREEN";
map[color] // OK

[aaronbeall]

I think my confusion lies with how the compiler actually "sees" the enum type... I thought that string enum was equivalent to the old string literal type + namespace workaround:

type Color = "RED" | "BLUE" | "GREEN"
namespace Color { export const RED = "RED"; export const BLUE = "BLUE"; export const GREEN = "GREEN"; }

type ColorMap = {
  [P in Color]: number;
}

declare const map: ColorMap;
map[Color.RED] // OK

const red: Color = Color.RED;
map[red] // OK

declare const color: Color;
map[color] // Ok

But it obviously is a different thing that isn't as intuitive to me...

[aluanhaddad]

I've also found this very counterintuitive. The workaround was more verbose but was expressive and allowed for very convenient consumption.

[mhegazy]

Duplicate of #16760. Should be fixed by #18029

[typescript-bot]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.