How to convert a string literal type to the keys of a new type?

Issue

Let's suppose I have a string literal type:

type Letters = "a" | "b" | "c" | "d" | "e";

How can I create the following type based on Letters?

type LetterFlags = {a: boolean, b: boolean, c: boolean, d: boolean, e: boolean};

---

I have tried

type Flags<T> = { [k in keyof T]: boolean };
type LetterFlags = Flags<Letters>;

but

const flags: LetterFlags = {a: true, b: false, c: true, d: false, e: true};

raises

Type '{ a: boolean; b: boolean; c: boolean; d: boolean; e: boolean; }' is not assignable to type '"e"'.

Solution

You could do like this:

type Letters = "a" | "b" | "c" | "d" | "e";

type Flags<T extends PropertyKey> = Record<T, boolean>;
type LetterFlags = Flags<Letters>;

const flags: LetterFlags = { a: true, b: false, c: true, d: false, e: true };

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Answered By - Guerric P