Adjust the specific data type to match its relevant category

Is there a method to alter literal types in TypeScript, for instance.

type T1 = "";
type T2 = 1

I am interested in obtaining string for T1 and number for T2.

Regarding collections, I am unsure, but I assume it would involve applying it to the generic type, though that is not my main concern at the moment.

In my current scenario, I am extracting the type from a generic function with a const annotation.

const f = <const T>(x:T)=> ...

since I require the precise literal type but also a more general type (its supertype?)

At this point, the only solution I can think of involves creating a type that manually checks if the type extends it and then returns that corresponding type.

type Z<T>=T extends string ? string : T extends number ? number ...

This approach should suffice if no other alternatives are available.

Thank you for any assistance.

typescript

Answer №1

Unfortunately, there is no alternative method to obtain the primitive type for a given type.

A more comprehensive version of what you attempted can be found in the type-samurai package under the ToPrimitive type:

type ToPrimitive<T> = T extends string
  ? string
  : T extends number
  ? number
  : T extends null
  ? null
  : T extends undefined
  ? undefined
  : T extends boolean
  ? boolean
  : T extends bigint
  ? bigint
  : T extends symbol
  ? symbol
  : {
      [K in keyof T]: ToPrimitive<T[K]>;
    };

In addition to primitive types like numbers, strings, and so on, it also handles nested objects/arrays by converting their properties to primitives.

Test Cases:

// number
type Case1 = ToPrimitive<1>
// string
type Case2 = ToPrimitive<'str'>
// {a: string}
type Case3 = ToPrimitive<{a: '1'}>

playground

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