Question:

How to map an array of types to another array of types in TypeScript?

Problem

I want to make a class to wrap some primitive types into another such as:

class MyClass<T> {

foo? : T

}

type Input = [string, number, boolean]

type Remap<T> = MyClass<T>

type Output = Remap<Input> // <-- Now it's MyClass<Input>

// Can I make the Remap to infer an Output as the following?

// type Output = [MyClass<string>, MyClass<number>, MyClass<boolean>]

But I don't know how to, if doable, make a proper Remap type to make the Output match my expectation.

Solution

Yes, in fact, this can be done with a plain >mapped type:

type Remap<T> = { [I in keyof T]: MyClass<T[I]> }

type Output = Remap<Input>

// ^? type Output = [MyClass<string>, MyClass<number>, MyClass<boolean>]

Mapped types that act on keyof T where T is a generic type parameter automatically >transform arrays to arrays and tuples to tuples.

Nisha Patel

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