Using TypeScript: Incorporating a map function in type declarations

Question

Using TypeScript: Incorporating a map function in type declarations

My current situation involves the following types:

type Value = boolean | number | string

class Struct<T extends Value[] = Value[]> {

    constructor(fmt: string) { }

    pack(...args: T): Buffer { }

}

I am seeking guidance on how to replace <???> with a list of the Value[] used by each Struct passed to the constructor in the snippet below:

class StructConcat<T extends Struct[]> {

    constructor(...structs: T) { }

    pack(...args_list: <???>) { }

}

// example:
const a: HeadStruct = new Struct<[number]>('<I')
const b: VectorStruct = new Struct<[number, number, number]>('<3f')
const concat = new StructConcat(a, b)

Ultimately, I want the StructConcat.pack function to be limited to this form:

concat.pack([1], [2, 3, 4])

So far, the closest solution I have found is:

(T[number] extends Struct<infer K> ? K : never)[]

but it still outputs

([number] | [number, number, number])[]

instead of

[[number], [number, number, number]]

as desired.

Is it possible within TypeScript's typing system to achieve this?

typescript typing

Answer 1

Answer №1

In the TypeScript version 3.1 and above, you now have the ability to utilize tuples within mapped types:

type Value = boolean | number | string

class Struct<T extends Value[] = Value[]> {

    constructor(fmt: string) { }

    pack(...args: T): Buffer { }

}

type ExtractValueFromStruct<T> = T extends Struct<infer V> ? V : never
type MapStructTuple<T extends Struct[]> = { 
    [P in keyof T]: ExtractValueFromStruct<T[P]>
}

class StructConcat<T extends Struct[]> {

    constructor(...structs: T) { }

    pack(...args_list: MapStructTuple<T>) { }

}

// For instance:
const a= new Struct<[number]>('<I')
const b= new Struct<[number, number, number]>('<3f')
const concat = new StructConcat(a, b)
concat.pack([1], [1, 2, 3])
concat.pack([1], [1, 2, 3, 4]) // This will result in an error

Answer 2

In the TypeScript version 3.1 and above, you now have the ability to utilize tuples within mapped types:

type Value = boolean | number | string

class Struct<T extends Value[] = Value[]> {

    constructor(fmt: string) { }

    pack(...args: T): Buffer { }

}

type ExtractValueFromStruct<T> = T extends Struct<infer V> ? V : never
type MapStructTuple<T extends Struct[]> = { 
    [P in keyof T]: ExtractValueFromStruct<T[P]>
}

class StructConcat<T extends Struct[]> {

    constructor(...structs: T) { }

    pack(...args_list: MapStructTuple<T>) { }

}

// For instance:
const a= new Struct<[number]>('<I')
const b= new Struct<[number, number, number]>('<3f')
const concat = new StructConcat(a, b)
concat.pack([1], [1, 2, 3])
concat.pack([1], [1, 2, 3, 4]) // This will result in an error

Using TypeScript: Incorporating a map function in type declarations

Answer №1

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