type A1 = ['x','y','z']
type A2 = ['u','v','w']
type AN = [.., .., ..]
type C = Combine<A1,A2,...,AN> //or Combine<[A1,A2,...,AN]>
//resulting in ['x','y','z','u','v','w',...]
type Issue =[...A1,...A2,...A3,...]//An additional element should be placed at the end of a tuple type.
I am looking to merge multiple tuple types together into one common tuple. How can I define the type Combine<>?
Introducing recursive conditional types in TypeScript version 4.1.0 allows for:
type T1 = ['a', 'b', 'c']
type T2 = ['d', 'e', 'f']
type TN = [1, 2, 3]
type Concat<T> = T extends [infer A, ...infer Rest]
? A extends any[] ? [...A, ...Concat<Rest>] : A
: T;
type C = Concat<[T1, T2, TN]>; // ["a", "b", "c", "d", "e", "f", 1, 2, 3]
To simplify the code, you can utilize variadic tuple types in TypeScript 4.0 instead of creating an additional type abstraction:
type T3 = ["g", "h", "i"]
type Concatenated = [...T1, ...T2, ...T3] // ["a", "b", ..., "h", "i"]
If you still require a separate Concat type, you can make use of recursive conditional types in TypeScript 4.1, which is stricter than Aleksey's solution:
// separate initial and recursive type constructor
type Concat<T extends unknown[][]> = ConcatRec<T>
type ConcatRec<T extends unknown[]> = T extends [infer I, ...infer R] ?
I extends unknown[] ? [...I, ...ConcatRec<R>] : never
: T
type R1 = Concat<[T1, T2, T3]>; // ["a", "b", "c", ... , "i"]
type R2 = Concat<["foo"]>; // now errors properly
You can combine this type with Array.prototype.concat as shown below:
function concat<T extends [unknown, ...unknown[]][]>(...t: T): Concat<T> {
return [].concat(...t as any) as any
}
const result = concat([1, "a", 3], [true, 5, new Date()])
// const res: [number, string, number, boolean, number, Date]
Check out the Live code sample on Playground
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