type T1 = ['a','b','c']
type T2 = ['d','e','f']
type TN = [.., .., ..]
type M = Concat<T1,T2,...,TN> //or Concat<[T1,T2,...,TN]>
//get ['a','b','c','d','e','f',...]
type Error =[...T1,...T2,...T3,...]//A rest element must be last in a tuple type.
I want concat many tuple types into one tuple. How to define type Concat<>?
With recursive conditional types (TS 4.1.0), you'll be able to:
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]
You can just use variadic tuple types (TS 4.0) instead of adding an additional type abstraction:
type T3 = ["g", "h", "i"]
type Concatenated = [...T1, ...T2, ...T3] // ["a", "b", ..., "h", "i"]
If there is still need for a separate Concat type, following will make use of TS 4.1 recursive conditional types and is more strict than Aleksey's answer:
// 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
For example you can combine this type with Array.prototype.concat:
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]
