No. 224 · Hard · template literal types

Join

Implement `Join<T, D>` so it concatenates a tuple of strings with the delimiter `D` between them. No delimiter before the first element or after the last.

Puzzle

join-tuple.ts

type Join<T extends readonly string[], D extends string> = ???

type Join<T extends readonly string[], D extends string> = ???

Stroke 1 of 4Not run yet

Replace ??? — your solution is checked against the cases below.

Checks

Join<['a', 'b', 'c'], '-'>—
→ 'a-b-c'
Join<['solo'], '-'>—
→ 'solo'
Join<[], '-'>—
→ ''
Join<['x', 'y'], ''>—
→ 'xy'

How a check is judged Exact type equality, not assignability — an intersection is not the same as the flattened object.

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