Subtract

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题目

Implement the type Subtraction that is - in Javascript by using BuildTuple.

If the minuend is less than the subtrahend, it should be never.

It's a simple version.

For example

Subtract<2, 1>; // expect to be 1
Subtract<1, 2>; // expect to be never

解答

type ConstructTuple<
  L extends number,
  R extends unknown[] = []
> = R["length"] extends L ? R : ConstructTuple<L, [...R, unknown]>;

// M => minuend, S => subtrahend
type Subtract<M extends number, S extends number> = ConstructTuple<M> extends [
  ...subtrahend: ConstructTuple<S>,
  ...rest: infer Rest
]
  ? Rest["length"]
  : never;