rivo/Ary/IsTuple.d.ts

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import type { Ary } from ".";
import type { Args, Fn } from "../HKT";
import type IsNatFn from "../Num/Nat/IsNat";
import type { Filter } from "../Union/Filter";
import type { If, IsAny, IsNever, Not } from "../helpers";

/**
 * Check if an {@link Ary} (i.e., `Array` or `ReadonlyArray`) is a tuple.
 *
 * Sig: `(a: Ary) => boolean`
 *
 * @example
 * ```typescript
 * type R1 = IsTuple<string[]>;
 * //   ^?: false
 * type R2 = IsTuple<readonly number[]>;
 * //   ^?: false
 * type R3 = IsTuple<["foo", "bar"]>;
 * //   ^?: true
 * type R4 = IsTuple<readonly [42, 1337, ...string[]]>;
 * //   ^?: true
 * type R6 = IsTuple<readonly [...string[]]>;
 * //   ^?: false, because `readonly [...string[]]` is actually equal to `readonly string[]`, and
 * //              the same is true for something like `[...(number | string)[]]`, which is equal to
 * //              `(number | string)[]`, etc.
 * type R7 = IsTuple<[]>;
 * //   ^?: true
 * ```
 */
export type IsTuple<A extends Ary> = If<
  IsAny<A>,
  boolean,
  A extends A ?
    A["length"] extends 0 ?
      true
    : Not<IsNever<Filter<IsNatFn, Exclude<keyof A, keyof [] | keyof (readonly [])>>>>
  : never
>;

/**
 * [Fn] Check if an {@link Ary} (i.e., `Array` or `ReadonlyArray`) is a tuple.
 *
 * Sig: `(a: Ary) => boolean`
 */
export default interface IsTupleFn extends Fn<[Ary], boolean> {
  def: ([a]: Args<this>) => IsTuple<typeof a>;
}