@std/collections `zip` with customizable handling of where to truncate (longest vs shortest)

[lionel-rowe]

Is your feature request related to a problem? Please describe.

Sometimes it's useful to zip arrays together without truncating the shorter ones, instead filling with undefined.

Describe the solution you'd like

Allow passing an option such as options.truncate = 'longest' to continue zipping until the longest array ends, filling missing values with undefined.

Describe alternatives you've considered

Not really sure how best to add this to the current function signature, given the variadic ...arrays param.

One possible option would be taking options as an initial parameter, which could be detected at runtime with Array.isArray:

type ZipOptions = {
  truncate?: 'shortest' | 'longest';
}

export function zip<T extends unknown[], O extends ZipOptions>(
  options: O,
  ...arrays: { [K in keyof T]: ReadonlyArray<T[K]> }
): {
  [K in keyof T]: O extends { truncate: "longest" } ? T[K] | undefined : T[K];
}[];
export function zip<T extends unknown[]>(
  ...arrays: { [K in keyof T]: ReadonlyArray<T[K]> }
): T[];
export function zip(
  ...args: unknown[]
): unknown[] {
  const [options, arrays] = args.length === 0 || Array.isArray(args[0]) ?
    [{}, args as unknown[][]] :
    [args[0] as ZipOptions, args.slice(1) as unknown[][]];

Otherwise, it might need to be a separate zipWithOptions function.

[lionel-rowe]

Joint iteration proposal calls it "mode" with options "shortest" | "longest" | "strict", and additionally a padding option for longest mode.