Tuple

Use ft.Tuple to validate an unknown value is a tuple, i.e. an array of a specific length with specific types for each value in the array.

Simple Tuple

import * as ft from "funtypes";

export const MyTupleCodec = ft.Tuple(
  ft.Number,
  ft.String,
);
// => ft.Codec<[number, string]>
export type MyTuple = ft.Static<
  typeof MyTupleCodec
>;
// => [number, string]

// ✅ Valid tuple
assert.deepEqual(MyTupleCodec.parse([42, "42"]), [
  42,
  "42",
]);

// 🚨 Tuple is too short
assert.throws(() => MyTupleCodec.parse([42]));

// 🚨 Tuple is too long
assert.throws(() =>
  MyTupleCodec.parse([42, "42", "Forty Two"]),
);

// 🚨 Tuple has the wrong types
assert.throws(() =>
  MyTupleCodec.parse(["42", 42]),
);

// 🚨 Not an array
assert.throws(() =>
  MyTupleCodec.parse({ 0: 42, 1: "42" }),
);

ReadonlyTuple

The ft.ReadonlyTuple type has the same runtime behaviour as ft.Tuple, but the type is a readonly array, rather than a mutable array.

import * as ft from "funtypes";

export const MyTupleCodec = ft.ReadonlyTuple(
  ft.Number,
  ft.String,
);
// => ft.Codec<readonly [number, string]>
export type MyTuple = ft.Static<
  typeof MyTupleCodec
>;
// => readonly [number, string]

// ✅ Valid tuple
assert.deepEqual(MyTupleCodec.parse([42, "42"]), [
  42,
  "42",
]);

// 🚨 Tuple is too short
assert.throws(() => MyTupleCodec.parse([42]));

// 🚨 Tuple is too long
assert.throws(() =>
  MyTupleCodec.parse([42, "42", "Forty Two"]),
);

// 🚨 Tuple has the wrong types
assert.throws(() =>
  MyTupleCodec.parse(["42", 42]),
);

// 🚨 Not an array
assert.throws(() =>
  MyTupleCodec.parse({ 0: 42, 1: "42" }),
);