Never

If you need a codec that is never valid, you can use ft.Never. You might use this as the type for an API endpoint that's not yet implemented and so you don't want it to ever be called.

import * as ft from "funtypes";

const MyCodec = ft.Never;
// => ft.Codec<never>
type MyType = ft.Static<typeof MyCodec>;
// => never

// 🚨 Never will always throw when you try to
//    parse something
assert.throws(() => MyCodec.parse({}));

If you use ft.Never inside a Union, it's effectively removed from the list of possibilities.

import * as ft from "funtypes";

const MyUnion = ft.Union(ft.String, ft.Never);
// => ft.Codec<string>

type MyType = ft.Static<typeof MyCodec>;
// => string

// ✅ Can parse the other types in the union
assert.deepEqual(
  MyCodec.parse("Hello World"),
  "Hello World",
);