Literal

Use ft.Literal to validate an unknown value is exactly equal to a specific value. This is most useful in unions.

Union of literals

import * as ft from "funtypes";

export const ObjectKindCodec = ft.Union(
  ft.Literal("USER"),
  ft.Literal("POST"),
);
// => ft.Codec<"USER" | "POST">

export type ObjectKind = ft.Static<
  typeof ObjectKindCodec
>;
// => "USER" | "POST"

// ✅ Valid value
assert.deepEqual(
  ObjectKindCodec.parse("USER"),
  "USER",
);
assert.deepEqual(
  ObjectKindCodec.parse("POST"),
  "POST",
);

// 🚨 Invalid value
assert.throws(() => ObjectKindCodec.parse(42));

// 🚨 Invalid value
assert.throws(() =>
  ObjectKindCodec.parse("SOME_OTHER_STRING"),
);