Type Alias UnwrapOpaque<OpaqueType>

UnwrapOpaque: OpaqueType extends Opaque<infer Type, OpaqueType[typeof tag]>
    ? Type
    : OpaqueType

Revert an opaque type back to its original type by removing the readonly [tag].

Why is this necessary?

  1. Use an Opaque type as object keys
  2. Prevent TS4058 error: "Return type of exported function has or is using name X from external module Y but cannot be named"

Type Parameters

  • OpaqueType extends Tagged<unknown>

Example

import type {Opaque, UnwrapOpaque} from 'type-fest';

type AccountType = Opaque<'SAVINGS' | 'CHECKING', 'AccountType'>;

const moneyByAccountType: Record<UnwrapOpaque<AccountType>, number> = {
	SAVINGS: 99,
	CHECKING: 0.1
};

// Without UnwrapOpaque, the following expression would throw a type error.
const money = moneyByAccountType.SAVINGS; // TS error: Property 'SAVINGS' does not exist

// Attempting to pass an non-Opaque type to UnwrapOpaque will raise a type error.
type WontWork = UnwrapOpaque<string>;

Settings

Member Visibility