ts-data-forge/src/functional/optional/impl/optional-is-optional.mts

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import { isRecord } from '../../../guard/index.mjs';
import { NoneTypeTagName, SomeTypeTagName } from './tag.mjs';

/**
 * Checks if the given value is an {@link Optional}.
 *
 * @example
 *
 * ```ts
 * const maybeOptional = Optional.some('value');
 *
 * const notOptional = { $$tag: 'ts-data-forge::Optional.some' };
 *
 * assert.isTrue(Optional.isOptional(maybeOptional));
 *
 * assert.isFalse(Optional.isOptional(notOptional));
 * ```
 *
 * @param maybeOptional The value to check.
 * @returns `true` if the value is an {@link Optional}, otherwise `false`.
 */
export const isOptional = (
  maybeOptional: unknown,
): maybeOptional is Optional<unknown> =>
  isRecord(maybeOptional) &&
  Object.hasOwn(maybeOptional, '$$tag') &&
  ((maybeOptional['$$tag'] === SomeTypeTagName &&
    Object.hasOwn(maybeOptional, 'value')) ||
    maybeOptional['$$tag'] === NoneTypeTagName);