Method optionalKey

repos/effect/packages/effect/src/Optic.ts:617–617

* Focuses on a key where setting `undefined` **removes** the key from the * struct (or splices the element from an array/tuple). * * **Details** * * - The focus type becomes `A[Key] | undefined`. * - Does **not** work on union types (compile error). * * **Example** (Deleting

(
    this: Lens<S, A>,
    key: Key,
    ..._err: ForbidUnion<A, "cannot use `optionalKey` on a union type">
  )

   *   { expected: `"b" tag` }
   * )
   *
   * _b.getResult({ _tag: "b", b: 1 }) // => Result.succeed({ _tag: "b", b: 1 })
   * ```
   *