Method modify

repos/effect/packages/effect/src/Optic.ts:559–559

* Returns a function `(s: S) => S` that applies `f` to the focused value. * If the optic cannot focus, the original `s` is returned unchanged. * * **Example** (Incrementing a nested field) * * ```ts * import { Optic } from "effect" * * type S = { readonly a: { readonly b: num

(f: (a: A) => A)

    this: Lens<S, A>,
    key: Key,
    ..._err: ForbidUnion<A, "cannot use `optionalKey` on a union type">
  ): Lens<S, A[Key] | undefined>
  optionalKey<S, A extends object, Key extends keyof A>(
    this: Optional<S, A>,