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cats-eo-api-docs/dev.constructive.eo/dev.constructive.eo.optics/Optional

Optional

dev.constructive.eo.optics.Optional
See theOptional companion object
sealed abstract class Optional[S, T, A, B] extends Optic[S, T, A, B, Affine], CanGetOption[S, A], CanModifyP[S, T, A, B], CanFold[S, A]

The conditionally-present single-focus optic over the Affine carrier. Every operation tears the source ONCE: getOrModify / getOption / foldMap read without building anything a write would need, modify / replace tear once and rebuild from what they tore, and the carrier pair to / from keeps what the read computed — the existential intermediate M — so a generic write through to / from never tears S a second time either.

Two implementations, both private: Optional.apply (hand-written getOrModify + reverseGet; M = S, the source is all the user's reverseGet needs) and the fused compositions (prism.andThen(lens), optional.andThen(optional), …), whose M is whatever the outer step already produced — a prism ∘ lens keeps the decoded domain value, so writing back re-uses it instead of decoding again, and a nested chain keeps a tuple of its levels' intermediates.

Fused .andThen overloads skip the generic AssociativeFunctor[Affine] round-trip whenever the other side is a known concrete class.

Attributes

Companion
object
Source
Optional.scala
Graph
Supertypes
trait CanFold[S, A]
trait CanModifyP[S, T, A, B]
trait CanGetOption[S, A]
trait Optic[S, T, A, B, Affine]
trait Serializable
class Object
trait Matchable
class Any
Show all

Members list

Grouped members

Operations

inline def cross[C, D](o: Optic[T, S, C, D, Affine])(using Accessor[Affine], ReverseAccessor[Affine]): Optic[B, A, C, D, Affine]

Build-then-observe across the build-output ⇄ read-input seam, preserving structure, on a shared carrier F. Flip self (it must be reversible — Accessor[F] and ReverseAccessor[F], i.e. an Iso or Review over Direct) so it reads T from B, then andThen that under the same carrier. The result is the full Optic[B, A, C, D, F], not a collapsed getter: its read capability follows the carrier (.get for Direct), and self's read focus A survives as the composite's write-back focus.

Build-then-observe across the build-output ⇄ read-input seam, preserving structure, on a shared carrier F. Flip self (it must be reversible — Accessor[F] and ReverseAccessor[F], i.e. an Iso or Review over Direct) so it reads T from B, then andThen that under the same carrier. The result is the full Optic[B, A, C, D, F], not a collapsed getter: its read capability follows the carrier (.get for Direct), and self's read focus A survives as the composite's write-back focus.

This is exactly self.reverse.andThen(that). The motivating case is ana.cross(cata): a Review (the unfold) crossed with a getter on the built S (the fold) — a (materializing) hylomorphism whose .get reads the folded value. When that sits on a different carrier (a Prism, a Fold, …), the cross-carrier cross overload below is selected instead.

Seam: that's source is self's T and its back-type is self's S.

Attributes

Inherited from:
Optic
Source
Optic.scala

Type members

Types

type M

What a hit keeps for the write: the part of the read the rebuild needs.

What a hit keeps for the write: the part of the read the rebuild needs.

Attributes

Source
Optional.scala
type X = (T, M)

Existential leftover carried alongside the focus — the type-level witness the carrier uses to rebuild T. Concrete at construction (Lens.apply sets X = S, Prism.apply sets X = S, …) and abstract when the optic is bound to Optic[…, F] without refinement.

Existential leftover carried alongside the focus — the type-level witness the carrier uses to rebuild T. Concrete at construction (Lens.apply sets X = S, Prism.apply sets X = S, …) and abstract when the optic is bound to Optic[…, F] without refinement.

Attributes

Source
Optional.scala

Value members

Abstract methods

def getOrModify(s: S): Either[T, A]

The read: Right(a) on a hit, Left(t) (the pass-through T) on a miss.

The read: Right(a) on a hit, Left(t) (the pass-through T) on a miss.

Attributes

Source
Optional.scala
def rebuild(m: M, b: B): T

Write b back from what a hit kept — never re-reads S.

Write b back from what a hit kept — never re-reads S.

Attributes

Source
Optional.scala
def to(s: S): Affine[X, A]

The carrier read: a hit keeps its intermediate m beside the focus, for rebuild.

The carrier read: a hit keeps its intermediate m beside the focus, for rebuild.

Attributes

Source
Optional.scala

Concrete methods

inline def andThen[C, D](inner: Optional[A, B, C, D]): Optional[S, T, C, D]

Fused Optional.andThen(Optional) — two partial focuses compose into another. An inner miss lifts the inner's leftover back through the outer's rebuild (the outer's own intermediate, not a re-read). inline so a deep optional.andThen(optional)… chain splices distinct lambdas per level, under C2's recursive-inline cap (see Getter.andThen).

Fused Optional.andThen(Optional) — two partial focuses compose into another. An inner miss lifts the inner's leftover back through the outer's rebuild (the outer's own intermediate, not a re-read). inline so a deep optional.andThen(optional)… chain splices distinct lambdas per level, under C2's recursive-inline cap (see Getter.andThen).

Attributes

Source
Optional.scala
def andThen[C, D](inner: GetReplaceLens[A, B, C, D]): Optional[S, T, C, D]

Fused Optional.andThen(Lens) — always-present inner inside a partial outer. Stays partial; the write keeps the outer's intermediate and the outer focus the lens writes into.

Fused Optional.andThen(Lens) — always-present inner inside a partial outer. Stays partial; the write keeps the outer's intermediate and the outer focus the lens writes into.

Attributes

Source
Optional.scala
def andThen[C, D](inner: MendTearPrism[A, B, C, D]): Optional[S, T, C, D]

Fused Optional.andThen(Prism) — outer Optional's hit fed into a Prism; an inner miss lifts the prism's leftover through the outer's rebuild.

Fused Optional.andThen(Prism) — outer Optional's hit fed into a Prism; an inner miss lifts the prism's leftover through the outer's rebuild.

Attributes

Source
Optional.scala
def andThen[C, D](inner: BijectionIso[A, B, C, D]): Optional[S, T, C, D]

Fused Optional.andThen(Iso) — iso is transparent; threads through the Optional's shape.

Fused Optional.andThen(Iso) — iso is transparent; threads through the Optional's shape.

Attributes

Source
Optional.scala
def foldMap[F](f: A => F)(s: S)(using F: Monoid[F]): F

Attributes

Source
Optional.scala
final def from(a: Affine[X, B]): T

Close the carrier: given a modified focus B (and the leftover X already inside the F), reassemble the result T.

Close the carrier: given a modified focus B (and the leftover X already inside the F), reassemble the result T.

Attributes

Source
Optional.scala
def getOption(s: S): Option[A]

Attributes

Source
Optional.scala
inline def modify(f: A => B): S => T

inline, like GetReplaceLens.modify: optional.modify(f)(s) reduces to modifyAt(s, f).

inline, like GetReplaceLens.modify: optional.modify(f)(s) reduces to modifyAt(s, f).

Attributes

Source
Optional.scala
def modifyAt(s: S, f: A => B): T

One tear, then rebuild: the write behind modify / replace, taking the source directly so a modify(f)(s) call site allocates no S => T closure (modify is inline). Fused compositions override it with a kernel that builds no carrier at all.

One tear, then rebuild: the write behind modify / replace, taking the source directly so a modify(f)(s) call site allocates no S => T closure (modify is inline). Fused compositions override it with a kernel that builds no carrier at all.

Attributes

Source
Optional.scala
inline override def replace(b: B): S => T

Attributes

Definition Classes
Source
Optional.scala
def reverseGet(s: S, b: B): T

Write b back into s: one tear, then rebuild; a miss passes s's T through. Optional.apply's optics call the user's reverseGet directly instead.

Write b back into s: one tear, then rebuild; a miss passes s's T through. Optional.apply's optics call the user's reverseGet directly instead.

Attributes

Source
Optional.scala

Inherited methods

def andThen[C, IB, G[_, _]](inner: Optic[A, Unit, C, IB, G])(using rc: ReadCompose[Affine, G]): rc.Out[S, C]

ANY outer ∘ read-only inner — the inner is honestly one-way (T = Unit: a Getter, AffineFold, or Fold), so only the two READ sides matter and the composite collapses to the read-only join of their strengths via compose.ReadCompose (Getter / PickFold / ForgetFold).

ANY outer ∘ read-only inner — the inner is honestly one-way (T = Unit: a Getter, AffineFold, or Fold), so only the two READ sides matter and the composite collapses to the read-only join of their strengths via compose.ReadCompose (Getter / PickFold / ForgetFold).

A trait member (not an extension in the companion) deliberately: once a receiver is statically one of the fused concrete classes, its andThen member overloads enter resolution and Scala 3 never falls back to extension methods when they all fail — the collapse must be in the member overload set to be reachable without an expected-type ascription.

Only the inner's T is pinned to Unit; its B stays free (IB) even though read-only inners always have B = Unit. That keeps this overload strictly LESS specific than the same-carrier andThen above (which accepts every argument this one does whenever B = Unit at the receiver), so a same-carrier read-only ∘ read-only call resolves unambiguously to the AssociativeFunctor path and this one fires exactly on the cross-seam cells the generic member cannot type.

Attributes

Inherited from:
Optic
Source
Optic.scala
inline def andThen[C, D](o: Optic[A, B, C, D, Affine]): Optic[S, T, C, D, Affine]

Compose with another optic under the shared carrier F. Requires AssociativeFunctor[F]. Cross-carrier composition (Lens → Optional, Lens → Traversal, …) goes through the Morph-summoning overload of this same method.

Compose with another optic under the shared carrier F. Requires AssociativeFunctor[F]. Cross-carrier composition (Lens → Optional, Lens → Traversal, …) goes through the Morph-summoning overload of this same method.

Attributes

Example
case class Address(street: String)
case class Person(address: Address)
val streetLens = lens[Person](_.address).andThen(lens[Address](_.street))
Inherited from:
Optic
Source
Optic.scala
def exists(p: A => Boolean)(s: S): Boolean

Attributes

Inherited from:
CanFold
Source
CanFold.scala
def foci(s: S): List[A]

Attributes

Inherited from:
CanFold
Source
CanFold.scala
def headOption(s: S): Option[A]

Attributes

Inherited from:
CanFold
Source
CanFold.scala
def length(s: S): Int

Attributes

Inherited from:
CanFold
Source
CanFold.scala
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