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

Fold

dev.constructive.eo.optics.Fold

object Fold

Constructors for Fold — read-only multi-focus optic, backed by Forget[F] (Forget[F][X, A] = F[A]). T = Unit rules out the write path; .foldMap is the consumption surface. Fold.select(p) narrows to a one-element Option stream. The build-only dual on the same carrier — assemble a T from an F-layer — is Unfold.

Both constructors return the concrete ForgetFold subclass so a hand-written Fold picks up its eager, carrier-free foldMap member (see ForgetFold.foldMap).

Attributes

Source: Fold.scala
Graph
Supertypes: class Object

trait Matchable

class Any
Self type: Fold.type

Members list

Grouped members

Constructors

Fold over any Foldable[F].

Attributes

Example

import cats.instances.list.given
val listFold = Fold[List, Int]
listFold.foldMap(identity[Int])(List(1, 2, 3))   // 6

Source

Fold.scala

Value members

Concrete methods

Filtering Fold — backed by Forget[Option]. @group Constructors

Attributes

Source: Fold.scala

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