Implement Optics for ZRef #3258

adamgfraser · 2020-04-02T11:38:54Z

Adds support for optics to ZRef. Implements a new method foldS that allows access to the state in the modification function. This allows us to implement accessField and accessCase, which allow applying a lens or a prism to a ZRef, respectively. Also includes initial work on encoding of traversals.

Copying @Odomontois.

Odomontois · 2020-04-02T11:46:58Z

core/shared/src/main/scala/zio/ZRef.scala

    final def set(a: A): IO[EA, Unit] =
-      setEither(a).fold(ZIO.fail(_), value.set)
+      value.modify { s =>
+        setEither(a)(s) match {
+          case Left(e)  => (Left(e), s)
+          case Right(s) => (Right(()), s)
+        }
+      }.absolve

    final def setAsync(a: A): IO[EA, Unit] =
-      setEither(a).fold(ZIO.fail(_), value.setAsync)
+      value.modify { s =>
+        setEither(a)(s) match {
+          case Left(e)  => (Left(e), s)
+          case Right(s) => (Right(()), s)
+        }
+      }.absolve
+  }


This was the main reason to add another type for foldS result in my PR.
These implementations are clearly more complex than older one, which can be significant in the highly concurrent use case.
And setAsync loses ability to delay modification.
So I felt like it's good to keep a somewhat performant version for simple mappings.

Yes could definitely add this.

Updated to add subtype to optimize set and setAsync for derived ZRef instances where possible.

adamgfraser · 2020-04-02T11:55:40Z

core/shared/src/main/scala/zio/package.scala

  type Ref[A]      = ZRef[Nothing, Nothing, A, A]
  type ERef[+E, A] = ZRef[E, E, A, A]

+  type ZLens[-S, +T, +A, -B]      = (S => A, B => S => T)


We could be more polymorphic here, allowing each of these optics to have a get error and a set error here, but then we would need some constructors that make it easy for users to lift simple optics into these more polymorphic types.

This could also allow us to support some other types of optics such as partial isomorphisms from ZIO Config.

adamgfraser · 2020-04-02T11:57:49Z

core/shared/src/main/scala/zio/package.scala

+  type ZLens[-S, +T, +A, -B]      = (S => A, B => S => T)
+  type ZOptional[-S, +T, +A, -B]  = (S => Option[A], B => S => T)
+  type ZPrism[-S, +T, +A, -B]     = (S => Option[A], B => T)
+  type ZTraversal[-S, +T, +A, -B] = (S => List[A], List[B] => S => Option[T])


I'm encoding a traversal right now as a pair of functions S => List[A] and List[B] => S => Option[T]. The set operation can fail if the number of elements being set doesn't match the expected number of elements to be set in the structure.

adamgfraser · 2020-04-02T11:59:42Z

core/shared/src/main/scala/zio/ZRef.scala

+      self.fold(identity, identity, c => Right(prism._2(c)), b => prism._1(b).fold[Either[Unit, D]](Left(()))(Right(_)))
+  }
+
+  implicit class TraversalSyntax[A, B](private val self: ZRef[Unit, Unit, A, B]) extends AnyVal {


This one in particular feels like it could benefit from a more polymorphic encoding of the optics.

adamgfraser · 2020-04-02T21:57:16Z

@Odomontois Would you take a look at this when you get the chance? I revised to incorporate your point about retaining the performance of the original version where possible and made it more polymorphic to support a wide range of optics.

adamgfraser · 2020-04-03T09:50:57Z

Added support for using optics with transactional references.

adamgfraser · 2020-04-04T15:33:27Z

Added documentation.

jdegoes · 2020-04-04T15:51:58Z

core/shared/src/main/scala/zio/package.scala

  type Ref[A]      = ZRef[Nothing, Nothing, A, A]
  type ERef[+E, A] = ZRef[E, E, A, A]

+  type ZOptic[-SG, -SS, -B, +EG, +ES, +A, +T] = (SG => Either[EG, A], B => SS => Either[ES, T])


Suggested change

type ZOptic[-SG, -SS, -B, +EG, +ES, +A, +T] = (SG => Either[EG, A], B => SS => Either[ES, T])

/**

* A `ZOptic` is able to get and set a piece of a whole, possibly failing. In the most general possible case,

* the set / get types are distinct, and setting may fail with a different error than getting.

*

* See more specific type aliases for concrete examples of what optics can be used to do.

*/

type ZOptic[-GetWhole, -SetWholeBefore, -SetPiece, +GetError, +SetError, +GetPiece, +SetWholeAfter] =

(GetWhole => Either[GetError, GetPiece], SetPiece => SetWholeBefore => Either[SetError, SetWholeAfter])

?

😆

jdegoes · 2020-04-08T13:58:34Z

core/shared/src/main/scala/zio/ZRef.scala

+   * the state in transforming the `set` value. This is a more powerful version
+   * of `fold` but requires unifying the error types.
+   */
+  def foldS[EC >: EB, ED, C, D](


jdegoes

Looks fantastic! Good to merge after mdoc passes.

bmeesters · 2020-04-10T14:22:43Z

Hello @adamgfraser , as a random bystander I am just curious on why the optics have been pulled out. Seemed pretty cool!

adamgfraser · 2020-04-10T14:27:26Z

@bmeesters We are going to provide them as part of a separate zio-optics project. This will allow us to continue to evolve the API for this functionality after we guarantee binary compatibility for 1.0, fully explore what we can do with this without risk of bloating the core ZIO project, and allow users who want to use other optics implementations to do that. Look for more on this soon!

initial work

a83fae8

Odomontois reviewed Apr 2, 2020

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format

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adamgfraser commented Apr 2, 2020

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adamgfraser requested a review from jdegoes April 2, 2020 12:19

adamgfraser added 3 commits April 2, 2020 09:29

add subtype

81ec4c4

generalize

74fbc98

merge upstream changes

fa5b755

adamgfraser added 2 commits April 3, 2020 01:43

merge upstream changes

cf37aa9

support optics in STM

539ff8b

add documentation

da23e76

jdegoes reviewed Apr 4, 2020

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adamgfraser added 5 commits April 4, 2020 17:21

address review comments

e6cb74d

move to optics package

133090a

fix compilation error

559bb6a

add instances

cbc1008

fix Scala 2.11 compatibility issue

bfced65

adamgfraser requested a review from jdegoes April 8, 2020 00:10

generalize

11cb49f

jdegoes reviewed Apr 8, 2020

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adamgfraser added 2 commits April 9, 2020 00:22

address review comments

a0a0fd0

pull out optics

8592990

jdegoes previously approved these changes Apr 10, 2020

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fix documentation

8c0dc5b

adamgfraser dismissed jdegoes’s stale review via 8c0dc5b April 10, 2020 11:47

jdegoes approved these changes Apr 10, 2020

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jdegoes merged commit de6c8c4 into zio:master Apr 10, 2020

jdegoes mentioned this pull request Apr 10, 2020

Implemented lens-like ZRef focusing on state components #3257

Closed

adamgfraser deleted the zref branch April 13, 2020 15:13

-  type ZOptic[-SG, -SS, -B, +EG, +ES, +A, +T] = (SG => Either[EG, A], B => SS => Either[ES, T])
+  /**
+    * A `ZOptic` is able to get and set a piece of a whole, possibly failing. In the most general possible case,
+    * the set / get types are distinct, and setting may fail with a different error than getting.
+    *
+    * See more specific type aliases for concrete examples of what optics can be used to do.
+    */
+  type ZOptic[-GetWhole, -SetWholeBefore, -SetPiece, +GetError, +SetError, +GetPiece, +SetWholeAfter] =
+  (GetWhole => Either[GetError, GetPiece], SetPiece => SetWholeBefore => Either[SetError, SetWholeAfter])

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Implement Optics for ZRef #3258

Implement Optics for ZRef #3258

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adamgfraser commented Apr 2, 2020

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Odomontois Apr 2, 2020 •

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