add focusing to Atom, generate Atom from QVar, deprecate Mut

Author: Oleg Nizhnik

concurrent/src/main/scala/tofu/concurrent/Atom.scala

@@ -1,9 +1,13 @@
 package tofu.concurrent
+import cats.{Applicative, Functor, Monad}
 import cats.effect.Sync
 import cats.effect.concurrent.Ref
+import tofu.Guarantee
 import tofu.concurrent.Atom.AtomByRef
 import tofu.higherKind.{RepresentableK, derived}
+import tofu.optics.Contains
 import tofu.syntax.monadic._
+import tofu.syntax.bracket._
 
 /** a middleground between cats.concurrent.Ref and zio.Ref */
 trait Atom[F[_], A] {
@@ -45,19 +49,47 @@ trait Atom[F[_], A] {
     * Like `tryModify` but does not complete until the update has been successfully made.
     */
   def modify[B](f: A => (A, B)): F[B]
-
 }
 
 object Atom {
   implicit def representableKInstance[A]: RepresentableK[Atom[*[_], A]] = derived.genRepresentableK[Atom[*[_], A]]
 
+  final implicit class AtomOps[F[_], A](private val self: Atom[F, A]) extends AnyVal {
+    def focused[B](bInA: A Contains B)(implicit F: Functor[F]): Atom[F, B] = self match {
+      case FocusedAtom(v, focus) => FocusedAtom(v, focus >> bInA)
+      case _                     => FocusedAtom(self, bInA)
+    }
+  }
+
   final case class AtomByRef[F[_], A](ref: Ref[F, A]) extends Atom[F, A] {
     override def get: F[A]                       = ref.get
     override def set(a: A): F[Unit]              = ref.set(a)
     override def getAndSet(a: A): F[A]           = ref.getAndSet(a)
     override def update(f: A => A): F[Unit]      = ref.update(f)
     override def modify[B](f: A => (A, B)): F[B] = ref.modify(f)
   }
+
+  final case class QAtom[F[_]: Applicative: Guarantee, A](qvar: QVar[F, A]) extends Atom[F, A] {
+    def get: F[A]                  = qvar.read
+    def set(a: A): F[Unit]         = getAndSet(a).void
+    def getAndSet(a: A): F[A]      = qvar.take.guaranteeAlways(qvar.put(a))
+    def update(f: A => A): F[Unit] = qvar.take.bracketIncomplete(a => qvar.put(f(a)))(qvar.put)
+    def modify[B](f: A => (A, B)): F[B] = qvar.take.bracketIncomplete { a =>
+      val (next, res) = f(a)
+      qvar.put(next) as res
+    }(qvar.put)
+  }
+
+  private[Atom] case class FocusedAtom[F[_]: Functor, A, B](v: Atom[F, A], focus: Contains[A, B]) extends Atom[F, B] {
+    def get: F[B]                  = v.get.map(focus.get)
+    def set(b: B): F[Unit]         = v.update(focus.set(_, b))
+    def getAndSet(b: B): F[B]      = v.modify(a => (focus.set(a, b), focus.get(a)))
+    def update(f: B => B): F[Unit] = v.update(focus.update(_, f))
+    def modify[C](f: B => (B, C)): F[C] = v.modify { a =>
+      val (b, c) = f(focus.get(a))
+      (focus.set(a, b), c)
+    }
+  }
 }
 
 trait MakeAtom[I[_], F[_]] {

concurrent/src/main/scala/tofu/concurrent/Mut.scala

@@ -10,6 +10,7 @@ import tofu.optics.Contains
 import tofu.syntax.bracket._
 
 /** simplified form of synchonized mutable variable, that could be satisfied both by MVar and Ref */
+@deprecated("use Atom / qvar.toAtom", since = "0.5.6")
 trait Mut[F[_], A] {
   def get: F[A]
   def update(f: A => A): F[Unit]
@@ -34,7 +35,7 @@ object Mut {
   }
 
   private[Mut] class FocusedMut[F[_], A, B](v: Mut[F, A], focus: Contains[A, B])(implicit F: Functor[F])
-      extends Mut[F, B] {
+    extends Mut[F, B] {
     def get: F[B]                   = v.get.map(focus.extract)
     def update(f: B => B): F[Unit]  = v.update(focus.update(_, f))
     override def set(b: B): F[Unit] = v.update(focus.set(_, b))

concurrent/src/main/scala/tofu/concurrent/QVar.scala

@@ -1,8 +1,11 @@
 package tofu.concurrent
-import cats.effect.{Concurrent, Sync}
 import cats.effect.concurrent.MVar
+import cats.effect.{Concurrent, Sync}
+import cats.{Applicative, Functor}
+import tofu.Guarantee
 import tofu.concurrent.QVar.QVarByMVar
 import tofu.higherKind.{RepresentableK, derived}
+import tofu.optics.Contains
 import tofu.syntax.monadic._
 
 /** a middleground between cats.concurrent.MVar and zio.Queue.bounded(1) */
@@ -57,6 +60,10 @@ trait QVar[F[_], A] {
 object QVar {
   implicit def representableK[A]: RepresentableK[QVar[*[_], A]] = derived.genRepresentableK[QVar[*[_], A]]
 
+  final implicit class QVarOps[F[_], A](private val self: QVar[F, A]) extends AnyVal {
+    def toAtom(implicit F: Applicative[F], FG: Guarantee[F]): Atom[F, A] = Atom.QAtom(self)
+  }
+
   final case class QVarByMVar[F[_], A](mvar: MVar[F, A]) extends QVar[F, A] {
     override def isEmpty: F[Boolean] = mvar.isEmpty
     override def put(a: A): F[Unit]  = mvar.put(a)