Only define unapply

Author: nicolasstucki

library/src/scala/tasty/TypeTest.scala

@@ -14,8 +14,6 @@ package scala.tasty
 @scala.annotation.implicitNotFound(msg = "No TypeTest available for [${S}, ${T}]")
 trait TypeTest[S, T <: S] extends Serializable {
 
-  def isInstance(x: S): TypeTest.Result[x.type & T]
-
   /** A TypeTest[S, T] can serve as an extractor that matches only S of type T.
    *
    * The compiler tries to turn unchecked type tests in pattern matches into checked ones
@@ -24,18 +22,6 @@ trait TypeTest[S, T <: S] extends Serializable {
    * `SomeExtractor(...)` is turned into `tt(SomeExtractor(...))` if `T` in `SomeExtractor.unapply(x: T)`
    * is uncheckable, but we have an instance of `TypeTest[S, T]`.
    */
-  def unapply(x: S): Option[x.type & T] =
-    if isInstance(x).asInstanceOf[Boolean] then Some(x.asInstanceOf[x.type & T])
-    else None
-
-}
-
-object TypeTest {
-
-  opaque type Result[A] = Boolean
-
-  def success[A](x: A): Result[A] = true
-
-  def failure[A]: Result[A] = false
+  def unapply(x: S): Option[x.type & T]
 
 }

tests/neg-custom-args/fatal-warnings/type-test-paths-2.scala

@@ -15,8 +15,8 @@ object RI extends R {
   type Succ = Int
   type Idx = Int
   protected def typeTestOfSucc: TypeTest[Nat, Succ] = new {
-    def isInstance(x: Int): TypeTest.Result[x.type & Succ] =
-      if x > 0 then TypeTest.success(x) else TypeTest.failure
+    def unapply(x: Int): Option[x.type & Succ] =
+      if x > 0 then Some(x) else None
   }
   def n: Nat = 4
   def one: Succ = 1

tests/neg-custom-args/fatal-warnings/type-test-paths.scala

@@ -32,9 +32,9 @@ object T1 extends T {
   def x: X = false
   def y: Y = true
   protected def typeTestOfY: TypeTest[X, Y] = new {
-    def isInstance(x: X): TypeTest.Result[x.type & Y] = x match
-      case x: (true & x.type) => TypeTest.success(x)
-      case _ => TypeTest.failure
+    def unapply(x: X): Option[x.type & Y] = x match
+      case x: (true & x.type) => Some(x)
+      case _ => None
   }
 
 }

tests/run/type-test-binding.scala

@@ -10,8 +10,8 @@ sealed trait Foo {
   def f(y: Y) = println("ok")
 
   given TypeTest[X, Y] = new TypeTest {
-    def isInstance(x: X): TypeTest.Result[x.type & Y] =
-      TypeTest.success(x.asInstanceOf[x.type & Y])
+    def unapply(x: X): Option[x.type & Y] =
+      Some(x.asInstanceOf[x.type & Y])
   }
 
   object Z {

tests/run/type-test-nat.scala

@@ -56,15 +56,15 @@ object IntNums extends Peano {
   type Succ = Int
 
   protected def typeTestOfZero: TypeTest[Nat, Zero] = new {
-    def isInstance(x: Nat): TypeTest.Result[x.type & Zero] =
-      if x == 0 then TypeTest.success(x)
-      else TypeTest.failure
+    def unapply(x: Nat): Option[x.type & Zero] =
+      if x == 0 then Some(x)
+      else None
   }
 
   protected def typeTestOfSucc: TypeTest[Nat, Succ] = new {
-    def isInstance(x: Nat): TypeTest.Result[x.type & Succ] =
-      if x > 0 then TypeTest.success(x)
-      else TypeTest.failure
+    def unapply(x: Nat): Option[x.type & Succ] =
+      if x > 0 then Some(x)
+      else None
   }
 
   def safeDiv(m: Nat, n: Succ): (Nat, Nat) = (m / n, m % n)
@@ -92,15 +92,15 @@ object ClassNums extends Peano {
   type Succ = SuccClass
 
   protected def typeTestOfZero: TypeTest[Nat, Zero] = new {
-    def isInstance(x: Nat): TypeTest.Result[x.type & Zero] = x match
-      case x: (ZeroObject.type & x.type) => TypeTest.success(x)
-      case _ => TypeTest.failure
+    def unapply(x: Nat): Option[x.type & Zero] = x match
+      case x: (ZeroObject.type & x.type) => Some(x)
+      case _ => None
   }
 
   protected def typeTestOfSucc: TypeTest[Nat, Succ] = new {
-    def isInstance(x: Nat): TypeTest.Result[x.type & Succ] = x match
-      case x: (SuccClass & x.type) => TypeTest.success(x)
-      case _ => TypeTest.failure
+    def unapply(x: Nat): Option[x.type & Succ] = x match
+      case x: (SuccClass & x.type) => Some(x)
+      case _ => None
   }
 
   def safeDiv(m: Nat, n: Succ): (Nat, Nat) = {