From baa13bc3d39bbf44418611efec2a8dd0711c4d21 Mon Sep 17 00:00:00 2001
From: Hamza Remmal <hamza@remmal.net>
Date: Mon, 17 Nov 2025 13:33:31 +0100
Subject: [PATCH 1/4] chore: port all `toString` method in the Scala 2
 inherited stdlib to be nullary functions

---
 library/src/scala/Boolean.scala               |  2 +-
 library/src/scala/Byte.scala                  |  2 +-
 library/src/scala/Char.scala                  |  2 +-
 library/src/scala/Double.scala                |  2 +-
 library/src/scala/Float.scala                 |  2 +-
 library/src/scala/Int.scala                   |  2 +-
 library/src/scala/Long.scala                  |  2 +-
 library/src/scala/Predef.scala                |  4 ++--
 library/src/scala/Proxy.scala                 |  2 +-
 .../src/scala/ScalaReflectionException.scala  |  2 +-
 library/src/scala/Short.scala                 |  2 +-
 .../src/scala/UninitializedFieldError.scala   |  2 +-
 library/src/scala/Unit.scala                  |  2 +-
 library/src/scala/collection/ArrayOps.scala   |  2 +-
 library/src/scala/collection/Iterable.scala   |  2 +-
 library/src/scala/collection/Iterator.scala   |  2 +-
 library/src/scala/collection/LazyZipOps.scala |  6 +++---
 library/src/scala/collection/MapView.scala    |  2 +-
 library/src/scala/collection/StringOps.scala  |  4 ++--
 library/src/scala/collection/View.scala       |  2 +-
 .../scala/collection/concurrent/TrieMap.scala |  4 ++--
 .../scala/collection/immutable/HashMap.scala  |  4 ++--
 .../scala/collection/immutable/HashSet.scala  |  2 +-
 .../collection/immutable/NumericRange.scala   |  2 +-
 .../scala/collection/immutable/Range.scala    |  4 ++--
 .../collection/immutable/RedBlackTree.scala   |  2 +-
 .../scala/collection/immutable/Stream.scala   |  2 +-
 .../collection/immutable/TreeSeqMap.scala     |  2 +-
 .../scala/collection/immutable/Vector.scala   |  6 +++---
 .../collection/immutable/WrappedString.scala  |  2 +-
 .../collection/mutable/ArrayBuilder.scala     | 20 +++++++++----------
 .../mutable/CollisionProofHashMap.scala       |  4 ++--
 .../scala/collection/mutable/HashMap.scala    |  2 +-
 .../scala/collection/mutable/HashSet.scala    |  2 +-
 .../collection/mutable/RedBlackTree.scala     |  2 +-
 .../collection/mutable/StringBuilder.scala    |  2 +-
 .../collection/mutable/UnrolledBuffer.scala   |  2 +-
 library/src/scala/concurrent/Future.scala     |  2 +-
 .../scala/concurrent/duration/Duration.scala  |  8 ++++----
 .../src/scala/concurrent/impl/Promise.scala   |  4 ++--
 library/src/scala/io/Codec.scala              |  2 +-
 library/src/scala/math/BigDecimal.scala       |  2 +-
 library/src/scala/package.scala               |  2 +-
 library/src/scala/ref/Reference.scala         |  2 +-
 library/src/scala/ref/ReferenceQueue.scala    |  2 +-
 .../reflect/ClassManifestDeprecatedApis.scala |  4 ++--
 library/src/scala/reflect/ClassTag.scala      |  2 +-
 library/src/scala/reflect/Manifest.scala      |  8 ++++----
 library/src/scala/reflect/NoManifest.scala    |  2 +-
 .../src/scala/runtime/ArrayCharSequence.scala |  2 +-
 library/src/scala/runtime/LazyRef.scala       | 20 +++++++++----------
 library/src/scala/runtime/Tuple2Zipped.scala  |  2 +-
 library/src/scala/runtime/Tuple3Zipped.scala  |  2 +-
 library/src/scala/sys/PropImpl.scala          |  2 +-
 .../sys/process/ProcessBuilderImpl.scala      |  4 ++--
 library/src/scala/typeConstraints.scala       |  2 +-
 library/src/scala/util/DynamicVariable.scala  |  2 +-
 library/src/scala/util/matching/Regex.scala   |  6 +++---
 58 files changed, 97 insertions(+), 97 deletions(-)

diff --git a/library/src/scala/Boolean.scala b/library/src/scala/Boolean.scala
index 5df9184b5e30..fcffb481b294 100644
--- a/library/src/scala/Boolean.scala
+++ b/library/src/scala/Boolean.scala
@@ -136,7 +136,7 @@ object Boolean extends AnyValCompanion {
   def unbox(x: java.lang.Object): Boolean = ???
 
   /** The String representation of the scala.Boolean companion object. */
-  override def toString = "object scala.Boolean"
+  override def toString() = "object scala.Boolean"
 
 }
 
diff --git a/library/src/scala/Byte.scala b/library/src/scala/Byte.scala
index c1f0e81f746b..4411af029fc2 100644
--- a/library/src/scala/Byte.scala
+++ b/library/src/scala/Byte.scala
@@ -477,7 +477,7 @@ object Byte extends AnyValCompanion {
   def unbox(x: java.lang.Object): Byte = ???
 
   /** The String representation of the scala.Byte companion object. */
-  override def toString = "object scala.Byte"
+  override def toString() = "object scala.Byte"
   /** Language mandated coercions from Byte to "wider" types. */
   import scala.language.implicitConversions
   implicit def byte2short(x: Byte): Short = x.toShort
diff --git a/library/src/scala/Char.scala b/library/src/scala/Char.scala
index 06a6e186901b..2676676acf27 100644
--- a/library/src/scala/Char.scala
+++ b/library/src/scala/Char.scala
@@ -477,7 +477,7 @@ object Char extends AnyValCompanion {
   def unbox(x: java.lang.Object): Char = ???
 
   /** The String representation of the scala.Char companion object. */
-  override def toString = "object scala.Char"
+  override def toString() = "object scala.Char"
   /** Language mandated coercions from Char to "wider" types. */
   import scala.language.implicitConversions
   implicit def char2int(x: Char): Int = x.toInt
diff --git a/library/src/scala/Double.scala b/library/src/scala/Double.scala
index 57e99999198b..ee814f97be16 100644
--- a/library/src/scala/Double.scala
+++ b/library/src/scala/Double.scala
@@ -252,6 +252,6 @@ object Double extends AnyValCompanion {
   def unbox(x: java.lang.Object): Double = ???
 
   /** The String representation of the scala.Double companion object. */
-  override def toString = "object scala.Double"
+  override def toString() = "object scala.Double"
 }
 
diff --git a/library/src/scala/Float.scala b/library/src/scala/Float.scala
index 1f8b00886258..fc6cced40b5d 100644
--- a/library/src/scala/Float.scala
+++ b/library/src/scala/Float.scala
@@ -252,7 +252,7 @@ object Float extends AnyValCompanion {
   def unbox(x: java.lang.Object): Float = ???
 
   /** The String representation of the scala.Float companion object. */
-  override def toString = "object scala.Float"
+  override def toString() = "object scala.Float"
   /** Language mandated coercions from Float to "wider" types. */
   import scala.language.implicitConversions
   implicit def float2double(x: Float): Double = x.toDouble
diff --git a/library/src/scala/Int.scala b/library/src/scala/Int.scala
index a3fff7e991da..dcaa1d2ff828 100644
--- a/library/src/scala/Int.scala
+++ b/library/src/scala/Int.scala
@@ -477,7 +477,7 @@ object Int extends AnyValCompanion {
   def unbox(x: java.lang.Object): Int = ???
 
   /** The String representation of the scala.Int companion object. */
-  override def toString = "object scala.Int"
+  override def toString() = "object scala.Int"
   /** Language mandated coercions from Int to "wider" types. */
   import scala.language.implicitConversions
   @deprecated("Implicit conversion from Int to Float is dangerous because it loses precision. Write `.toFloat` instead.", "2.13.1")
diff --git a/library/src/scala/Long.scala b/library/src/scala/Long.scala
index 2561c1ec74c2..7c0643b0b2f4 100644
--- a/library/src/scala/Long.scala
+++ b/library/src/scala/Long.scala
@@ -474,7 +474,7 @@ object Long extends AnyValCompanion {
   def unbox(x: java.lang.Object): Long = ???
 
   /** The String representation of the scala.Long companion object. */
-  override def toString = "object scala.Long"
+  override def toString() = "object scala.Long"
   /** Language mandated coercions from Long to "wider" types. */
   import scala.language.implicitConversions
   @deprecated("Implicit conversion from Long to Float is dangerous because it loses precision. Write `.toFloat` instead.", "2.13.1")
diff --git a/library/src/scala/Predef.scala b/library/src/scala/Predef.scala
index 5cb4742bf168..3cad7f7f9b5f 100644
--- a/library/src/scala/Predef.scala
+++ b/library/src/scala/Predef.scala
@@ -442,7 +442,7 @@ object Predef extends LowPriorityImplicits {
     def length: Int                                     = sequenceOfChars.length
     def charAt(index: Int): Char                        = sequenceOfChars(index)
     def subSequence(start: Int, end: Int): CharSequence = new SeqCharSequence(sequenceOfChars.slice(start, end))
-    override def toString                               = sequenceOfChars.mkString
+    override def toString()                             = sequenceOfChars.mkString
   }
 
   /** @group char-sequence-wrappers */
@@ -453,7 +453,7 @@ object Predef extends LowPriorityImplicits {
     def length: Int                                     = arrayOfChars.length
     def charAt(index: Int): Char                        = arrayOfChars(index)
     def subSequence(start: Int, end: Int): CharSequence = new runtime.ArrayCharSequence(arrayOfChars, start, end)
-    override def toString                               = arrayOfChars.mkString
+    override def toString()                             = arrayOfChars.mkString
   }
 
   /** @group char-sequence-wrappers */
diff --git a/library/src/scala/Proxy.scala b/library/src/scala/Proxy.scala
index 5d70bc3bdd10..81f097a67c2e 100644
--- a/library/src/scala/Proxy.scala
+++ b/library/src/scala/Proxy.scala
@@ -36,7 +36,7 @@ trait Proxy extends Any {
       val x = that.asInstanceOf[AnyRef]
       (x eq this.asInstanceOf[AnyRef]) || (x eq self.asInstanceOf[AnyRef]) || (x.equals(self))
   }
-  override def toString = "" + self
+  override def toString() = "" + self
 }
 
 @deprecated("All members of this object are deprecated.", "2.13.0")
diff --git a/library/src/scala/ScalaReflectionException.scala b/library/src/scala/ScalaReflectionException.scala
index 9a36ad305488..0626c79363fe 100644
--- a/library/src/scala/ScalaReflectionException.scala
+++ b/library/src/scala/ScalaReflectionException.scala
@@ -6,4 +6,4 @@ import scala.language.`2.13`
 case class ScalaReflectionException(msg: String) extends Exception(msg)
 
 object ScalaReflectionException extends scala.runtime.AbstractFunction1[String, ScalaReflectionException]:
-  override def toString: String = "ScalaReflectionException"
+  override def toString(): String = "ScalaReflectionException"
diff --git a/library/src/scala/Short.scala b/library/src/scala/Short.scala
index 03b0929ea5ce..ed94d655d656 100644
--- a/library/src/scala/Short.scala
+++ b/library/src/scala/Short.scala
@@ -477,7 +477,7 @@ object Short extends AnyValCompanion {
   def unbox(x: java.lang.Object): Short = ???
 
   /** The String representation of the scala.Short companion object. */
-  override def toString = "object scala.Short"
+  override def toString() = "object scala.Short"
   /** Language mandated coercions from Short to "wider" types. */
   import scala.language.implicitConversions
   implicit def short2int(x: Short): Int = x.toInt
diff --git a/library/src/scala/UninitializedFieldError.scala b/library/src/scala/UninitializedFieldError.scala
index 8accced02391..d1530c6818f7 100644
--- a/library/src/scala/UninitializedFieldError.scala
+++ b/library/src/scala/UninitializedFieldError.scala
@@ -25,4 +25,4 @@ final case class UninitializedFieldError(msg: String) extends RuntimeException(m
 }
 
 object UninitializedFieldError extends scala.runtime.AbstractFunction1[String, UninitializedFieldError]:
-  override def toString: String = "UninitializedFieldError"
+  override def toString(): String = "UninitializedFieldError"
diff --git a/library/src/scala/Unit.scala b/library/src/scala/Unit.scala
index e7ad25073f50..ab5f1a9b4a3d 100644
--- a/library/src/scala/Unit.scala
+++ b/library/src/scala/Unit.scala
@@ -55,6 +55,6 @@ object Unit extends AnyValCompanion {
   def unbox(x: java.lang.Object): Unit = x.asInstanceOf[scala.runtime.BoxedUnit]
 
   /** The String representation of the scala.Unit companion object. */
-  override def toString = "object scala.Unit"
+  override def toString() = "object scala.Unit"
 }
 
diff --git a/library/src/scala/collection/ArrayOps.scala b/library/src/scala/collection/ArrayOps.scala
index 11078a63bbbd..a8897b1d26fe 100644
--- a/library/src/scala/collection/ArrayOps.scala
+++ b/library/src/scala/collection/ArrayOps.scala
@@ -60,7 +60,7 @@ object ArrayOps {
   private class ArrayView[A](xs: Array[A]) extends AbstractIndexedSeqView[A] {
     def length = xs.length
     def apply(n: Int) = xs(n)
-    override def toString: String = immutable.ArraySeq.unsafeWrapArray(xs).mkString("ArrayView(", ", ", ")")
+    override def toString(): String = immutable.ArraySeq.unsafeWrapArray(xs).mkString("ArrayView(", ", ", ")")
   }
 
   /** A lazy filtered array. No filtering is applied until one of `foreach`, `map` or `flatMap` is called. */
diff --git a/library/src/scala/collection/Iterable.scala b/library/src/scala/collection/Iterable.scala
index 1a1044839d33..1ab43667b871 100644
--- a/library/src/scala/collection/Iterable.scala
+++ b/library/src/scala/collection/Iterable.scala
@@ -78,7 +78,7 @@ trait Iterable[+A] extends IterableOnce[A]
     *            string consists of the `className` of this $coll, followed
     *            by all elements separated by commas and enclosed in parentheses.
     */
-  override def toString = mkString(className + "(", ", ", ")")
+  override def toString() = mkString(className + "(", ", ", ")")
 
   /** Analogous to `zip` except that the elements in each collection are not consumed until a strict operation is
     * invoked on the returned `LazyZip2` decorator.
diff --git a/library/src/scala/collection/Iterator.scala b/library/src/scala/collection/Iterator.scala
index 55aaf5469729..6fc53c3d7470 100644
--- a/library/src/scala/collection/Iterator.scala
+++ b/library/src/scala/collection/Iterator.scala
@@ -977,7 +977,7 @@ trait Iterator[+A] extends IterableOnce[A] with IterableOnceOps[A, Iterator, Ite
    *  @return `"<iterator>"`
    *  @note    Reuse: $preservesIterator
    */
-  override def toString = "<iterator>"
+  override def toString() = "<iterator>"
 
   @deprecated("Iterator.seq always returns the iterator itself", "2.13.0")
   def seq: this.type = this
diff --git a/library/src/scala/collection/LazyZipOps.scala b/library/src/scala/collection/LazyZipOps.scala
index 899227167fee..c91155128833 100644
--- a/library/src/scala/collection/LazyZipOps.scala
+++ b/library/src/scala/collection/LazyZipOps.scala
@@ -133,7 +133,7 @@ final class LazyZip2[+El1, +El2, C1] private[collection](src: C1, coll1: Iterabl
     }
   }
 
-  override def toString = s"$coll1.lazyZip($coll2)"
+  override def toString() = s"$coll1.lazyZip($coll2)"
 }
 
 object LazyZip2 {
@@ -273,7 +273,7 @@ final class LazyZip3[+El1, +El2, +El3, C1] private[collection](src: C1,
     }
   }
 
-  override def toString = s"$coll1.lazyZip($coll2).lazyZip($coll3)"
+  override def toString() = s"$coll1.lazyZip($coll2).lazyZip($coll3)"
 }
 
 object LazyZip3 {
@@ -415,7 +415,7 @@ final class LazyZip4[+El1, +El2, +El3, +El4, C1] private[collection](src: C1,
     }
   }
 
-  override def toString = s"$coll1.lazyZip($coll2).lazyZip($coll3).lazyZip($coll4)"
+  override def toString() = s"$coll1.lazyZip($coll2).lazyZip($coll3).lazyZip($coll4)"
 }
 
 object LazyZip4 {
diff --git a/library/src/scala/collection/MapView.scala b/library/src/scala/collection/MapView.scala
index 4b021acd5c05..67e81eccf6cc 100644
--- a/library/src/scala/collection/MapView.scala
+++ b/library/src/scala/collection/MapView.scala
@@ -68,7 +68,7 @@ trait MapView[K, +V]
 
   override def withFilter(p: ((K, V)) => Boolean): MapOps.WithFilter[K, V, View, ({ type l[X, Y] = View[(X, Y)] })#l]^{this, p} = new MapOps.WithFilter(this, p)
 
-  override def toString: String = super[View].toString
+  override def toString(): String = super[View].toString
 
   @nowarn("""cat=deprecation&origin=scala\.collection\.Iterable\.stringPrefix""")
   override protected def stringPrefix: String = "MapView"
diff --git a/library/src/scala/collection/StringOps.scala b/library/src/scala/collection/StringOps.scala
index 4445b27e9d07..f72d4553b560 100644
--- a/library/src/scala/collection/StringOps.scala
+++ b/library/src/scala/collection/StringOps.scala
@@ -1649,8 +1649,8 @@ final case class StringView(s: String) extends AbstractIndexedSeqView[Char] {
   def length = s.length
   @throws[StringIndexOutOfBoundsException]
   def apply(n: Int) = s.charAt(n)
-  override def toString: String = s"StringView($s)"
+  override def toString(): String = s"StringView($s)"
 }
 
 object StringView extends scala.runtime.AbstractFunction1[String, StringView]:
-  override def toString: String = "StringView"
+  override def toString(): String = "StringView"
diff --git a/library/src/scala/collection/View.scala b/library/src/scala/collection/View.scala
index f55f2e07578f..b74e9e5f7362 100644
--- a/library/src/scala/collection/View.scala
+++ b/library/src/scala/collection/View.scala
@@ -35,7 +35,7 @@ trait View[+A] extends Iterable[A] with IterableOps[A, View, View[A]] with Itera
 
   override def empty: scala.collection.View[A] = iterableFactory.empty
 
-  override def toString: String  = className + "(<not computed>)"
+  override def toString(): String  = className + "(<not computed>)"
 
   @nowarn("""cat=deprecation&origin=scala\.collection\.Iterable\.stringPrefix""")
   override protected def stringPrefix: String = "View"
diff --git a/library/src/scala/collection/concurrent/TrieMap.scala b/library/src/scala/collection/concurrent/TrieMap.scala
index 98641bcc680d..56fe8b6a17ea 100644
--- a/library/src/scala/collection/concurrent/TrieMap.scala
+++ b/library/src/scala/collection/concurrent/TrieMap.scala
@@ -446,7 +446,7 @@ private[concurrent] final class FailedNode[K, V](p: MainNode[K, V]) extends Main
 
   def knownSize: Int = throw new UnsupportedOperationException
 
-  override def toString: String = "FailedNode(%s)".format(p)
+  override def toString(): String = "FailedNode(%s)".format(p)
 }
 
 
@@ -643,7 +643,7 @@ private[collection] final class CNode[K, V](val bitmap: Int, val array: Array[Ba
 
   def string(lev: Int): String = "CNode %x\n%s".format(bitmap, array.map(_.string(lev + 1)).mkString("\n"))
 
-  override def toString = {
+  override def toString() = {
     def elems: Seq[String] = array.flatMap {
       case sn: SNode[K, V] @uc => Iterable.single(sn.kvPair._2.toString)
       case in: INode[K, V] @uc => Iterable.single(augmentString(in.toString).drop(14) + "(" + in.gen + ")")
diff --git a/library/src/scala/collection/immutable/HashMap.scala b/library/src/scala/collection/immutable/HashMap.scala
index f2d7b4bb45e7..b323357db2b7 100644
--- a/library/src/scala/collection/immutable/HashMap.scala
+++ b/library/src/scala/collection/immutable/HashMap.scala
@@ -1348,7 +1348,7 @@ private final class BitmapIndexedMapNode[K, +V](
   override def hashCode(): Int =
     throw new UnsupportedOperationException("Trie nodes do not support hashing.")
 
-  override def toString = s"${getClass.getName}@${Integer.toHexString(System.identityHashCode(this))}"
+  override def toString() = s"${getClass.getName}@${Integer.toHexString(System.identityHashCode(this))}"
 
   override def concat[V1 >: V](that: MapNode[K, V1], shift: Int): BitmapIndexedMapNode[K, V1] = that match {
     case bm: BitmapIndexedMapNode[K, V] @unchecked =>
@@ -2095,7 +2095,7 @@ private final class HashCollisionMapNode[K, +V ](
   override def hashCode(): Int =
     throw new UnsupportedOperationException("Trie nodes do not support hashing.")
 
-  override def toString = s"${getClass.getName}@${Integer.toHexString(System.identityHashCode(this))}"
+  override def toString() = s"${getClass.getName}@${Integer.toHexString(System.identityHashCode(this))}"
 
   override def cachedJavaKeySetHashCode: Int = size * hash
 
diff --git a/library/src/scala/collection/immutable/HashSet.scala b/library/src/scala/collection/immutable/HashSet.scala
index a042f6256c80..68162b655e77 100644
--- a/library/src/scala/collection/immutable/HashSet.scala
+++ b/library/src/scala/collection/immutable/HashSet.scala
@@ -1424,7 +1424,7 @@ private final class BitmapIndexedSetNode[A](
   override def hashCode(): Int =
     throw new UnsupportedOperationException("Trie nodes do not support hashing.")
 
-  override def toString: String = f"BitmapIndexedSetNode(size=$size, dataMap=$dataMap%x, nodeMap=$nodeMap%x)" // content=${scala.runtime.ScalaRunTime.stringOf(content)}
+  override def toString(): String = f"BitmapIndexedSetNode(size=$size, dataMap=$dataMap%x, nodeMap=$nodeMap%x)" // content=${scala.runtime.ScalaRunTime.stringOf(content)}
 
   override def copy(): BitmapIndexedSetNode[A] = {
     val contentClone = content.clone()
diff --git a/library/src/scala/collection/immutable/NumericRange.scala b/library/src/scala/collection/immutable/NumericRange.scala
index f5c29028b820..9968c424ce04 100644
--- a/library/src/scala/collection/immutable/NumericRange.scala
+++ b/library/src/scala/collection/immutable/NumericRange.scala
@@ -362,7 +362,7 @@ sealed class NumericRange[T](
       super.equals(other)
   }
 
-  override def toString: String = {
+  override def toString(): String = {
     val empty = if (isEmpty) "empty " else ""
     val preposition = if (isInclusive) "to" else "until"
     val stepped = if (step == 1) "" else s" by $step"
diff --git a/library/src/scala/collection/immutable/Range.scala b/library/src/scala/collection/immutable/Range.scala
index 612b551a5fd5..b85fc71f2772 100644
--- a/library/src/scala/collection/immutable/Range.scala
+++ b/library/src/scala/collection/immutable/Range.scala
@@ -531,7 +531,7 @@ sealed abstract class Range(
     if(length >= 2) MurmurHash3.rangeHash(start, step, lastElement)
     else super.hashCode
 
-  final override def toString: String = {
+  final override def toString(): String = {
     val preposition = if (isInclusive) "to" else "until"
     val stepped = if (step == 1) "" else s" by $step"
 
@@ -674,7 +674,7 @@ object Range {
   // we offer a partially constructed object.
   class Partial[T, U](private val f: T => U) extends AnyVal { self: Partial[T, U]^ =>
     def by(x: T): U = f(x)
-    override def toString = "Range requires step"
+    override def toString() = "Range requires step"
   }
 
   // Illustrating genericity with Int Range, which should have the same behavior
diff --git a/library/src/scala/collection/immutable/RedBlackTree.scala b/library/src/scala/collection/immutable/RedBlackTree.scala
index 8582ee0bb4fb..4bbba28b7ae5 100644
--- a/library/src/scala/collection/immutable/RedBlackTree.scala
+++ b/library/src/scala/collection/immutable/RedBlackTree.scala
@@ -582,7 +582,7 @@ private[collection] object RedBlackTree {
     //Note - only used in tests outside RedBlackTree
     @`inline` private[immutable] final def isRed = _count >= 0
 
-    override def toString: String = s"${if(isRed) "RedTree" else "BlackTree"}($key, $value, $left, $right)"
+    override def toString(): String = s"${if(isRed) "RedTree" else "BlackTree"}($key, $value, $left, $right)"
 
     //mutable APIs
     private[RedBlackTree] def makeImmutable: this.type = {
diff --git a/library/src/scala/collection/immutable/Stream.scala b/library/src/scala/collection/immutable/Stream.scala
index 05e1bcaf087a..9d88d2449663 100644
--- a/library/src/scala/collection/immutable/Stream.scala
+++ b/library/src/scala/collection/immutable/Stream.scala
@@ -331,7 +331,7 @@ sealed abstract class Stream[+A] extends AbstractSeq[A]
     *           - `"Stream(1, 2, 3, &lt;cycle&gt;)"`, an infinite stream that contains
     *             a cycle at the fourth element.
     */
-  override def toString = addStringNoForce(new JStringBuilder(className), "(", ", ", ")").toString
+  override def toString() = addStringNoForce(new JStringBuilder(className), "(", ", ", ")").toString
 
   @deprecated("Check .knownSize instead of .hasDefiniteSize for more actionable information (see scaladoc for details)", "2.13.0")
   override def hasDefiniteSize: Boolean = isEmpty || {
diff --git a/library/src/scala/collection/immutable/TreeSeqMap.scala b/library/src/scala/collection/immutable/TreeSeqMap.scala
index 3bb7c3d29f34..b5c00a7b7f74 100644
--- a/library/src/scala/collection/immutable/TreeSeqMap.scala
+++ b/library/src/scala/collection/immutable/TreeSeqMap.scala
@@ -473,7 +473,7 @@ object TreeSeqMap extends MapFactory[TreeSeqMap] {
     import scala.annotation.tailrec
     import scala.collection.generic.BitOperations.Int._
 
-    override final def toString: String = format
+    override final def toString(): String = format
     final def format: String = {
       val sb = new StringBuilder
       format(sb, "", "")
diff --git a/library/src/scala/collection/immutable/Vector.scala b/library/src/scala/collection/immutable/Vector.scala
index 25e2270874dc..d4180908d782 100644
--- a/library/src/scala/collection/immutable/Vector.scala
+++ b/library/src/scala/collection/immutable/Vector.scala
@@ -1390,7 +1390,7 @@ private final class VectorSliceBuilder(lo: Int, hi: Int) {
     }
   }
 
-  override def toString: String =
+  override def toString(): String =
     s"VectorSliceBuilder(lo=$lo, hi=$hi, len=$len, pos=$pos, maxDim=$maxDim)"
 
   private[immutable] def getSlices: Array[Array[AnyRef] | Null] = slices
@@ -1981,7 +1981,7 @@ final class VectorBuilder[A] extends ReusableBuilder[A, Vector[A]] {
     }
   }
 
-  override def toString: String =
+  override def toString(): String =
     s"VectorBuilder(len1=$len1, lenRest=$lenRest, offset=$offset, depth=$depth)"
 
   private[immutable] def getData: Array[Array[?]] = Array[Array[AnyRef]](
@@ -2257,7 +2257,7 @@ private final class NewVectorIterator[A](v: Vector[A], private var totalLength:
   private var sliceStart = 0 // absolute position
   private var sliceEnd = a1len // absolute position
 
-  //override def toString: String =
+  //override def toString(): String =
   //  s"NewVectorIterator(v=$v, totalLength=$totalLength, sliceCount=$sliceCount): a1len=$a1len, len1=$len1, i1=$i1, sliceEnd=$sliceEnd"
 
   @inline override def knownSize = len1 - i1
diff --git a/library/src/scala/collection/immutable/WrappedString.scala b/library/src/scala/collection/immutable/WrappedString.scala
index 38b2b0fc1e0d..0e59479ba940 100644
--- a/library/src/scala/collection/immutable/WrappedString.scala
+++ b/library/src/scala/collection/immutable/WrappedString.scala
@@ -54,7 +54,7 @@ final class WrappedString(private val self: String) extends AbstractSeq[Char] wi
     new WrappedString(self.substring(start, end))
   }
   override def length = self.length
-  override def toString = self
+  override def toString() = self
   override def view: StringView = new StringView(self)
 
   override def stepper[S <: Stepper[?]](implicit shape: StepperShape[Char, S]): S & EfficientSplit = {
diff --git a/library/src/scala/collection/mutable/ArrayBuilder.scala b/library/src/scala/collection/mutable/ArrayBuilder.scala
index 1b27496e554a..1ac7d7454388 100644
--- a/library/src/scala/collection/mutable/ArrayBuilder.scala
+++ b/library/src/scala/collection/mutable/ArrayBuilder.scala
@@ -153,7 +153,7 @@ object ArrayBuilder {
       case _ => false
     }
 
-    override def toString = "ArrayBuilder.ofRef"
+    override def toString() = "ArrayBuilder.ofRef"
   }
 
   /** A class for array builders for arrays of `byte`s. It can be reused. */
@@ -195,7 +195,7 @@ object ArrayBuilder {
       case _ => false
     }
 
-    override def toString = "ArrayBuilder.ofByte"
+    override def toString() = "ArrayBuilder.ofByte"
   }
 
   /** A class for array builders for arrays of `short`s. It can be reused. */
@@ -237,7 +237,7 @@ object ArrayBuilder {
       case _ => false
     }
 
-    override def toString = "ArrayBuilder.ofShort"
+    override def toString() = "ArrayBuilder.ofShort"
   }
 
   /** A class for array builders for arrays of `char`s. It can be reused. */
@@ -279,7 +279,7 @@ object ArrayBuilder {
       case _ => false
     }
 
-    override def toString = "ArrayBuilder.ofChar"
+    override def toString() = "ArrayBuilder.ofChar"
   }
 
   /** A class for array builders for arrays of `int`s. It can be reused. */
@@ -321,7 +321,7 @@ object ArrayBuilder {
       case _ => false
     }
 
-    override def toString = "ArrayBuilder.ofInt"
+    override def toString() = "ArrayBuilder.ofInt"
   }
 
   /** A class for array builders for arrays of `long`s. It can be reused. */
@@ -363,7 +363,7 @@ object ArrayBuilder {
       case _ => false
     }
 
-    override def toString = "ArrayBuilder.ofLong"
+    override def toString() = "ArrayBuilder.ofLong"
   }
 
   /** A class for array builders for arrays of `float`s. It can be reused. */
@@ -405,7 +405,7 @@ object ArrayBuilder {
       case _ => false
     }
 
-    override def toString = "ArrayBuilder.ofFloat"
+    override def toString() = "ArrayBuilder.ofFloat"
   }
 
   /** A class for array builders for arrays of `double`s. It can be reused. */
@@ -447,7 +447,7 @@ object ArrayBuilder {
       case _ => false
     }
 
-    override def toString = "ArrayBuilder.ofDouble"
+    override def toString() = "ArrayBuilder.ofDouble"
   }
 
   /** A class for array builders for arrays of `boolean`s. It can be reused. */
@@ -490,7 +490,7 @@ object ArrayBuilder {
       case _ => false
     }
 
-    override def toString = "ArrayBuilder.ofBoolean"
+    override def toString() = "ArrayBuilder.ofBoolean"
   }
 
   /** A class for array builders for arrays of `Unit` type. It can be reused. */
@@ -534,6 +534,6 @@ object ArrayBuilder {
 
     protected def resize(size: Int): Unit = capacity = size
 
-    override def toString = "ArrayBuilder.ofUnit"
+    override def toString() = "ArrayBuilder.ofUnit"
   }
 }
diff --git a/library/src/scala/collection/mutable/CollisionProofHashMap.scala b/library/src/scala/collection/mutable/CollisionProofHashMap.scala
index e2fb03cf14a5..5ff7576a78d6 100644
--- a/library/src/scala/collection/mutable/CollisionProofHashMap.scala
+++ b/library/src/scala/collection/mutable/CollisionProofHashMap.scala
@@ -800,7 +800,7 @@ object CollisionProofHashMap extends SortedMapFactory[CollisionProofHashMap] {
       @annotation.stableNull
       var parent: RBNode[K, V] | Null
     ) extends Node {
-    override def toString: String = "RBNode(" + key + ", " + hash + ", " + value + ", " + red + ", " + left + ", " + right + ")"
+    override def toString(): String = "RBNode(" + key + ", " + hash + ", " + value + ", " + red + ", " + left + ", " + right + ")"
 
     @tailrec def getNode(k: K, h: Int)(implicit ord: Ordering[K]): RBNode[K, V] | Null = {
       val cmp = compare(k, h, this)
@@ -870,7 +870,7 @@ object CollisionProofHashMap extends SortedMapFactory[CollisionProofHashMap] {
   /////////////////////////// Linked List Node
 
   private final class LLNode[K, V](var key: K, var hash: Int, var value: V, @annotation.stableNull var next: LLNode[K, V] | Null) extends Node {
-    override def toString = s"LLNode($key, $value, $hash) -> $next"
+    override def toString() = s"LLNode($key, $value, $hash) -> $next"
 
     private def eq(a: Any, b: Any): Boolean =
       if(a.asInstanceOf[AnyRef] eq null) b.asInstanceOf[AnyRef] eq null else a.asInstanceOf[AnyRef].equals(b)
diff --git a/library/src/scala/collection/mutable/HashMap.scala b/library/src/scala/collection/mutable/HashMap.scala
index e7451b02bede..d537921314af 100644
--- a/library/src/scala/collection/mutable/HashMap.scala
+++ b/library/src/scala/collection/mutable/HashMap.scala
@@ -655,7 +655,7 @@ object HashMap extends MapFactory[HashMap] {
       if(_next ne null) _next.foreachEntry(f)
     }
 
-    override def toString = s"Node($key, $value, $hash) -> $next"
+    override def toString() = s"Node($key, $value, $hash) -> $next"
   }
 }
 
diff --git a/library/src/scala/collection/mutable/HashSet.scala b/library/src/scala/collection/mutable/HashSet.scala
index 1db7a19b50c3..6c4a1b3a6c71 100644
--- a/library/src/scala/collection/mutable/HashSet.scala
+++ b/library/src/scala/collection/mutable/HashSet.scala
@@ -454,6 +454,6 @@ object HashSet extends IterableFactory[HashSet] {
       if(_next ne null) _next.foreach(f)
     }
 
-    override def toString = s"Node($key, $hash) -> $next"
+    override def toString() = s"Node($key, $hash) -> $next"
   }
 }
diff --git a/library/src/scala/collection/mutable/RedBlackTree.scala b/library/src/scala/collection/mutable/RedBlackTree.scala
index 9fdd27ebb00c..4df59dab4ff6 100644
--- a/library/src/scala/collection/mutable/RedBlackTree.scala
+++ b/library/src/scala/collection/mutable/RedBlackTree.scala
@@ -46,7 +46,7 @@ private[collection] object RedBlackTree {
       @annotation.stableNull
       var parent: Node[A, B] | Null
     ) {
-    override def toString: String = "Node(" + key + ", " + value + ", " + red + ", " + left + ", " + right + ")"
+    override def toString(): String = "Node(" + key + ", " + value + ", " + red + ", " + left + ", " + right + ")"
   }
 
   object Tree {
diff --git a/library/src/scala/collection/mutable/StringBuilder.scala b/library/src/scala/collection/mutable/StringBuilder.scala
index c283066eb64f..9d6077ebf604 100644
--- a/library/src/scala/collection/mutable/StringBuilder.scala
+++ b/library/src/scala/collection/mutable/StringBuilder.scala
@@ -109,7 +109,7 @@ final class StringBuilder(val underlying: java.lang.StringBuilder) extends Abstr
 
   def result() = underlying.toString
 
-  override def toString: String = result()
+  override def toString(): String = result()
 
   override def toArray[B >: Char](implicit ct: scala.reflect.ClassTag[B]) =
     ct.runtimeClass match {
diff --git a/library/src/scala/collection/mutable/UnrolledBuffer.scala b/library/src/scala/collection/mutable/UnrolledBuffer.scala
index bfc5582f5391..244f26fd8b6c 100644
--- a/library/src/scala/collection/mutable/UnrolledBuffer.scala
+++ b/library/src/scala/collection/mutable/UnrolledBuffer.scala
@@ -437,7 +437,7 @@ object UnrolledBuffer extends StrictOptimizedClassTagSeqFactory[UnrolledBuffer]
       tryMergeWithNext()
     }
 
-    override def toString: String =
+    override def toString(): String =
       array.take(size).mkString("Unrolled@%08x".format(System.identityHashCode(this)) + "[" + size + "/" + array.length + "](", ", ", ")") + " -> " + (if (next ne null) next.toString else "")
   }
 }
diff --git a/library/src/scala/concurrent/Future.scala b/library/src/scala/concurrent/Future.scala
index 7ca677721c28..1054b5834fab 100644
--- a/library/src/scala/concurrent/Future.scala
+++ b/library/src/scala/concurrent/Future.scala
@@ -640,7 +640,7 @@ object Future {
     override final def fallbackTo[U >: Nothing](that: Future[U]): Future[U] = this
     override final def mapTo[S](implicit tag: ClassTag[S]): Future[S] = this
     override final def andThen[U](pf: PartialFunction[Try[Nothing], U])(implicit executor: ExecutionContext): Future[Nothing] = this
-    override final def toString: String = "Future(<never>)"
+    override final def toString(): String = "Future(<never>)"
   }
 
   /** A Future which is completed with the Unit value.
diff --git a/library/src/scala/concurrent/duration/Duration.scala b/library/src/scala/concurrent/duration/Duration.scala
index 1757c74d02a3..29c62f88f0a6 100644
--- a/library/src/scala/concurrent/duration/Duration.scala
+++ b/library/src/scala/concurrent/duration/Duration.scala
@@ -177,7 +177,7 @@ object Duration {
    * '''''Use [[eq]] when checking an input of a method against this value.'''''
    */
   val Undefined: Infinite = new Infinite {
-    override def toString = "Duration.Undefined"
+    override def toString() = "Duration.Undefined"
     override def equals(other: Any): Boolean  = false
     override def +(other: Duration): Duration = this
     override def -(other: Duration): Duration = this
@@ -237,7 +237,7 @@ object Duration {
    * matching its semantics in arithmetic operations.
    */
   val Inf: Infinite = new Infinite  {
-    override def toString: String      = "Duration.Inf"
+    override def toString(): String      = "Duration.Inf"
     def compare(other: Duration): Int  = other match {
       case x if x eq Undefined => -1 // Undefined != Undefined
       case x if x eq this      => 0  // `case Inf` will include null checks in the byte code
@@ -254,7 +254,7 @@ object Duration {
    * matching its semantics in arithmetic operations.
    */
   val MinusInf: Infinite = new Infinite {
-    override def toString: String      = "Duration.MinusInf"
+    override def toString(): String      = "Duration.MinusInf"
     def compare(other: Duration): Int  = if (other eq this) 0 else -1
     def unary_- : Duration = Inf
     def toUnit(unit: TimeUnit): Double = Double.NegativeInfinity
@@ -604,7 +604,7 @@ final class FiniteDuration(val length: Long, val unit: TimeUnit) extends Duratio
   def fromNow: Deadline = Deadline.now + this
 
   private def unitString  = timeUnitName(unit) + ( if (length == 1) "" else "s" )
-  override def toString: String     = "" + length + " " + unitString
+  override def toString(): String     = "" + length + " " + unitString
 
   def compare(other: Duration): Int = other match {
     case x: FiniteDuration => toNanos compare x.toNanos
diff --git a/library/src/scala/concurrent/impl/Promise.scala b/library/src/scala/concurrent/impl/Promise.scala
index 181ce92b3480..6cb0f340a5c3 100644
--- a/library/src/scala/concurrent/impl/Promise.scala
+++ b/library/src/scala/concurrent/impl/Promise.scala
@@ -232,7 +232,7 @@ private[concurrent] object Promise {
       if (!get().isInstanceOf[Success[?]]) super.failed
       else Future.failedFailureFuture // Cached instance in case of already known success
 
-    @tailrec override final def toString: String = {
+    @tailrec override final def toString(): String = {
       val state = get()
       if (state.isInstanceOf[Try[?]]) "Future("+state+")"
       else if (state.isInstanceOf[Link[?]]) state.asInstanceOf[Link[T]].promise(this).toString
@@ -433,7 +433,7 @@ private[concurrent] object Promise {
   sealed trait Callbacks[-T]
 
   final class ManyCallbacks[-T](final val first: Transformation[T, ?], final val rest: Callbacks[T]) extends Callbacks[T] {
-    override final def toString: String = "ManyCallbacks"
+    override final def toString(): String = "ManyCallbacks"
   }
 
   private final val Noop = new Transformation[Nothing, Nothing](Xform_noop, null: (Any => Any) | Null, ExecutionContext.parasitic)
diff --git a/library/src/scala/io/Codec.scala b/library/src/scala/io/Codec.scala
index f1151e74c7fe..21418892af6b 100644
--- a/library/src/scala/io/Codec.scala
+++ b/library/src/scala/io/Codec.scala
@@ -46,7 +46,7 @@ class Codec(val charSet: Charset) {
   private var _onCodingException: Handler       = e => throw e
 
   /** The name of the Codec. */
-  override def toString: String = name
+  override def toString(): String = name
 
   // these methods can be chained to configure the variables above
   def onMalformedInput(newAction: Action): this.type              = { _onMalformedInput = newAction ; this }
diff --git a/library/src/scala/math/BigDecimal.scala b/library/src/scala/math/BigDecimal.scala
index 969829af8385..8f53190d4d2f 100644
--- a/library/src/scala/math/BigDecimal.scala
+++ b/library/src/scala/math/BigDecimal.scala
@@ -717,6 +717,6 @@ extends ScalaNumber with ScalaNumericConversions with Serializable with Ordered[
 
   /** Returns the decimal String representation of this BigDecimal.
    */
-  override def toString: String = this.bigDecimal.toString
+  override def toString(): String = this.bigDecimal.toString
 
 }
diff --git a/library/src/scala/package.scala b/library/src/scala/package.scala
index fe9ed612506e..ccf0187cb9ea 100644
--- a/library/src/scala/package.scala
+++ b/library/src/scala/package.scala
@@ -40,7 +40,7 @@ package object scala {
 
   // A dummy used by the specialization annotation.
   val AnyRef = new Specializable {
-    override def toString = "object AnyRef"
+    override def toString() = "object AnyRef"
   }
 
   @deprecated("Use IterableOnce instead of TraversableOnce", "2.13.0")
diff --git a/library/src/scala/ref/Reference.scala b/library/src/scala/ref/Reference.scala
index 549d23a162c1..bb13eede4f60 100644
--- a/library/src/scala/ref/Reference.scala
+++ b/library/src/scala/ref/Reference.scala
@@ -22,7 +22,7 @@ trait Reference[+T <: AnyRef] extends Function0[T] {
   def apply(): T
   /** return `Some` underlying if it hasn't been collected, otherwise `None` */
   def get: Option[T]
-  override def toString: String = get.map(_.toString).getOrElse("<deleted>")
+  override def toString(): String = get.map(_.toString).getOrElse("<deleted>")
   def clear(): Unit
   def enqueue(): Boolean
   def isEnqueued: Boolean
diff --git a/library/src/scala/ref/ReferenceQueue.scala b/library/src/scala/ref/ReferenceQueue.scala
index 827f17d43595..05d3db0f90b9 100644
--- a/library/src/scala/ref/ReferenceQueue.scala
+++ b/library/src/scala/ref/ReferenceQueue.scala
@@ -17,7 +17,7 @@ import scala.language.`2.13`
 class ReferenceQueue[+T <: AnyRef] {
 
   private[ref] val underlying: java.lang.ref.ReferenceQueue[? <: T] = new java.lang.ref.ReferenceQueue[T]
-  override def toString: String = underlying.toString
+  override def toString(): String = underlying.toString
 
   protected def Wrapper(jref: java.lang.ref.Reference[?] | Null): Option[Reference[T]] =
     jref match {
diff --git a/library/src/scala/reflect/ClassManifestDeprecatedApis.scala b/library/src/scala/reflect/ClassManifestDeprecatedApis.scala
index 80d6c3b6b483..5fe52e7b4ba1 100644
--- a/library/src/scala/reflect/ClassManifestDeprecatedApis.scala
+++ b/library/src/scala/reflect/ClassManifestDeprecatedApis.scala
@@ -216,7 +216,7 @@ object ClassManifestFactory {
   private class AbstractTypeClassManifest[T](prefix: OptManifest[?], name: String, clazz: jClass[?], args: OptManifest[?]*) extends ClassManifest[T] {
     override def runtimeClass = clazz
     override val typeArguments = args.toList
-    override def toString = prefix.toString+"#"+name+argString
+    override def toString() = prefix.toString+"#"+name+argString
   }
 
   /** ClassManifest for the abstract type `prefix # name`. `upperBound` is not
@@ -243,7 +243,7 @@ private class ClassTypeManifest[T](
   val runtimeClass: jClass[?],
   override val typeArguments: List[OptManifest[?]]) extends ClassManifest[T]
 {
-  override def toString =
+  override def toString() =
     (if (prefix.isEmpty) "" else prefix.get.toString+"#") +
     (if (runtimeClass.isArray) "Array" else runtimeClass.getName) +
     argString
diff --git a/library/src/scala/reflect/ClassTag.scala b/library/src/scala/reflect/ClassTag.scala
index 80ffb869c447..c0cc6caecfa1 100644
--- a/library/src/scala/reflect/ClassTag.scala
+++ b/library/src/scala/reflect/ClassTag.scala
@@ -82,7 +82,7 @@ trait ClassTag[T] extends ClassManifestDeprecatedApis[T] with Equals with Serial
   override def canEqual(x: Any) = x.isInstanceOf[ClassTag[?]]
   override def equals(x: Any) = x.isInstanceOf[ClassTag[?]] && this.runtimeClass == x.asInstanceOf[ClassTag[?]].runtimeClass
   override def hashCode = runtimeClass.##
-  override def toString = {
+  override def toString() = {
     def prettyprint(clazz: jClass[?]): String =
       if (clazz.isArray) s"Array[${prettyprint(clazz.getComponentType)}]" else
       clazz.getName
diff --git a/library/src/scala/reflect/Manifest.scala b/library/src/scala/reflect/Manifest.scala
index d3492a2bfe5a..da8f9f0ea136 100644
--- a/library/src/scala/reflect/Manifest.scala
+++ b/library/src/scala/reflect/Manifest.scala
@@ -412,7 +412,7 @@ object ManifestFactory {
   private class ClassTypeManifest[T](prefix: Option[Manifest[?]],
                                      val runtimeClass: Predef.Class[?],
                                      override val typeArguments: List[Manifest[?]]) extends Manifest[T] {
-    override def toString =
+    override def toString() =
       (if (prefix.isEmpty) "" else prefix.get.toString+"#") +
       (if (runtimeClass.isArray) "Array" else runtimeClass.getName) +
       argString
@@ -425,7 +425,7 @@ object ManifestFactory {
   private class AbstractTypeManifest[T](prefix: Manifest[?], name: String, upperBound: Predef.Class[?], args: scala.collection.Seq[Manifest[?]]) extends Manifest[T] {
     def runtimeClass = upperBound
     override val typeArguments = args.toList
-    override def toString = prefix.toString+"#"+name+argString
+    override def toString() = prefix.toString+"#"+name+argString
   }
 
   /** Manifest for the abstract type `prefix # name`. `upperBound` is not
@@ -437,7 +437,7 @@ object ManifestFactory {
   @SerialVersionUID(1L)
   private class WildcardManifest[T](lowerBound: Manifest[?], upperBound: Manifest[?]) extends Manifest[T] {
     def runtimeClass = upperBound.runtimeClass
-    override def toString =
+    override def toString() =
       "_" +
         (if (lowerBound eq Nothing) "" else " >: "+lowerBound) +
         (if (upperBound eq Nothing) "" else " <: "+upperBound)
@@ -453,7 +453,7 @@ object ManifestFactory {
     // We use an `Array` instead of a `Seq` for `parents` to avoid cyclic dependencies during deserialization
     // which can cause serialization proxies to leak and cause a ClassCastException.
     def runtimeClass = parents(0).runtimeClass
-    override def toString = parents.mkString(" with ")
+    override def toString() = parents.mkString(" with ")
   }
 
   /** Manifest for the intersection type `parents_0 with ... with parents_n`. */
diff --git a/library/src/scala/reflect/NoManifest.scala b/library/src/scala/reflect/NoManifest.scala
index 69a2b5e898d3..278449585760 100644
--- a/library/src/scala/reflect/NoManifest.scala
+++ b/library/src/scala/reflect/NoManifest.scala
@@ -20,5 +20,5 @@ import scala.language.`2.13`
 // TODO undeprecated until Scala reflection becomes non-experimental
 // @deprecated("This notion doesn't have a corresponding concept in 2.10, because scala.reflect.runtime.universe.TypeTag can capture arbitrary types. Use type tags instead of manifests, and there will be no need in opt manifests.", "2.10.0")
 object NoManifest extends OptManifest[Nothing] with Serializable {
-  override def toString = "<?>"
+  override def toString() = "<?>"
 }
diff --git a/library/src/scala/runtime/ArrayCharSequence.scala b/library/src/scala/runtime/ArrayCharSequence.scala
index 2ec482915c86..554b212f38ec 100644
--- a/library/src/scala/runtime/ArrayCharSequence.scala
+++ b/library/src/scala/runtime/ArrayCharSequence.scala
@@ -40,7 +40,7 @@ final class ArrayCharSequence(val xs: Array[Char], start: Int, end: Int) extends
       new ArrayCharSequence(xs, start1, start1 + newlen)
     }
   }
-  override def toString = {
+  override def toString() = {
     val start = math.max(this.start, 0)
     val end = math.min(xs.length, start + length)
 
diff --git a/library/src/scala/runtime/LazyRef.scala b/library/src/scala/runtime/LazyRef.scala
index 89246b53eda2..0ce72941d6da 100644
--- a/library/src/scala/runtime/LazyRef.scala
+++ b/library/src/scala/runtime/LazyRef.scala
@@ -29,7 +29,7 @@ class LazyRef[T] extends Serializable {
     value
   }
 
-  override def toString = s"LazyRef ${if (_initialized) s"of: ${_value}" else "thunk"}"
+  override def toString() = s"LazyRef ${if (_initialized) s"of: ${_value}" else "thunk"}"
 }
 
 @SerialVersionUID(1L)
@@ -45,7 +45,7 @@ class LazyBoolean extends Serializable {
     value
   }
 
-  override def toString = s"LazyBoolean ${if (_initialized) s"of: ${_value}" else "thunk"}"
+  override def toString() = s"LazyBoolean ${if (_initialized) s"of: ${_value}" else "thunk"}"
 }
 
 @SerialVersionUID(1L)
@@ -63,7 +63,7 @@ class LazyByte extends Serializable {
     value
   }
 
-  override def toString = s"LazyByte ${if (_initialized) s"of: ${_value}" else "thunk"}"
+  override def toString() = s"LazyByte ${if (_initialized) s"of: ${_value}" else "thunk"}"
 }
 
 @SerialVersionUID(1L)
@@ -79,7 +79,7 @@ class LazyChar extends Serializable {
     value
   }
 
-  override def toString = s"LazyChar ${if (_initialized) s"of: ${_value}" else "thunk"}"
+  override def toString() = s"LazyChar ${if (_initialized) s"of: ${_value}" else "thunk"}"
 }
 
 @SerialVersionUID(1L)
@@ -95,7 +95,7 @@ class LazyShort extends Serializable {
     value
   }
 
-  override def toString = s"LazyShort ${if (_initialized) s"of: ${_value}" else "thunk"}"
+  override def toString() = s"LazyShort ${if (_initialized) s"of: ${_value}" else "thunk"}"
 }
 
 @SerialVersionUID(1L)
@@ -111,7 +111,7 @@ class LazyInt extends Serializable {
     value
   }
 
-  override def toString = s"LazyInt ${if (_initialized) s"of: ${_value}" else "thunk"}"
+  override def toString() = s"LazyInt ${if (_initialized) s"of: ${_value}" else "thunk"}"
 }
 
 @SerialVersionUID(1L)
@@ -127,7 +127,7 @@ class LazyLong extends Serializable {
     value
   }
 
-  override def toString = s"LazyLong ${if (_initialized) s"of: ${_value}" else "thunk"}"
+  override def toString() = s"LazyLong ${if (_initialized) s"of: ${_value}" else "thunk"}"
 }
 
 @SerialVersionUID(1L)
@@ -143,7 +143,7 @@ class LazyFloat extends Serializable {
     value
   }
 
-  override def toString = s"LazyFloat ${if (_initialized) s"of: ${_value}" else "thunk"}"
+  override def toString() = s"LazyFloat ${if (_initialized) s"of: ${_value}" else "thunk"}"
 }
 
 @SerialVersionUID(1L)
@@ -159,7 +159,7 @@ class LazyDouble extends Serializable {
     value
   }
 
-  override def toString = s"LazyDouble ${if (_initialized) s"of: ${_value}" else "thunk"}"
+  override def toString() = s"LazyDouble ${if (_initialized) s"of: ${_value}" else "thunk"}"
 }
 
 @SerialVersionUID(1L)
@@ -169,5 +169,5 @@ class LazyUnit extends Serializable {
 
   def initialize(): Unit = _initialized = true
 
-  override def toString = s"LazyUnit${if (_initialized) "" else " thunk"}"
+  override def toString() = s"LazyUnit${if (_initialized) "" else " thunk"}"
 }
diff --git a/library/src/scala/runtime/Tuple2Zipped.scala b/library/src/scala/runtime/Tuple2Zipped.scala
index a32dc9f960e0..ff5f25122161 100644
--- a/library/src/scala/runtime/Tuple2Zipped.scala
+++ b/library/src/scala/runtime/Tuple2Zipped.scala
@@ -114,7 +114,7 @@ final class Tuple2Zipped[El1, It1 <: Iterable[El1], El2, It2 <: Iterable[El2]](p
     }
   }
 
-  override def toString = s"($coll1, $coll2).zipped"
+  override def toString() = s"($coll1, $coll2).zipped"
 }
 
 @deprecated("Use scala.collection.LazyZip2.", since = "2.13.0")
diff --git a/library/src/scala/runtime/Tuple3Zipped.scala b/library/src/scala/runtime/Tuple3Zipped.scala
index 84d07fe61340..c997f6f756c5 100644
--- a/library/src/scala/runtime/Tuple3Zipped.scala
+++ b/library/src/scala/runtime/Tuple3Zipped.scala
@@ -123,7 +123,7 @@ final class Tuple3Zipped[El1, It1 <: Iterable[El1], El2, It2 <: Iterable[El2], E
     }
   }
 
-  override def toString = s"($coll1, $coll2, $coll3).zipped"
+  override def toString() = s"($coll1, $coll2, $coll3).zipped"
 }
 
 @deprecated("Use scala.collection.LazyZip3.", since = "2.13.0")
diff --git a/library/src/scala/sys/PropImpl.scala b/library/src/scala/sys/PropImpl.scala
index 455fb65f9a18..98d316877ae8 100644
--- a/library/src/scala/sys/PropImpl.scala
+++ b/library/src/scala/sys/PropImpl.scala
@@ -44,7 +44,7 @@ private[sys] class PropImpl[+T](val key: String, valueFn: String => T) extends P
   protected def underlying: mutable.Map[String, String | Null] = scala.sys.props
   protected def zero: T = null.asInstanceOf[T]
   private def getString = if (isSet) "currently: " + get else "unset"
-  override def toString = "%s (%s)".format(key, getString)
+  override def toString() = "%s (%s)".format(key, getString)
 }
 
 private[sys] abstract class CreatorImpl[+T](f: String => T) extends Prop.Creator[T] {
diff --git a/library/src/scala/sys/process/ProcessBuilderImpl.scala b/library/src/scala/sys/process/ProcessBuilderImpl.scala
index 02857c067cf3..19475f7f2253 100644
--- a/library/src/scala/sys/process/ProcessBuilderImpl.scala
+++ b/library/src/scala/sys/process/ProcessBuilderImpl.scala
@@ -96,7 +96,7 @@ private[process] trait ProcessBuilderImpl {
 
       new SimpleProcess(process, inThread, outThread :: errorThread)
     }
-    override def toString = p.command.toString
+    override def toString() = p.command.toString
     override def canPipeTo = true
   }
 
@@ -240,7 +240,7 @@ private[process] trait ProcessBuilderImpl {
 
     checkNotThis(a)
     checkNotThis(b)
-    override def toString = " ( " + a + " " + operatorString + " " + b + " ) "
+    override def toString() = " ( " + a + " " + operatorString + " " + b + " ) "
   }
 
   private[process] class PipedBuilder(
diff --git a/library/src/scala/typeConstraints.scala b/library/src/scala/typeConstraints.scala
index 3c7e15de67ca..fc549060cd13 100644
--- a/library/src/scala/typeConstraints.scala
+++ b/library/src/scala/typeConstraints.scala
@@ -160,7 +160,7 @@ object <:< {
     override def andThen[C](r: Any =:= C) = r
     override def liftCo    [F[_]] = asInstanceOf[F[Any] =:= F[Any]]
     override def liftContra[F[_]] = asInstanceOf[F[Any] =:= F[Any]]
-    override def toString = "generalized constraint"
+    override def toString() = "generalized constraint"
   }
 
   /** `A =:= A` for all `A` (equality is reflexive). This also provides implicit views `A <:< B`
diff --git a/library/src/scala/util/DynamicVariable.scala b/library/src/scala/util/DynamicVariable.scala
index afe61cfb73ff..03022c9d7b71 100644
--- a/library/src/scala/util/DynamicVariable.scala
+++ b/library/src/scala/util/DynamicVariable.scala
@@ -66,5 +66,5 @@ class DynamicVariable[T](init: T) {
     */
   def value_=(newval: T) = tl.set(newval)
 
-  override def toString: String = "DynamicVariable(" + value + ")"
+  override def toString(): String = "DynamicVariable(" + value + ")"
 }
diff --git a/library/src/scala/util/matching/Regex.scala b/library/src/scala/util/matching/Regex.scala
index f81d37d89e55..2ee22a960d19 100644
--- a/library/src/scala/util/matching/Regex.scala
+++ b/library/src/scala/util/matching/Regex.scala
@@ -596,7 +596,7 @@ class Regex private[matching](val pattern: Pattern, groupNames: String*) extends
   def regex: String = pattern.pattern
 
   /** The string defining the regular expression */
-  override def toString: String = regex
+  override def toString(): String = regex
 }
 
 /** A [[Regex]] that finds the first match when used in a pattern match.
@@ -719,7 +719,7 @@ object Regex {
     )
 
     /** The matched string; equivalent to `matched.toString`. */
-    override def toString: String = matched.nn
+    override def toString(): String = matched.nn
   }
 
   /** Provides information about a successful match. */
@@ -842,7 +842,7 @@ object Regex {
     }
 
     /** Report emptiness. */
-    override def toString: String = super[AbstractIterator].toString
+    override def toString(): String = super[AbstractIterator].toString
 
     // ensure we're at a match
     private def ensure(): Unit = nextSeen match {

From 45f2f40639f925ac8acee5f1709dc0688475a734 Mon Sep 17 00:00:00 2001
From: Hamza Remmal <hamza@remmal.net>
Date: Mon, 17 Nov 2025 13:38:09 +0100
Subject: [PATCH 2/4] chore: port all `hashCode` method in the Scala 2
 inherited stdlib to be nullary functions

---
 library/src/scala/Enumeration.scala           |  6 +++---
 library/src/scala/Proxy.scala                 |  2 +-
 library/src/scala/Symbol.scala                |  2 +-
 library/src/scala/collection/Iterator.scala   |  2 +-
 .../convert/JavaCollectionWrappers.scala      | 16 +++++++--------
 .../scala/collection/immutable/ArraySeq.scala | 20 +++++++++----------
 .../scala/collection/immutable/Range.scala    |  2 +-
 .../scala/collection/mutable/ArraySeq.scala   | 20 +++++++++----------
 .../scala/collection/mutable/HashMap.scala    |  4 ++--
 .../scala/collection/mutable/HashSet.scala    |  4 ++--
 .../collection/mutable/LinkedHashMap.scala    |  4 ++--
 .../collection/mutable/LinkedHashSet.scala    |  4 ++--
 .../scala/concurrent/duration/Duration.scala  |  2 +-
 library/src/scala/reflect/ClassTag.scala      |  2 +-
 library/src/scala/reflect/Manifest.scala      |  2 +-
 15 files changed, 46 insertions(+), 46 deletions(-)

diff --git a/library/src/scala/Enumeration.scala b/library/src/scala/Enumeration.scala
index c5b7905573ad..3f1caaba2c8b 100644
--- a/library/src/scala/Enumeration.scala
+++ b/library/src/scala/Enumeration.scala
@@ -98,11 +98,11 @@ abstract class Enumeration (initial: Int) extends Serializable {
 
   /** The name of this enumeration.
    */
-  override def toString: String =
+  override def toString(): String =
     getClass.getName
       .stripSuffix(MODULE_SUFFIX_STRING)
       .split('.')
-      .last 
+      .last
       .split(Regex.quote(NAME_JOIN_STRING))
       .last
 
@@ -241,7 +241,7 @@ abstract class Enumeration (initial: Int) extends Serializable {
       case that: Enumeration#Value  => (outerEnum eq that.outerEnum) && (id == that.id)
       case _                        => false
     }
-    override def hashCode: Int = id.##
+    override def hashCode(): Int = id.##
 
     /** Create a ValueSet which contains this value and another one */
     def + (v: Value): ValueSet = ValueSet(this, v)
diff --git a/library/src/scala/Proxy.scala b/library/src/scala/Proxy.scala
index 81f097a67c2e..f8d7462c34f6 100644
--- a/library/src/scala/Proxy.scala
+++ b/library/src/scala/Proxy.scala
@@ -29,7 +29,7 @@ import scala.language.`2.13`
 trait Proxy extends Any {
   def self: Any
 
-  override def hashCode: Int = self.hashCode
+  override def hashCode(): Int = self.hashCode
   override def equals(that: Any): Boolean = that match {
     case null  => false
     case _     =>
diff --git a/library/src/scala/Symbol.scala b/library/src/scala/Symbol.scala
index a61c366f4ae2..0890947c80fe 100644
--- a/library/src/scala/Symbol.scala
+++ b/library/src/scala/Symbol.scala
@@ -24,7 +24,7 @@ final class Symbol private (val name: String) extends Serializable {
 
   @throws(classOf[java.io.ObjectStreamException])
   private def readResolve(): Any = Symbol.apply(name)
-  override def hashCode = name.hashCode()
+  override def hashCode() = name.hashCode()
   override def equals(other: Any) = this eq other.asInstanceOf[AnyRef]
 }
 
diff --git a/library/src/scala/collection/Iterator.scala b/library/src/scala/collection/Iterator.scala
index 6fc53c3d7470..319337aa1014 100644
--- a/library/src/scala/collection/Iterator.scala
+++ b/library/src/scala/collection/Iterator.scala
@@ -898,7 +898,7 @@ trait Iterator[+A] extends IterableOnce[A] with IterableOnceOps[A, Iterator, Ite
       // to verify partnerhood we use reference equality on gap because
       // type testing does not discriminate based on origin.
       private def compareGap(queue: scala.collection.mutable.Queue[A]) = gap eq queue
-      override def hashCode = gap.hashCode()
+      override def hashCode() = gap.hashCode()
       override def equals(other: Any) = other match {
         case x: Partner   => x.compareGap(gap) && gap.isEmpty
         case _            => super.equals(other)
diff --git a/library/src/scala/collection/convert/JavaCollectionWrappers.scala b/library/src/scala/collection/convert/JavaCollectionWrappers.scala
index d54d639c5a4b..14827e454f19 100644
--- a/library/src/scala/collection/convert/JavaCollectionWrappers.scala
+++ b/library/src/scala/collection/convert/JavaCollectionWrappers.scala
@@ -41,7 +41,7 @@ private[collection] object JavaCollectionWrappers extends Serializable {
       case that: IteratorWrapper[_] => this.underlying == that.underlying
       case _ => false
     }
-    override def hashCode: Int = underlying.hashCode()
+    override def hashCode(): Int = underlying.hashCode()
   }
 
   @SerialVersionUID(3L)
@@ -52,7 +52,7 @@ private[collection] object JavaCollectionWrappers extends Serializable {
       case that: JIteratorWrapper[_] => this.underlying == that.underlying
       case _ => false
     }
-    override def hashCode: Int = underlying.hashCode()
+    override def hashCode(): Int = underlying.hashCode()
   }
 
   @SerialVersionUID(3L)
@@ -63,7 +63,7 @@ private[collection] object JavaCollectionWrappers extends Serializable {
       case that: JEnumerationWrapper[_] => this.underlying == that.underlying
       case _ => false
     }
-    override def hashCode: Int = underlying.hashCode()
+    override def hashCode(): Int = underlying.hashCode()
   }
 
   trait IterableWrapperTrait[A] extends ju.AbstractCollection[A] {
@@ -79,7 +79,7 @@ private[collection] object JavaCollectionWrappers extends Serializable {
       case that: IterableWrapper[_] => this.underlying == that.underlying
       case _ => false
     }
-    override def hashCode: Int = underlying.hashCode()
+    override def hashCode(): Int = underlying.hashCode()
   }
 
   @SerialVersionUID(3L)
@@ -94,7 +94,7 @@ private[collection] object JavaCollectionWrappers extends Serializable {
       case that: JIterableWrapper[_] => this.underlying == that.underlying
       case _ => false
     }
-    override def hashCode: Int = underlying.hashCode()
+    override def hashCode(): Int = underlying.hashCode()
   }
 
   @SerialVersionUID(3L)
@@ -111,7 +111,7 @@ private[collection] object JavaCollectionWrappers extends Serializable {
       case that: JCollectionWrapper[_] => this.underlying == that.underlying
       case _ => false
     }
-    override def hashCode: Int = underlying.hashCode()
+    override def hashCode(): Int = underlying.hashCode()
   }
 
   @SerialVersionUID(3L)
@@ -285,7 +285,7 @@ private[collection] object JavaCollectionWrappers extends Serializable {
             // specified in the javadocs of java.util.Map.Entry.hashCode
             //
             // See https://github.com/scala/bug/issues/10663
-            override def hashCode = {
+            override def hashCode() = {
               (if (k == null) 0 else k.hashCode()) ^
               (if (v == null) 0 else v.hashCode())
             }
@@ -552,7 +552,7 @@ private[collection] object JavaCollectionWrappers extends Serializable {
       case _ => false
     }
 
-    override def hashCode: Int = underlying.hashCode()
+    override def hashCode(): Int = underlying.hashCode()
   }
 
   @SerialVersionUID(3L)
diff --git a/library/src/scala/collection/immutable/ArraySeq.scala b/library/src/scala/collection/immutable/ArraySeq.scala
index e657cf8eda71..51a4f302fb16 100644
--- a/library/src/scala/collection/immutable/ArraySeq.scala
+++ b/library/src/scala/collection/immutable/ArraySeq.scala
@@ -332,7 +332,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
     def length: Int = unsafeArray.length
     @throws[ArrayIndexOutOfBoundsException]
     def apply(i: Int): T = unsafeArray(i)
-    override def hashCode = MurmurHash3.arraySeqHash(unsafeArray)
+    override def hashCode() = MurmurHash3.arraySeqHash(unsafeArray)
     override def equals(that: Any): Boolean = that match {
       case that: ofRef[_] =>
         Array.equals(
@@ -363,7 +363,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
     def length: Int = unsafeArray.length
     @throws[ArrayIndexOutOfBoundsException]
     def apply(i: Int): Byte = unsafeArray(i)
-    override def hashCode = MurmurHash3.arraySeqHash(unsafeArray)
+    override def hashCode() = MurmurHash3.arraySeqHash(unsafeArray)
     override def equals(that: Any) = that match {
       case that: ofByte => Arrays.equals(unsafeArray, that.unsafeArray)
       case _ => super.equals(that)
@@ -405,7 +405,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
     def length: Int = unsafeArray.length
     @throws[ArrayIndexOutOfBoundsException]
     def apply(i: Int): Short = unsafeArray(i)
-    override def hashCode = MurmurHash3.arraySeqHash(unsafeArray)
+    override def hashCode() = MurmurHash3.arraySeqHash(unsafeArray)
     override def equals(that: Any) = that match {
       case that: ofShort => Arrays.equals(unsafeArray, that.unsafeArray)
       case _ => super.equals(that)
@@ -447,7 +447,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
     def length: Int = unsafeArray.length
     @throws[ArrayIndexOutOfBoundsException]
     def apply(i: Int): Char = unsafeArray(i)
-    override def hashCode = MurmurHash3.arraySeqHash(unsafeArray)
+    override def hashCode() = MurmurHash3.arraySeqHash(unsafeArray)
     override def equals(that: Any) = that match {
       case that: ofChar => Arrays.equals(unsafeArray, that.unsafeArray)
       case _ => super.equals(that)
@@ -492,7 +492,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
     def length: Int = unsafeArray.length
     @throws[ArrayIndexOutOfBoundsException]
     def apply(i: Int): Int = unsafeArray(i)
-    override def hashCode = MurmurHash3.arraySeqHash(unsafeArray)
+    override def hashCode() = MurmurHash3.arraySeqHash(unsafeArray)
     override def equals(that: Any) = that match {
       case that: ofInt => Arrays.equals(unsafeArray, that.unsafeArray)
       case _ => super.equals(that)
@@ -534,7 +534,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
     def length: Int = unsafeArray.length
     @throws[ArrayIndexOutOfBoundsException]
     def apply(i: Int): Long = unsafeArray(i)
-    override def hashCode = MurmurHash3.arraySeqHash(unsafeArray)
+    override def hashCode() = MurmurHash3.arraySeqHash(unsafeArray)
     override def equals(that: Any) = that match {
       case that: ofLong => Arrays.equals(unsafeArray, that.unsafeArray)
       case _ => super.equals(that)
@@ -576,7 +576,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
     def length: Int = unsafeArray.length
     @throws[ArrayIndexOutOfBoundsException]
     def apply(i: Int): Float = unsafeArray(i)
-    override def hashCode = MurmurHash3.arraySeqHash(unsafeArray)
+    override def hashCode() = MurmurHash3.arraySeqHash(unsafeArray)
     override def equals(that: Any) = that match {
       case that: ofFloat =>
         val array = unsafeArray
@@ -618,7 +618,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
     def length: Int = unsafeArray.length
     @throws[ArrayIndexOutOfBoundsException]
     def apply(i: Int): Double = unsafeArray(i)
-    override def hashCode = MurmurHash3.arraySeqHash(unsafeArray)
+    override def hashCode() = MurmurHash3.arraySeqHash(unsafeArray)
     override def equals(that: Any) = that match {
       case that: ofDouble =>
         val array = unsafeArray
@@ -660,7 +660,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
     def length: Int = unsafeArray.length
     @throws[ArrayIndexOutOfBoundsException]
     def apply(i: Int): Boolean = unsafeArray(i)
-    override def hashCode = MurmurHash3.arraySeqHash(unsafeArray)
+    override def hashCode() = MurmurHash3.arraySeqHash(unsafeArray)
     override def equals(that: Any) = that match {
       case that: ofBoolean => Arrays.equals(unsafeArray, that.unsafeArray)
       case _ => super.equals(that)
@@ -699,7 +699,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
     def length: Int = unsafeArray.length
     @throws[ArrayIndexOutOfBoundsException]
     def apply(i: Int): Unit = unsafeArray(i)
-    override def hashCode = MurmurHash3.arraySeqHash(unsafeArray)
+    override def hashCode() = MurmurHash3.arraySeqHash(unsafeArray)
     override def equals(that: Any) = that match {
       case that: ofUnit => unsafeArray.length == that.unsafeArray.length
       case _ => super.equals(that)
diff --git a/library/src/scala/collection/immutable/Range.scala b/library/src/scala/collection/immutable/Range.scala
index b85fc71f2772..e62ce0c78a45 100644
--- a/library/src/scala/collection/immutable/Range.scala
+++ b/library/src/scala/collection/immutable/Range.scala
@@ -527,7 +527,7 @@ sealed abstract class Range(
       super.equals(other)
   }
 
-  final override def hashCode: Int =
+  final override def hashCode(): Int =
     if(length >= 2) MurmurHash3.rangeHash(start, step, lastElement)
     else super.hashCode
 
diff --git a/library/src/scala/collection/mutable/ArraySeq.scala b/library/src/scala/collection/mutable/ArraySeq.scala
index fe2c9d18ecad..f71ced69ecc3 100644
--- a/library/src/scala/collection/mutable/ArraySeq.scala
+++ b/library/src/scala/collection/mutable/ArraySeq.scala
@@ -143,7 +143,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
     def length: Int = array.length
     def apply(index: Int): T = array(index)
     def update(index: Int, elem: T): Unit = { array(index) = elem }
-    override def hashCode = MurmurHash3.arraySeqHash(array)
+    override def hashCode() = MurmurHash3.arraySeqHash(array)
     override def equals(that: Any) = that match {
       case that: ofRef[_] =>
         Array.equals(
@@ -166,7 +166,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
     def length: Int = array.length
     def apply(index: Int): Byte = array(index)
     def update(index: Int, elem: Byte): Unit = { array(index) = elem }
-    override def hashCode = MurmurHash3.arraySeqHash(array)
+    override def hashCode() = MurmurHash3.arraySeqHash(array)
     override def equals(that: Any) = that match {
       case that: ofByte => Arrays.equals(array, that.array)
       case _ => super.equals(that)
@@ -186,7 +186,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
     def length: Int = array.length
     def apply(index: Int): Short = array(index)
     def update(index: Int, elem: Short): Unit = { array(index) = elem }
-    override def hashCode = MurmurHash3.arraySeqHash(array)
+    override def hashCode() = MurmurHash3.arraySeqHash(array)
     override def equals(that: Any) = that match {
       case that: ofShort => Arrays.equals(array, that.array)
       case _ => super.equals(that)
@@ -206,7 +206,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
     def length: Int = array.length
     def apply(index: Int): Char = array(index)
     def update(index: Int, elem: Char): Unit = { array(index) = elem }
-    override def hashCode = MurmurHash3.arraySeqHash(array)
+    override def hashCode() = MurmurHash3.arraySeqHash(array)
     override def equals(that: Any) = that match {
       case that: ofChar => Arrays.equals(array, that.array)
       case _ => super.equals(that)
@@ -247,7 +247,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
     def length: Int = array.length
     def apply(index: Int): Int = array(index)
     def update(index: Int, elem: Int): Unit = { array(index) = elem }
-    override def hashCode = MurmurHash3.arraySeqHash(array)
+    override def hashCode() = MurmurHash3.arraySeqHash(array)
     override def equals(that: Any) = that match {
       case that: ofInt => Arrays.equals(array, that.array)
       case _ => super.equals(that)
@@ -267,7 +267,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
     def length: Int = array.length
     def apply(index: Int): Long = array(index)
     def update(index: Int, elem: Long): Unit = { array(index) = elem }
-    override def hashCode = MurmurHash3.arraySeqHash(array)
+    override def hashCode() = MurmurHash3.arraySeqHash(array)
     override def equals(that: Any) = that match {
       case that: ofLong => Arrays.equals(array, that.array)
       case _ => super.equals(that)
@@ -287,7 +287,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
     def length: Int = array.length
     def apply(index: Int): Float = array(index)
     def update(index: Int, elem: Float): Unit = { array(index) = elem }
-    override def hashCode = MurmurHash3.arraySeqHash(array)
+    override def hashCode() = MurmurHash3.arraySeqHash(array)
     override def equals(that: Any) = that match {
       case that: ofFloat =>
         val thatArray = that.array
@@ -313,7 +313,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
     def length: Int = array.length
     def apply(index: Int): Double = array(index)
     def update(index: Int, elem: Double): Unit = { array(index) = elem }
-    override def hashCode = MurmurHash3.arraySeqHash(array)
+    override def hashCode() = MurmurHash3.arraySeqHash(array)
     override def equals(that: Any) = that match {
       case that: ofDouble =>
         val thatArray = that.array
@@ -339,7 +339,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
     def length: Int = array.length
     def apply(index: Int): Boolean = array(index)
     def update(index: Int, elem: Boolean): Unit = { array(index) = elem }
-    override def hashCode = MurmurHash3.arraySeqHash(array)
+    override def hashCode() = MurmurHash3.arraySeqHash(array)
     override def equals(that: Any) = that match {
       case that: ofBoolean => Arrays.equals(array, that.array)
       case _ => super.equals(that)
@@ -356,7 +356,7 @@ object ArraySeq extends StrictOptimizedClassTagSeqFactory[ArraySeq] { self =>
     def length: Int = array.length
     def apply(index: Int): Unit = array(index)
     def update(index: Int, elem: Unit): Unit = { array(index) = elem }
-    override def hashCode = MurmurHash3.arraySeqHash(array)
+    override def hashCode() = MurmurHash3.arraySeqHash(array)
     override def equals(that: Any) = that match {
       case that: ofUnit => array.length == that.array.length
       case _ => super.equals(that)
diff --git a/library/src/scala/collection/mutable/HashMap.scala b/library/src/scala/collection/mutable/HashMap.scala
index d537921314af..9c557d88356b 100644
--- a/library/src/scala/collection/mutable/HashMap.scala
+++ b/library/src/scala/collection/mutable/HashMap.scala
@@ -578,12 +578,12 @@ class HashMap[K, V](initialCapacity: Int, loadFactor: Double)
   @nowarn("""cat=deprecation&origin=scala\.collection\.Iterable\.stringPrefix""")
   override protected def stringPrefix = "HashMap"
 
-  override def hashCode: Int = {
+  override def hashCode(): Int = {
     if (isEmpty) MurmurHash3.emptyMapHash
     else {
       val tupleHashIterator = new HashMapIterator[Any] {
         var hash: Int = 0
-        override def hashCode: Int = hash
+        override def hashCode(): Int = hash
         override protected def extract(nd: Node[K, V]): Any = {
           hash = MurmurHash3.tuple2Hash(unimproveHash(nd.hash), nd.value.##)
           this
diff --git a/library/src/scala/collection/mutable/HashSet.scala b/library/src/scala/collection/mutable/HashSet.scala
index 6c4a1b3a6c71..d4ee0e4f8ca1 100644
--- a/library/src/scala/collection/mutable/HashSet.scala
+++ b/library/src/scala/collection/mutable/HashSet.scala
@@ -385,13 +385,13 @@ final class HashSet[A](initialCapacity: Int, loadFactor: Double)
 
   override protected def className = "HashSet"
 
-  override def hashCode: Int = {
+  override def hashCode(): Int = {
     val setIterator = this.iterator
     val hashIterator: Iterator[Any] =
       if (setIterator.isEmpty) setIterator
       else new HashSetIterator[Any] {
         var hash: Int = 0
-        override def hashCode: Int = hash
+        override def hashCode(): Int = hash
         override protected def extract(nd: Node[A]): Any = {
           hash = unimproveHash(nd.hash)
           this
diff --git a/library/src/scala/collection/mutable/LinkedHashMap.scala b/library/src/scala/collection/mutable/LinkedHashMap.scala
index eda7ea733bcd..d3ce49179fad 100644
--- a/library/src/scala/collection/mutable/LinkedHashMap.scala
+++ b/library/src/scala/collection/mutable/LinkedHashMap.scala
@@ -455,12 +455,12 @@ class LinkedHashMap[K, V]
     }
   }
 
-  override def hashCode: Int = {
+  override def hashCode(): Int = {
     if (isEmpty) MurmurHash3.emptyMapHash
     else {
       val tupleHashIterator = new LinkedHashMapIterator[Any] {
         var hash: Int = 0
-        override def hashCode: Int = hash
+        override def hashCode(): Int = hash
         override def extract(nd: Entry): Any = {
           hash = MurmurHash3.tuple2Hash(unimproveHash(nd.hash), nd.value.##)
           this
diff --git a/library/src/scala/collection/mutable/LinkedHashSet.scala b/library/src/scala/collection/mutable/LinkedHashSet.scala
index 803af05c54c5..c424dd05a2ca 100644
--- a/library/src/scala/collection/mutable/LinkedHashSet.scala
+++ b/library/src/scala/collection/mutable/LinkedHashSet.scala
@@ -291,13 +291,13 @@ class LinkedHashSet[A]
     }
   }
 
-  override def hashCode: Int = {
+  override def hashCode(): Int = {
     val setHashIterator =
       if (isEmpty) this.iterator
       else {
         new LinkedHashSetIterator[Any] {
           var hash: Int = 0
-          override def hashCode: Int = hash
+          override def hashCode(): Int = hash
           override def extract(nd: Entry): Any = {
             hash = unimproveHash(nd.hash)
             this
diff --git a/library/src/scala/concurrent/duration/Duration.scala b/library/src/scala/concurrent/duration/Duration.scala
index 29c62f88f0a6..958388df3a79 100644
--- a/library/src/scala/concurrent/duration/Duration.scala
+++ b/library/src/scala/concurrent/duration/Duration.scala
@@ -739,5 +739,5 @@ final class FiniteDuration(val length: Long, val unit: TimeUnit) extends Duratio
     case x: FiniteDuration => toNanos == x.toNanos
     case _                 => super.equals(other)
   }
-  override def hashCode: Int = toNanos.toInt
+  override def hashCode(): Int = toNanos.toInt
 }
diff --git a/library/src/scala/reflect/ClassTag.scala b/library/src/scala/reflect/ClassTag.scala
index c0cc6caecfa1..1ebe2ed41196 100644
--- a/library/src/scala/reflect/ClassTag.scala
+++ b/library/src/scala/reflect/ClassTag.scala
@@ -81,7 +81,7 @@ trait ClassTag[T] extends ClassManifestDeprecatedApis[T] with Equals with Serial
   // case class accessories
   override def canEqual(x: Any) = x.isInstanceOf[ClassTag[?]]
   override def equals(x: Any) = x.isInstanceOf[ClassTag[?]] && this.runtimeClass == x.asInstanceOf[ClassTag[?]].runtimeClass
-  override def hashCode = runtimeClass.##
+  override def hashCode() = runtimeClass.##
   override def toString() = {
     def prettyprint(clazz: jClass[?]): String =
       if (clazz.isArray) s"Array[${prettyprint(clazz.getComponentType)}]" else
diff --git a/library/src/scala/reflect/Manifest.scala b/library/src/scala/reflect/Manifest.scala
index da8f9f0ea136..b1a23c8e4af0 100644
--- a/library/src/scala/reflect/Manifest.scala
+++ b/library/src/scala/reflect/Manifest.scala
@@ -65,7 +65,7 @@ trait Manifest[T] extends ClassManifest[T] with Equals {
     case m: Manifest[_] => (m canEqual this) && (this.runtimeClass == m.runtimeClass) && (this <:< m) && (m <:< this)
     case _              => false
   }
-  override def hashCode = this.runtimeClass.##
+  override def hashCode() = this.runtimeClass.##
 }
 
 /** The object `Manifest` defines factory methods for manifests.

From 1f7c1aa2ddd7d4079e700cf72eaf63cf8bbe2cc7 Mon Sep 17 00:00:00 2001
From: Hamza Remmal <hamza@remmal.net>
Date: Mon, 17 Nov 2025 13:45:33 +0100
Subject: [PATCH 3/4] chore: add regression test for #19616

---
 tests/pos/i19616.scala | 6 ++++++
 1 file changed, 6 insertions(+)
 create mode 100644 tests/pos/i19616.scala

diff --git a/tests/pos/i19616.scala b/tests/pos/i19616.scala
new file mode 100644
index 000000000000..ff0da9e4cebf
--- /dev/null
+++ b/tests/pos/i19616.scala
@@ -0,0 +1,6 @@
+def Test: Unit =
+  val sb = new StringBuilder
+  var key = ""
+  var map = Map.empty[String, String]
+  map += key -> sb.toString()
+  map += key -> sb.toString

From 8617d686a41ff6fc2759ce520c4d897f0aab7cfd Mon Sep 17 00:00:00 2001
From: Hamza Remmal <hamza@remmal.net>
Date: Wed, 19 Nov 2025 18:08:44 +0100
Subject: [PATCH 4/4] add explanation in `TupleXXL` for `toString and
 `hashCode`

---
 library/src/scala/runtime/TupleXXL.scala | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/library/src/scala/runtime/TupleXXL.scala b/library/src/scala/runtime/TupleXXL.scala
index 2da0cbb15396..a6d9ed4317a7 100644
--- a/library/src/scala/runtime/TupleXXL.scala
+++ b/library/src/scala/runtime/TupleXXL.scala
@@ -9,9 +9,13 @@ final class TupleXXL private (es: IArray[Object]) extends Product {
   def productArity: Int = es.length
   override def productPrefix: String = "Tuple"
 
+  // NOTE: For historical reasons, we cannot change this method
+  // to `def toString(): String`. See #24461 for more informations.
   override def toString: String =
     elems.asInstanceOf[Array[Object]].mkString("(", ",", ")")
 
+  // NOTE: For historical reasons, we cannot change this method
+  // to `def hashCode(): Int`. See #24461 for more informations.
   override def hashCode: Int =
     scala.runtime.ScalaRunTime._hashCode(this)