Factor out strict implementations of transformation operations.

Add StrictOptimizedMapOps and StrictOptimizedSortedMapOps.

Only operations that were implemented more than once have been factored
out. Some other operations could be factored out so that they could
be reused by custom collection implementations.

Fixes scala/collection-strawman#325

src/library/scala/collection/Seq.scala

@@ -181,7 +181,9 @@ trait SeqOps[+A, +CC[_], +C] extends Any
 
   // Make `concat` an alias for `appendedAll` so that it benefits from performance
   // overrides of this method
-  @`inline` final override def concat[B >: A](suffix: Iterable[B]): CC[B] = appendedAll(suffix)
+  // TODO https://github.com/scala/bug/issues/10853 Uncomment final
+  @deprecatedOverriding("This method should be final, but is not due to scala/bug#10853", "2.13.0")
+  @`inline` /*final*/ override def concat[B >: A](suffix: Iterable[B]): CC[B] = appendedAll(suffix)
 
  /** Produces a new sequence which contains all elements of this $coll and also all elements of
    *  a given sequence. `xs union ys`  is equivalent to `xs ++ ys`.

src/library/scala/collection/SortedMap.scala

@@ -186,7 +186,7 @@ trait SortedMapOps[K, +V, +CC[X, Y] <: Map[X, Y] with SortedMapOps[X, Y, CC, _],
 }
 
 object SortedMapOps {
-  private final val ordMsg = "No implicit Ordering[${K2}] found to build a SortedMap[${K2}, ${V2}]. You may want to upcast to a Map[${K}, ${V}] first by calling `unsorted`."
+  private[collection] final val ordMsg = "No implicit Ordering[${K2}] found to build a SortedMap[${K2}, ${V2}]. You may want to upcast to a Map[${K}, ${V}] first by calling `unsorted`."
 
   /** Specializes `MapWithFilter` for sorted Map collections
     *

src/library/scala/collection/StrictOptimizedIterableOps.scala

@@ -5,9 +5,10 @@ import scala.annotation.unchecked.uncheckedVariance
 import scala.language.higherKinds
 
 /**
-  * Trait that overrides operations to take advantage of strict builders.
+  * Trait that overrides iterable operations to take advantage of strict builders.
   *
   * @tparam A  Elements type
+  * @tparam CC Collection type constructor
   * @tparam C  Collection type
   */
 trait StrictOptimizedIterableOps[+A, +CC[_], +C]
@@ -70,54 +71,23 @@ trait StrictOptimizedIterableOps[+A, +CC[_], +C]
   // the view-based implementations, but they turn out to be slightly faster because
   // a couple of indirection levels are removed
 
-  override def map[B](f: A => B): CC[B] = {
-    val b = iterableFactory.newBuilder[B]
-    val it = iterator
-    while (it.hasNext) {
-      b += f(it.next())
-    }
-    b.result()
-  }
+  override def map[B](f: A => B): CC[B] =
+    StrictOptimizedOps.map(iterator, iterableFactory.newBuilder, f)
 
-  override def flatMap[B](f: A => IterableOnce[B]): CC[B] = {
-    val b = iterableFactory.newBuilder[B]
-    val it = iterator
-    while (it.hasNext) {
-      b ++= f(it.next())
-    }
-    b.result()
-  }
+  override def flatMap[B](f: A => IterableOnce[B]): CC[B] =
+    StrictOptimizedOps.flatMap(iterator, iterableFactory.newBuilder, f)
 
-  override def collect[B](pf: PartialFunction[A, B]): CC[B] = {
-    val b = iterableFactory.newBuilder[B]
-    val it = iterator
-    while (it.hasNext) {
-      val elem = it.next()
-      if (pf.isDefinedAt(elem)) {
-        b += pf.apply(elem)
-      }
-    }
-    b.result()
-  }
+  override def concat[B >: A](suffix: Iterable[B]): CC[B] =
+    StrictOptimizedOps.concat(iterator, suffix.iterator, iterableFactory.newBuilder[B])
 
-  override def flatten[B](implicit toIterableOnce: A => IterableOnce[B]): CC[B] = {
-    val b = iterableFactory.newBuilder[B]
-    val it = iterator
-    while (it.hasNext) {
-      b ++= toIterableOnce(it.next())
-    }
-    b.result()
-  }
+  override def collect[B](pf: PartialFunction[A, B]): CC[B] =
+    StrictOptimizedOps.collect(iterator, iterableFactory.newBuilder, pf)
 
-  override def zip[B](that: Iterable[B]): CC[(A @uncheckedVariance, B)] = {
-    val b = iterableFactory.newBuilder[(A, B)]
-    val it1 = iterator
-    val it2 = that.iterator
-    while (it1.hasNext && it2.hasNext) {
-      b += ((it1.next(), it2.next()))
-    }
-    b.result()
-  }
+  override def flatten[B](implicit toIterableOnce: A => IterableOnce[B]): CC[B] =
+    StrictOptimizedOps.flatten(iterator, iterableFactory.newBuilder)
+
+  override def zip[B](that: Iterable[B]): CC[(A @uncheckedVariance, B)] =
+    StrictOptimizedOps.zip(iterator, that.iterator, iterableFactory.newBuilder[(A, B)])
 
   override def zipWithIndex: CC[(A @uncheckedVariance, Int)] = {
     val b = iterableFactory.newBuilder[(A, Int)]

src/library/scala/collection/StrictOptimizedMapOps.scala

@@ -0,0 +1,29 @@
+package scala.collection
+
+import scala.language.higherKinds
+
+/**
+  * Trait that overrides map operations to take advantage of strict builders.
+  *
+  * @tparam K  Type of keys
+  * @tparam V  Type of values
+  * @tparam CC Collection type constructor
+  * @tparam C  Collection type
+  */
+trait StrictOptimizedMapOps[K, +V, +CC[_, _] <: IterableOps[_, AnyConstr, _], +C]
+  extends MapOps[K, V, CC, C]
+    with StrictOptimizedIterableOps[(K, V), Iterable, C] {
+
+  override def map[K2, V2](f: ((K, V)) => (K2, V2)): CC[K2, V2] =
+    StrictOptimizedOps.map(iterator, mapFactory.newBuilder, f)
+
+  override def flatMap[K2, V2](f: ((K, V)) => IterableOnce[(K2, V2)]): CC[K2, V2] =
+    StrictOptimizedOps.flatMap(iterator, mapFactory.newBuilder, f)
+
+  override def concat[V2 >: V](suffix: Iterable[(K, V2)]): CC[K, V2] =
+    StrictOptimizedOps.concat(iterator, suffix.iterator, mapFactory.newBuilder)
+
+  override def collect[K2, V2](pf: PartialFunction[(K, V), (K2, V2)]): CC[K2, V2] =
+    StrictOptimizedOps.collect(iterator, mapFactory.newBuilder, pf)
+
+}

src/library/scala/collection/StrictOptimizedOps.scala

@@ -0,0 +1,109 @@
+package scala.collection
+
+/**
+  * Convenient implementations of transformation operations
+  * based on builders.
+  *
+  * All the methods defined here are expected to be called with
+  * freshly created iterators and builders.
+  */
+object StrictOptimizedOps {
+
+  /**
+    * @param it Iterator to map elements from
+    * @param b Builder to use to build the resulting collection
+    * @param f Element transformation function
+    * @tparam A Type of elements of the source collection (e.g. `Int`)
+    * @tparam B Type of elements of the resulting collection (e.g. `String`)
+    * @tparam C Type of the resulting collection (e.g. `List[String]`)
+    * @return The resulting collection
+    */
+  @inline def map[A, B, C](it: Iterator[A], b: mutable.Builder[B, C], f: A => B): C = {
+    while (it.hasNext) {
+      b += f(it.next())
+    }
+    b.result()
+  }
+
+  /**
+    * @param it Iterator to flatMap elements from
+    * @param b Builder to use to build the resulting collection
+    * @param f Element transformation function
+    * @tparam A Type of elements of the source collection (e.g. `Int`)
+    * @tparam B Type of elements of the resulting collection (e.g. `String`)
+    * @tparam C Type of the resulting collection (e.g. `List[String]`)
+    * @return The resulting collection
+    */
+  @inline def flatMap[A, B, C](it: Iterator[A], b: mutable.Builder[B, C], f: A => IterableOnce[B]): C = {
+    while (it.hasNext) {
+      b ++= f(it.next())
+    }
+    b.result()
+  }
+
+  /**
+    * @param it1 Iterator of the first collection
+    * @param it2 Iterator of the second collection
+    * @param b Builder to use to build the resulting collection
+    * @tparam A Type of elements (e.g. `Int`)
+    * @tparam C Type of the resulting collection (e.g. `List[Int]`)
+    * @return The resulting collection
+    */
+  @inline def concat[A, C](it1: Iterator[A], it2: Iterator[A], b: mutable.Builder[A, C]): C = {
+    b ++= it1
+    b ++= it2
+    b.result()
+  }
+
+  /**
+    * @param it Iterator to collect elements from
+    * @param b Builder to use to build the resulting collection
+    * @param pf Element transformation partial function
+    * @tparam A Type of elements of the source collection (e.g. `Int`)
+    * @tparam B Type of elements of the resulting collection (e.g. `String`)
+    * @tparam C Type of the resulting collection (e.g. `List[String]`)
+    * @return The resulting collection
+    */
+  @inline def collect[A, B, C](it: Iterator[A], b: mutable.Builder[B, C], pf: PartialFunction[A, B]): C = {
+    while (it.hasNext) {
+      val elem = it.next()
+      if (pf.isDefinedAt(elem)) {
+        b += pf.apply(elem)
+      }
+    }
+    b.result()
+  }
+
+  /**
+    * @param it Iterator to flatten elements from
+    * @param b Builder to use to build the resulting collection
+    * @param toIterableOnce Evidence that `A` can be seen as an `IterableOnce[B]`
+    * @tparam A Type of elements of the source collection (e.g. `List[Int]`)
+    * @tparam B Type of elements of the resulting collection (e.g. `Int`)
+    * @tparam C Type of the resulting collection (e.g. `List[Int]`)
+    * @return The resulting collection
+    */
+  @inline def flatten[A, B, C](it: Iterator[A], b: mutable.Builder[B, C])(implicit toIterableOnce: A => IterableOnce[B]): C = {
+    while (it.hasNext) {
+      b ++= toIterableOnce(it.next())
+    }
+    b.result()
+  }
+
+  /**
+    * @param it1 Iterator of the first collection
+    * @param it2 Iterator of the second collection
+    * @param b Builder to use to build the resulting collection
+    * @tparam A Type of elements of the first collection (e.g. `Int`)
+    * @tparam B Type of elements of the second collection (e.g. `String`)
+    * @tparam C Type of the resulting collection (e.g. `List[(Int, String)]`)
+    * @return The resulting collection
+    */
+  @inline def zip[A, B, C](it1: Iterator[A], it2: Iterator[B], b: mutable.Builder[(A, B), C]): C = {
+    while (it1.hasNext && it2.hasNext) {
+      b += ((it1.next(), it2.next()))
+    }
+    b.result()
+  }
+
+}

src/library/scala/collection/StrictOptimizedSeqOps.scala

@@ -8,8 +8,8 @@ import scala.language.higherKinds
   */
 trait StrictOptimizedSeqOps [+A, +CC[_], +C]
   extends Any
-    with SeqOps[A, CC, C]
-    with StrictOptimizedIterableOps[A, CC, C] {
+    with StrictOptimizedIterableOps[A, CC, C]
+    with SeqOps[A, CC, C] {
 
   override def distinctBy[B](f: A => B): C = {
     val builder = newSpecificBuilder
@@ -45,12 +45,8 @@ trait StrictOptimizedSeqOps [+A, +CC[_], +C]
     b.result()
   }
 
-  override def appendedAll[B >: A](suffix: Iterable[B]): CC[B] = {
-    val b = iterableFactory.newBuilder[B]
-    b ++= this
-    b ++= suffix
-    b.result()
-  }
+  override def appendedAll[B >: A](suffix: Iterable[B]): CC[B] =
+    StrictOptimizedOps.concat(iterator, suffix.iterator, iterableFactory.newBuilder)
 
   override def prependedAll[B >: A](prefix: Iterable[B]): CC[B] = {
     val b = iterableFactory.newBuilder[B]

src/library/scala/collection/StrictOptimizedSetOps.scala

@@ -0,0 +1,17 @@
+package scala.collection
+
+/**
+  * Trait that overrides set operations to take advantage of strict builders.
+  *
+  * @tparam A  Elements type
+  * @tparam CC Collection type constructor
+  * @tparam C  Collection type
+  */
+trait StrictOptimizedSetOps[A, +CC[_], +C <: SetOps[A, CC, C]]
+  extends SetOps[A, CC, C]
+    with StrictOptimizedIterableOps[A, CC, C] {
+
+  override def concat(that: Iterable[A]): C =
+    StrictOptimizedOps.concat(iterator, that.iterator, newSpecificBuilder)
+
+}

src/library/scala/collection/StrictOptimizedSortedMapOps.scala

@@ -0,0 +1,29 @@
+package scala.collection
+
+import scala.annotation.implicitNotFound
+
+/**
+  * Trait that overrides sorted map operations to take advantage of strict builders.
+  *
+  * @tparam K  Type of keys
+  * @tparam V  Type of values
+  * @tparam CC Collection type constructor
+  * @tparam C  Collection type
+  */
+trait StrictOptimizedSortedMapOps[K, +V, +CC[X, Y] <: Map[X, Y] with SortedMapOps[X, Y, CC, _], +C <: SortedMapOps[K, V, CC, C]]
+  extends SortedMapOps[K, V, CC, C]
+    with StrictOptimizedMapOps[K, V, Map, C] {
+
+  override def map[K2, V2](f: ((K, V)) => (K2, V2))(implicit @implicitNotFound(SortedMapOps.ordMsg) ordering: Ordering[K2]): CC[K2, V2] =
+    StrictOptimizedOps.map(iterator, sortedMapFactory.newBuilder, f)
+
+  override def flatMap[K2, V2](f: ((K, V)) => IterableOnce[(K2, V2)])(implicit @implicitNotFound(SortedMapOps.ordMsg) ordering: Ordering[K2]): CC[K2, V2] =
+    StrictOptimizedOps.flatMap(iterator, sortedMapFactory.newBuilder, f)
+
+  override def concat[V2 >: V](xs: Iterable[(K, V2)]): CC[K, V2] =
+    StrictOptimizedOps.concat(iterator, xs.iterator, sortedMapFactory.newBuilder)
+
+  override def collect[K2, V2](pf: PartialFunction[(K, V), (K2, V2)])(implicit @implicitNotFound(SortedMapOps.ordMsg) ordering: Ordering[K2]): CC[K2, V2] =
+    StrictOptimizedOps.collect(iterator, sortedMapFactory.newBuilder, pf)
+
+}

src/library/scala/collection/StrictOptimizedSortedSetOps.scala

@@ -6,48 +6,27 @@ import scala.annotation.implicitNotFound
 import scala.annotation.unchecked.uncheckedVariance
 import scala.language.higherKinds
 
+/**
+  * Trait that overrides sorted set operations to take advantage of strict builders.
+  *
+  * @tparam A  Elements type
+  * @tparam CC Collection type constructor
+  * @tparam C  Collection type
+  */
 trait StrictOptimizedSortedSetOps[A, +CC[X] <: SortedSet[X], +C <: SortedSetOps[A, CC, C]]
   extends SortedSetOps[A, CC, C]
-    with StrictOptimizedIterableOps[A, Set, C] {
-
-  override def map[B](f: A => B)(implicit @implicitNotFound(SortedSetOps.ordMsg) ev: Ordering[B]): CC[B] = {
-    val b = sortedIterableFactory.newBuilder[B]
-    val it = iterator
-    while (it.hasNext) {
-      b += f(it.next())
-    }
-    b.result()
-  }
-
-  override def flatMap[B](f: A => IterableOnce[B])(implicit @implicitNotFound(SortedSetOps.ordMsg) ev: Ordering[B]): CC[B] = {
-    val b = sortedIterableFactory.newBuilder[B]
-    val it = iterator
-    while (it.hasNext) {
-      b ++= f(it.next())
-    }
-    b.result()
-  }
-
-  override def zip[B](that: Iterable[B])(implicit @implicitNotFound(SortedSetOps.zipOrdMsg) ev: Ordering[(A @uncheckedVariance, B)]): CC[(A @uncheckedVariance, B)] = { // sound bcs of VarianceNot
-    val b = sortedIterableFactory.newBuilder[(A, B)]
-    val it1 = iterator
-    val it2 = that.iterator
-    while (it1.hasNext && it2.hasNext) {
-      b += ((it1.next(), it2.next()))
-    }
-    b.result()
-  }
-
-  override def collect[B](pf: PartialFunction[A, B])(implicit @implicitNotFound(SortedSetOps.ordMsg) ev: Ordering[B]): CC[B] = {
-    val b = sortedIterableFactory.newBuilder[B]
-    val it = iterator
-    while (it.hasNext) {
-      val elem = it.next()
-      if (pf.isDefinedAt(elem)) {
-        b += pf.apply(elem)
-      }
-    }
-    b.result()
-  }
+    with StrictOptimizedSetOps[A, Set, C] {
+
+  override def map[B](f: A => B)(implicit @implicitNotFound(SortedSetOps.ordMsg) ev: Ordering[B]): CC[B] =
+    StrictOptimizedOps.map(iterator, sortedIterableFactory.newBuilder, f)
+
+  override def flatMap[B](f: A => IterableOnce[B])(implicit @implicitNotFound(SortedSetOps.ordMsg) ev: Ordering[B]): CC[B] =
+    StrictOptimizedOps.flatMap(iterator, sortedIterableFactory.newBuilder, f)
+
+  override def zip[B](that: Iterable[B])(implicit @implicitNotFound(SortedSetOps.zipOrdMsg) ev: Ordering[(A @uncheckedVariance, B)]): CC[(A @uncheckedVariance, B)] =
+    StrictOptimizedOps.zip(iterator, that.iterator, sortedIterableFactory.newBuilder[(A, B)])
+
+  override def collect[B](pf: PartialFunction[A, B])(implicit @implicitNotFound(SortedSetOps.ordMsg) ev: Ordering[B]): CC[B] =
+    StrictOptimizedOps.collect(iterator, sortedIterableFactory.newBuilder, pf)
 
 }