diff --git a/compat/src/main/scala-2.11_2.12/scala/collection/compat/PackageShared.scala b/compat/src/main/scala-2.11_2.12/scala/collection/compat/PackageShared.scala
index 8d811e20..a27a68de 100644
--- a/compat/src/main/scala-2.11_2.12/scala/collection/compat/PackageShared.scala
+++ b/compat/src/main/scala-2.11_2.12/scala/collection/compat/PackageShared.scala
@@ -360,7 +360,7 @@ private[compat] trait PackageShared {
     new RandomExtensions(self)
 }
 
-class ArrayExtensions(private val fact: Array.type) extends AnyVal {
+final class ArrayExtensions(private val fact: Array.type) extends AnyVal {
   def from[A: ClassTag](source: TraversableOnce[A]): Array[A] =
     source match {
       case it: Iterable[A] => it.toArray[A]
@@ -368,67 +368,67 @@ class ArrayExtensions(private val fact: Array.type) extends AnyVal {
     }
 }
 
-class ImmutableSortedMapExtensions(private val fact: i.SortedMap.type) extends AnyVal {
+final class ImmutableSortedMapExtensions(private val fact: i.SortedMap.type) extends AnyVal {
   def from[K: Ordering, V](source: TraversableOnce[(K, V)]): i.SortedMap[K, V] =
     build(i.SortedMap.newBuilder[K, V], source)
 }
 
-class ImmutableListMapExtensions(private val fact: i.ListMap.type) extends AnyVal {
+final class ImmutableListMapExtensions(private val fact: i.ListMap.type) extends AnyVal {
   def from[K, V](source: TraversableOnce[(K, V)]): i.ListMap[K, V] =
     build(i.ListMap.newBuilder[K, V], source)
 }
 
-class ImmutableHashMapExtensions(private val fact: i.HashMap.type) extends AnyVal {
+final class ImmutableHashMapExtensions(private val fact: i.HashMap.type) extends AnyVal {
   def from[K, V](source: TraversableOnce[(K, V)]): i.HashMap[K, V] =
     build(i.HashMap.newBuilder[K, V], source)
 }
 
-class ImmutableTreeMapExtensions(private val fact: i.TreeMap.type) extends AnyVal {
+final class ImmutableTreeMapExtensions(private val fact: i.TreeMap.type) extends AnyVal {
   def from[K: Ordering, V](source: TraversableOnce[(K, V)]): i.TreeMap[K, V] =
     build(i.TreeMap.newBuilder[K, V], source)
 }
 
-class ImmutableIntMapExtensions(private val fact: i.IntMap.type) extends AnyVal {
+final class ImmutableIntMapExtensions(private val fact: i.IntMap.type) extends AnyVal {
   def from[V](source: TraversableOnce[(Int, V)]): i.IntMap[V] =
     build(i.IntMap.canBuildFrom[Int, V](), source)
 }
 
-class ImmutableLongMapExtensions(private val fact: i.LongMap.type) extends AnyVal {
+final class ImmutableLongMapExtensions(private val fact: i.LongMap.type) extends AnyVal {
   def from[V](source: TraversableOnce[(Long, V)]): i.LongMap[V] =
     build(i.LongMap.canBuildFrom[Long, V](), source)
 }
 
-class MutableLongMapExtensions(private val fact: m.LongMap.type) extends AnyVal {
+final class MutableLongMapExtensions(private val fact: m.LongMap.type) extends AnyVal {
   def from[V](source: TraversableOnce[(Long, V)]): m.LongMap[V] =
     build(m.LongMap.canBuildFrom[Long, V](), source)
 }
 
-class MutableHashMapExtensions(private val fact: m.HashMap.type) extends AnyVal {
+final class MutableHashMapExtensions(private val fact: m.HashMap.type) extends AnyVal {
   def from[K, V](source: TraversableOnce[(K, V)]): m.HashMap[K, V] =
     build(m.HashMap.canBuildFrom[K, V](), source)
 }
 
-class MutableListMapExtensions(private val fact: m.ListMap.type) extends AnyVal {
+final class MutableListMapExtensions(private val fact: m.ListMap.type) extends AnyVal {
   def from[K, V](source: TraversableOnce[(K, V)]): m.ListMap[K, V] =
     build(m.ListMap.canBuildFrom[K, V](), source)
 }
 
-class MutableMapExtensions(private val fact: m.Map.type) extends AnyVal {
+final class MutableMapExtensions(private val fact: m.Map.type) extends AnyVal {
   def from[K, V](source: TraversableOnce[(K, V)]): m.Map[K, V] =
     build(m.Map.canBuildFrom[K, V](), source)
 }
 
-class StreamExtensionMethods[A](private val stream: Stream[A]) extends AnyVal {
+final class StreamExtensionMethods[A](private val stream: Stream[A]) extends AnyVal {
   def lazyAppendedAll(as: => TraversableOnce[A]): Stream[A] = stream.append(as)
 }
 
-class SortedExtensionMethods[K, T <: Sorted[K, T]](private val fact: Sorted[K, T]) {
+final class SortedExtensionMethods[K, T <: Sorted[K, T]](private val fact: Sorted[K, T]) {
   def rangeFrom(from: K): T = fact.from(from)
   def rangeTo(to: K): T = fact.to(to)
   def rangeUntil(until: K): T = fact.until(until)
 }
 
-class SortedMapExtensionMethods[K, V](
+final class SortedMapExtensionMethods[K, V](
     private val self: collection.SortedMap[K, V]
 ) extends AnyVal {
 
@@ -437,7 +437,7 @@ class SortedMapExtensionMethods[K, V](
   def maxBefore(key: K): Option[(K, V)] = self.until(key).lastOption
 }
 
-class SortedSetExtensionMethods[A](
+final class SortedSetExtensionMethods[A](
     private val self: collection.SortedSet[A]
 ) extends AnyVal {
 
@@ -446,7 +446,7 @@ class SortedSetExtensionMethods[A](
   def maxBefore(key: A): Option[A] = self.until(key).lastOption
 }
 
-class IteratorExtensionMethods[A](private val self: c.Iterator[A]) extends AnyVal {
+final class IteratorExtensionMethods[A](private val self: c.Iterator[A]) extends AnyVal {
   def sameElements[B >: A](that: c.TraversableOnce[B]): Boolean = {
     self.sameElements(that.iterator)
   }
@@ -457,7 +457,7 @@ class IteratorExtensionMethods[A](private val self: c.Iterator[A]) extends AnyVa
   def tapEach[U](f: A => U): c.Iterator[A] = self.map(a => { f(a); a })
 }
 
-class TraversableOnceExtensionMethods[A](private val self: c.TraversableOnce[A]) extends AnyVal {
+final class TraversableOnceExtensionMethods[A](private val self: c.TraversableOnce[A]) extends AnyVal {
   def iterator: Iterator[A] = self.toIterator
 
   def minOption[B >: A](implicit ord: Ordering[B]): Option[A] = {
@@ -489,7 +489,7 @@ class TraversableOnceExtensionMethods[A](private val self: c.TraversableOnce[A])
   }
 }
 
-class TraversableExtensionMethods[A](private val self: c.Traversable[A]) extends AnyVal {
+final class TraversableExtensionMethods[A](private val self: c.Traversable[A]) extends AnyVal {
   def iterableFactory: GenericCompanion[Traversable] = self.companion
 
   def sizeCompare(otherSize: Int): Int = SizeCompareImpl.sizeCompareInt(self)(otherSize)
@@ -498,11 +498,11 @@ class TraversableExtensionMethods[A](private val self: c.Traversable[A]) extends
 
 }
 
-class SeqExtensionMethods[A](private val self: c.Seq[A]) extends AnyVal {
+final class SeqExtensionMethods[A](private val self: c.Seq[A]) extends AnyVal {
   def lengthIs: SizeCompareOps = new SizeCompareOps(self)
 }
 
-class SizeCompareOps private[compat] (private val it: c.Traversable[_]) extends AnyVal {
+final class SizeCompareOps private[compat] (private val it: c.Traversable[_]) extends AnyVal {
   import SizeCompareImpl._
 
   /** Tests if the size of the collection is less than some value. */
@@ -564,7 +564,7 @@ private object SizeCompareImpl {
     }
 }
 
-class TraversableLikeExtensionMethods[A, Repr](private val self: c.GenTraversableLike[A, Repr])
+final class TraversableLikeExtensionMethods[A, Repr](private val self: c.GenTraversableLike[A, Repr])
     extends AnyVal {
   def tapEach[U](f: A => U)(implicit bf: CanBuildFrom[Repr, A, Repr]): Repr =
     self.map(a => { f(a); a })
@@ -624,7 +624,7 @@ class TraversableLikeExtensionMethods[A, Repr](private val self: c.GenTraversabl
   }
 }
 
-class TrulyTraversableLikeExtensionMethods[El1, Repr1](
+final class TrulyTraversableLikeExtensionMethods[El1, Repr1](
     private val self: TraversableLike[El1, Repr1])
     extends AnyVal {
 
@@ -633,7 +633,7 @@ class TrulyTraversableLikeExtensionMethods[El1, Repr1](
   ): Tuple2Zipped[El1, Repr1, El2, Repr2] = new Tuple2Zipped((self, t2))
 }
 
-class Tuple2ZippedExtensionMethods[El1, Repr1, El2, Repr2](
+final class Tuple2ZippedExtensionMethods[El1, Repr1, El2, Repr2](
     private val self: Tuple2Zipped[El1, Repr1, El2, Repr2]) {
 
   def lazyZip[El3, Repr3, T3](t3: T3)(implicit
@@ -641,7 +641,7 @@ class Tuple2ZippedExtensionMethods[El1, Repr1, El2, Repr2](
     new Tuple3Zipped((self.colls._1, self.colls._2, t3))
 }
 
-class MapExtensionMethods[K, V](private val self: scala.collection.Map[K, V]) extends AnyVal {
+final class MapExtensionMethods[K, V](private val self: scala.collection.Map[K, V]) extends AnyVal {
 
   def foreachEntry[U](f: (K, V) => U): Unit = {
     self.foreach { case (k, v) => f(k, v) }
@@ -649,7 +649,7 @@ class MapExtensionMethods[K, V](private val self: scala.collection.Map[K, V]) ex
 
 }
 
-class ImmutableMapExtensionMethods[K, V](private val self: scala.collection.immutable.Map[K, V])
+final class ImmutableMapExtensionMethods[K, V](private val self: scala.collection.immutable.Map[K, V])
     extends AnyVal {
 
   def updatedWith[V1 >: V](key: K)(remappingFunction: (Option[V]) => Option[V1]): Map[K, V1] =
@@ -659,7 +659,7 @@ class ImmutableMapExtensionMethods[K, V](private val self: scala.collection.immu
     }
 }
 
-class MutableMapExtensionMethods[K, V](private val self: scala.collection.mutable.Map[K, V])
+final class MutableMapExtensionMethods[K, V](private val self: scala.collection.mutable.Map[K, V])
     extends AnyVal {
 
   def updateWith(key: K)(remappingFunction: (Option[V]) => Option[V]): Option[V] = {
@@ -672,7 +672,7 @@ class MutableMapExtensionMethods[K, V](private val self: scala.collection.mutabl
   }
 }
 
-class MapViewExtensionMethods[K, V, C <: scala.collection.Map[K, V]](
+final class MapViewExtensionMethods[K, V, C <: scala.collection.Map[K, V]](
     private val self: IterableView[(K, V), C])
     extends AnyVal {
 
@@ -693,23 +693,23 @@ class MapViewExtensionMethods[K, V, C <: scala.collection.Map[K, V]](
     self.filter { case (k, _) => p(k) }
 }
 
-class ImmutableQueueExtensionMethods[A](private val self: i.Queue[A]) extends AnyVal {
+final class ImmutableQueueExtensionMethods[A](private val self: i.Queue[A]) extends AnyVal {
   def enqueueAll[B >: A](iter: c.Iterable[B]): i.Queue[B] =
     self.enqueue(iter.to[i.Iterable])
 }
 
-class MutableQueueExtensionMethods[Element](private val self: m.Queue[Element]) extends AnyVal {
+final class MutableQueueExtensionMethods[Element](private val self: m.Queue[Element]) extends AnyVal {
   def enqueueAll(iter: c.Iterable[Element]): Unit =
     self.enqueue(iter.toIndexedSeq: _*)
 }
 
-class OptionCompanionExtensionMethods(private val fact: Option.type) extends AnyVal {
+final class OptionCompanionExtensionMethods(private val fact: Option.type) extends AnyVal {
   def when[A](cond: Boolean)(a: => A): Option[A] = if (cond) Some(a) else None
 
   @inline def unless[A](cond: Boolean)(a: => A): Option[A] = when(!cond)(a)
 }
 
-class GenericCompanionExtensionMethods[CC[X] <: GenTraversable[X]](
+final class GenericCompanionExtensionMethods[CC[X] <: GenTraversable[X]](
     private val companion: GenericCompanion[CC]) extends AnyVal {
   def unfold[A, S](init: S)(f: S => Option[(A, S)])(
       implicit cbf: CanBuildFrom[CC[A], A, CC[A]]