Add Array.from extension for scala 2.11 and 2.12 (#658)

Author: RustedBones

compat/src/main/scala-2.11_2.12/scala/collection/compat/PackageShared.scala

@@ -272,6 +272,9 @@ private[compat] trait PackageShared {
     builder.result()
   }
 
+  implicit def toArrayExtensions(fact: Array.type): ArrayExtensions =
+    new ArrayExtensions(fact)
+
   implicit def toImmutableSortedMapExtensions(
       fact: i.SortedMap.type): ImmutableSortedMapExtensions =
     new ImmutableSortedMapExtensions(fact)
@@ -357,6 +360,14 @@ private[compat] trait PackageShared {
     new RandomExtensions(self)
 }
 
+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]
+      case _ => source.toIterator.toArray[A]
+    }
+}
+
 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)

compat/src/test/scala/test/scala/collection/CollectionTest.scala

@@ -56,6 +56,9 @@ class CollectionTest {
   @Test
   def testFrom: Unit = {
     val xs = List(1, 2, 3)
+    val a = Array.from(xs)
+    val aT: Array[Int] = a
+    assertTrue(Array(1, 2, 3).sameElements(a))
     val v = Vector.from(xs)
     val vT: Vector[Int] = v
     assertEquals(Vector(1, 2, 3), v)