Add Sequence.orEmpty #KT-16552 Fixed

libraries/stdlib/samples/test/samples/collections/sequences.kt

@@ -7,6 +7,7 @@ import kotlin.coroutines.experimental.buildSequence
 
 @RunWith(Enclosed::class)
 class Sequences {
+
     class Building {
 
         @Sample
@@ -158,6 +159,17 @@ class Sequences {
 
     }
 
+    class Usage {
+
+        @Sample
+        fun sequenceOrEmpty() {
+            val nullSequence: Sequence<Int>? = null
+            assertPrints(nullSequence.orEmpty().toList(), "[]")
+
+            val sequence: Sequence<Int>? = sequenceOf(1, 2, 3)
+            assertPrints(sequence.orEmpty().toList(), "[1, 2, 3]")
+        }
+    }
 
     class Transformations {
 

libraries/stdlib/src/kotlin/collections/Sequences.kt

@@ -47,6 +47,14 @@ private object EmptySequence : Sequence<Nothing>, DropTakeSequence<Nothing> {
     override fun take(n: Int) = EmptySequence
 }
 
+/**
+ * Returns this sequence if it's not `null` and the empty sequence otherwise.
+ * @sample samples.collections.Sequences.Usage.sequenceOrEmpty
+ */
+@SinceKotlin("1.3")
+@kotlin.internal.InlineOnly
+public inline fun <T> Sequence<T>?.orEmpty(): Sequence<T> = this ?: emptySequence()
+
 /**
  * Returns a sequence of all elements from all sequences in this sequence.
  *

libraries/stdlib/test/collections/SequenceTest.kt

@@ -543,6 +543,14 @@ public class SequenceTest {
         assertEquals(listOf("act", "wast", "test"), sequenceOf("act", "test", "wast").sortedWith(comparator).toList())
     }
 
+    @Test fun orEmpty() {
+        val s1: Sequence<Int>? = null
+        assertEquals(emptySequence(), s1.orEmpty())
+
+        val s2: Sequence<Int>? = sequenceOf(1)
+        assertEquals(s2, s2.orEmpty())
+    }
+
     /*
     test fun pairIterator() {
         val pairStr = (fibonacci() zip fibonacci().map { i -> i*2 }).joinToString(limit = 10)