From fbb567c11a23e2d6cb0e825863b234c969e3e2d8 Mon Sep 17 00:00:00 2001
From: Ilya Gorbunov <ilya.gorbunov@jetbrains.com>
Date: Mon, 6 Apr 2015 20:39:20 +0300
Subject: [PATCH] Iterator<T> can be converted to a sequence constrained to be
 one-time iterable.

---
 libraries/stdlib/src/kotlin/collections/Sequence.kt | 10 ++++++++++
 libraries/stdlib/test/collections/SequenceTest.kt   | 10 ++++++++++
 2 files changed, 20 insertions(+)

diff --git a/libraries/stdlib/src/kotlin/collections/Sequence.kt b/libraries/stdlib/src/kotlin/collections/Sequence.kt
index 23874680e53..155358f9b8f 100644
--- a/libraries/stdlib/src/kotlin/collections/Sequence.kt
+++ b/libraries/stdlib/src/kotlin/collections/Sequence.kt
@@ -30,6 +30,16 @@ public fun <T> streamOf(progression: Progression<T>): Stream<T> = object : Strea
     override fun iterator(): Iterator<T> = progression.iterator()
 }
 
+/**
+ * Creates a sequence that returns all values from this iterator. The sequence is constrained to be iterated only once.
+ */
+public fun <T> Iterator<T>.sequence(): Sequence<T> {
+    val iteratorSequence = object : Sequence<T> {
+        override fun iterator(): Iterator<T> = this@sequence
+    }
+    return iteratorSequence.constrainOnce()
+}
+
 /**
  * Creates a sequence that returns the specified values.
  */
diff --git a/libraries/stdlib/test/collections/SequenceTest.kt b/libraries/stdlib/test/collections/SequenceTest.kt
index f0c2fa31afe..087c20661c3 100644
--- a/libraries/stdlib/test/collections/SequenceTest.kt
+++ b/libraries/stdlib/test/collections/SequenceTest.kt
@@ -186,6 +186,16 @@ public class SequenceTest {
     }
 
 
+    test fun sequenceFromIterator() {
+        val list = listOf(3, 2, 1, 0)
+        val iterator = list.iterator()
+        val sequence = iterator.sequence()
+        assertEquals(list, sequence.toList())
+        fails {
+            sequence.toList()
+        }
+    }
+
     test fun makeSequenceOneTimeConstrained() {
         val sequence = sequenceOf(1, 2, 3, 4)
         sequence.toList()