Merge pull request #1828 from paulp/pr/stream-lengthCompare

SI-6415, Stream#lengthCompare

6 files changed, 71 insertions, 23 deletions

diff --git a/src/library/scala/collection/LinearSeqOptimized.scala b/src/library/scala/collection/LinearSeqOptimized.scala
index 0f0a405a85..81cccea519 100755
--- a/src/library/scala/collection/LinearSeqOptimized.scala
+++ b/src/library/scala/collection/LinearSeqOptimized.scala
@@ -12,6 +12,7 @@ import generic._
 import mutable.ListBuffer
 import immutable.List
 import scala.util.control.Breaks._
+import scala.annotation.tailrec
 
 /** A template trait for linear sequences of type `LinearSeq[A]`  which optimizes
  *  the implementation of several methods under the assumption of fast linear access.
@@ -247,14 +248,17 @@ trait LinearSeqOptimized[+A, +Repr <: LinearSeqOptimized[A, Repr]] extends Linea
   }
 
   override /*SeqLike*/
-  def lengthCompare(len: Int): Int =  {
-    var i = 0
-    var these = self
-    while (!these.isEmpty && i <= len) {
-      i += 1
-      these = these.tail
+  def lengthCompare(len: Int): Int = {
+    @tailrec def loop(i: Int, xs: Repr): Int = {
+      if (i == len)
+        if (xs.isEmpty) 0 else 1
+      else if (xs.isEmpty)
+        -1
+      else
+        loop(i + 1, xs.tail)
     }
-    i - len
+    if (len < 0) 1
+    else loop(0, this)
   }
 
   override /*SeqLike*/
diff --git a/src/library/scala/collection/SeqLike.scala b/src/library/scala/collection/SeqLike.scala
index f65e2ef9cd..1be0dba29f 100644
--- a/src/library/scala/collection/SeqLike.scala
+++ b/src/library/scala/collection/SeqLike.scala
@@ -84,13 +84,17 @@ trait SeqLike[+A, +Repr] extends Any with IterableLike[A, Repr] with GenSeqLike[
    *  if computing `length` is cheap.
    */
   def lengthCompare(len: Int): Int = {
-    var i = 0
-    val it = iterator
-    while (it.hasNext && i <= len) {
-      it.next()
-      i += 1
+    if (len < 0) 1
+    else {
+      var i = 0
+      val it = iterator
+      while (it.hasNext) {
+        if (i == len) return if (it.hasNext) 1 else 0
+        it.next()
+        i += 1
+      }
+      i - len
     }
-    i - len
   }
 
   override /*IterableLike*/ def isEmpty: Boolean = lengthCompare(0) == 0
diff --git a/test/files/run/streams.check b/test/files/run/streams.check
index 7f894052d9..db6d2eebab 100644
--- a/test/files/run/streams.check
+++ b/test/files/run/streams.check
@@ -1,5 +1,8 @@
 Stream()
 Stream()
+true
+true
+true
 
 Array(1)
 Stream(1, ?)
@@ -8,12 +11,21 @@ Stream()
 Stream()
 Stream(1)
 Stream()
+true
+true
+true
+true
 
 Array(1, 2)
 Stream(2)
 Stream()
 Stream(1, 2)
 Stream()
+true
+true
+true
+true
+true
 
 999
 512
@@ -23,3 +35,5 @@ Stream(100001, ?)
 true
 true
 705082704
+
+true
diff --git a/test/files/run/streams.scala b/test/files/run/streams.scala
index 51b4e5d76c..03b2622edd 100644
--- a/test/files/run/streams.scala
+++ b/test/files/run/streams.scala
@@ -2,6 +2,9 @@ object Test extends App {
   val s0: Stream[Int] = Stream.empty
   println(s0.take(1))
   println(s0.takeWhile(_ > 0))
+  println(s0.lengthCompare(-5) > 0)
+  println(s0.lengthCompare(0) == 0)
+  println(s0.lengthCompare(5) < 0)
   println
 
   val s1 = Stream.cons(1, Stream.empty)
@@ -12,6 +15,10 @@ object Test extends App {
   println(s1.drop(2))
   println(s1.drop(-1))
   println(s1.dropWhile(_ > 0))
+  println(s1.lengthCompare(-5) > 0)
+  println(s1.lengthCompare(0) > 0)
+  println(s1.lengthCompare(1) == 0)
+  println(s1.lengthCompare(5) < 0)
   println
 
   val s2 = s1.append(Stream.cons(2, Stream.empty))
@@ -20,6 +27,11 @@ object Test extends App {
   println(s2.drop(2))
   println(s2.drop(-1))
   println(s2.dropWhile(_ > 0))
+  println(s2.lengthCompare(-5) > 0)
+  println(s2.lengthCompare(0) > 0)
+  println(s2.lengthCompare(1) > 0)
+  println(s2.lengthCompare(2) == 0)
+  println(s2.lengthCompare(5) < 0)
   println
 
   val s3 = Stream.range(1, 1000) //100000 (ticket #153: Stackoverflow)
@@ -43,4 +55,12 @@ object Test extends App {
   println(Stream.from(1).take(size).foldLeft(0)(_ + _))
   val arr = new Array[Int](size)
   Stream.from(1).take(size).copyToArray(arr, 0)
+
+  println
+
+  // ticket #6415
+  lazy val x = { println("evaluated"); 1 }
+  val s4 = 0 #:: x #:: Stream.empty
+
+  println(s4.isDefinedAt(0))
 }
diff --git a/test/files/run/t2544.check b/test/files/run/t2544.check
index 716b146ac4..d19538dca3 100644
--- a/test/files/run/t2544.check
+++ b/test/files/run/t2544.check
@@ -2,8 +2,8 @@
 2
 3
 3
--2
--2
+-1
+-1
 1
 1
 0
diff --git a/test/files/run/t2544.scala b/test/files/run/t2544.scala
index 7e7cfeb357..6bee2f1082 100644
--- a/test/files/run/t2544.scala
+++ b/test/files/run/t2544.scala
@@ -1,19 +1,25 @@
 object Test {
   object Foo extends Seq[Int] {
     def apply(i: Int) = i
-    def length = 4
+    def length = 5
     def iterator = Iterator(0,1,2,3,4)
   }
+  def lengthEquiv(result: Int) = println(
+    if (result < 0) -1
+    else if (result == 0) 0
+    else 1
+  )
+
   def main(args: Array[String]) = {
     println(Foo indexWhere(_ >= 2,1))
     println(Foo.toList indexWhere(_ >= 2,1))
     println(Foo segmentLength(_ <= 3,1))
     println(Foo.toList segmentLength(_ <= 3,1))
-    println(Foo lengthCompare 7)
-    println(Foo.toList lengthCompare 7)
-    println(Foo lengthCompare 2)
-    println(Foo.toList lengthCompare 2)
-    println(Foo lengthCompare 5)
-    println(Foo.toList lengthCompare 5)
+    lengthEquiv(Foo lengthCompare 7)
+    lengthEquiv(Foo.toList lengthCompare 7)
+    lengthEquiv(Foo lengthCompare 2)
+    lengthEquiv(Foo.toList lengthCompare 2)
+    lengthEquiv(Foo lengthCompare 5)
+    lengthEquiv(Foo.toList lengthCompare 5)
   }
-}
\ No newline at end of file
+}