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Commit8f785ec

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Show that@nullout works as intended
Needs a restarr to work!The forwarder / alias `IterableOnceOps./:` uses `@nullOut` to clearthe `this` reference before calling `foldLeft`. The annotation isalso on the method itself to ensure mixin forwarders (generated inthe subclass) and the static mixin accessor (generated in the trait)null out the receiver before invoking `/:`.After removing `LazyList.foldLeft`, it inherits the implementationfrom LinearSeqOps. That method again uses `@nullOut` twice, onceto clear `this` when it's no longer needed, and once on the methodfor the generated accessors.I think we should *not* use `@nullOut` everywhere in the standardlibrary, only on methods that cannot be overridden in LazyList, like`/:`.`@nullOut` works correctly on `mkString` too, but unfortunately the`addString` override in LazyList prevents GC of processed elementsdue to cycle detection.
1 parent7be76ae commit8f785ec

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4 files changed

+14
-22
lines changed

4 files changed

+14
-22
lines changed

‎src/library/scala/collection/IterableOnce.scala

Lines changed: 10 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -755,7 +755,8 @@ trait IterableOnceOps[+A, +CC[_], +C] extends Any { this: IterableOnce[A] =>
755755
deffoldRight[B](z:B)(op: (A,B)=>B):B= reversed.foldLeft(z)((b, a)=> op(a, b))
756756

757757
@deprecated("Use foldLeft instead of /:","2.13.0")
758-
@`inline`finaldef/: [B](z:B)(op: (B,A)=>B):B= foldLeft[B](z)(op)
758+
@annotation.nullOut
759+
@`inline`finaldef/: [B](z:B)(op: (B,A)=>B):B= (this:@annotation.nullOut).foldLeft[B](z)(op)
759760

760761
@deprecated("Use foldRight instead of :\\","2.13.0")
761762
@`inline`finaldef:\ [B](z:B)(op: (A,B)=>B):B= foldRight[B](z)(op)
@@ -1313,9 +1314,10 @@ trait IterableOnceOps[+A, +CC[_], +C] extends Any { this: IterableOnce[A] =>
13131314
*
13141315
*@example `List(1, 2, 3).mkString("(", "; ", ")") = "(1; 2; 3)"`
13151316
*/
1317+
@annotation.nullOut
13161318
finaldefmkString(start:String,sep:String,end:String):String=
13171319
if (knownSize==0) start+ end
1318-
else addString(newStringBuilder(), start, sep, end).result()
1320+
else(this:@annotation.nullOut).addString(newStringBuilder(), start, sep, end).result()
13191321

13201322
/** Displays all elements of this $coll in a string using a separator string.
13211323
*
@@ -1328,7 +1330,8 @@ trait IterableOnceOps[+A, +CC[_], +C] extends Any { this: IterableOnce[A] =>
13281330
*
13291331
*@example `List(1, 2, 3).mkString("|") = "1|2|3"`
13301332
*/
1331-
@inlinefinaldefmkString(sep:String):String= mkString("", sep,"")
1333+
@annotation.nullOut
1334+
@inlinefinaldefmkString(sep:String):String= (this:@annotation.nullOut).mkString("", sep,"")
13321335

13331336
/** Displays all elements of this $coll in a string.
13341337
*
@@ -1339,7 +1342,8 @@ trait IterableOnceOps[+A, +CC[_], +C] extends Any { this: IterableOnce[A] =>
13391342
* of all elements of this $coll follow each other without any
13401343
* separator string.
13411344
*/
1342-
@inlinefinaldefmkString:String= mkString("")
1345+
@annotation.nullOut
1346+
@inlinefinaldefmkString:String= (this:@annotation.nullOut).mkString("")
13431347

13441348
/** Appends all elements of this $coll to a string builder using start, end, and separator strings.
13451349
* The written text begins with the string `start` and ends with the string `end`.
@@ -1365,10 +1369,11 @@ trait IterableOnceOps[+A, +CC[_], +C] extends Any { this: IterableOnce[A] =>
13651369
*@paramend the ending string.
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*@return the string builder `b` to which elements were appended.
13671371
*/
1372+
@annotation.nullOut
13681373
defaddString(b:StringBuilder,start:String,sep:String,end:String): b.type= {
13691374
valjsb= b.underlying
13701375
if (start.length!=0) jsb.append(start)
1371-
valit= iterator
1376+
valit=(this:@annotation.nullOut).iterator
13721377
if (it.hasNext) {
13731378
jsb.append(it.next())
13741379
while (it.hasNext) {

‎src/library/scala/collection/LinearSeq.scala

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -176,9 +176,10 @@ trait LinearSeqOps[+A, +CC[X] <: LinearSeq[X], +C <: LinearSeq[A] with LinearSeq
176176
None
177177
}
178178

179+
@annotation.nullOut
179180
overridedeffoldLeft[B](z:B)(op: (B,A)=>B):B= {
180181
varacc= z
181-
varthese:LinearSeq[A]= coll
182+
varthese:LinearSeq[A]=(this:@annotation.nullOut).coll
182183
while (!these.isEmpty) {
183184
acc= op(acc, these.head)
184185
these= these.tail

‎src/library/scala/collection/immutable/LazyList.scala

Lines changed: 0 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -416,19 +416,6 @@ final class LazyList[+A] private (lazyState: AnyRef /* EmptyMarker.type | () =>
416416
}
417417
}
418418

419-
/** LazyList specialization of foldLeft which allows GC to collect along the
420-
* way.
421-
*
422-
*@tparamB The type of value being accumulated.
423-
*@paramz The initial value seeded into the function `op`.
424-
*@paramop The operation to perform on successive elements of the `LazyList`.
425-
*@return The accumulated value from successive applications of `op`.
426-
*/
427-
@tailrec
428-
overridedeffoldLeft[B](z:B)(op: (B,A)=>B):B=
429-
if (isEmpty) z
430-
else tail.foldLeft(op(z, head))(op)
431-
432419
// LazyList.Empty doesn't use the SerializationProxy
433420
protected[this]defwriteReplace():AnyRef=
434421
if (knownNonEmpty)newSerializationProxy[A](this)elsethis

‎test/junit/scala/collection/immutable/LazyListGCTest.scala

Lines changed: 2 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -117,9 +117,8 @@ class LazyListGCTest {
117117
assertLazyListOpAllowsGC((ll, check)=> ll.tails.zipWithIndex.foreach {case (_, i)=> check(i) }, _=> ())
118118
}
119119

120-
@Test
120+
@Test@annotation.nowarn("cat=deprecation")
121121
deffoldLeft():Unit= {
122-
// fails when using `/:` instead of `foldLeft`
123-
assertLazyListOpAllowsGC((ll, check)=> ll.foldLeft(0){case (s, x)=> check(x); s+ x}, _=> ())
122+
assertLazyListOpAllowsGC((ll, check)=> ll./:(0){case (s, x)=> check(x); s+ x}, _=> ())
124123
}
125124
}

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