[swift-corelibs-dev] [swift-evolution] Proposal: add `noescape` attribute to public API (particularly libdispatch)

[Philippe Hausler]

To re-iterate my comment on github; I think this is a great idea. 

There are a couple of suggestions for scope limiting; since this will require changes in the c and objective-c layers to support this attribute it would be good to limit this for now to just the core libraries (dispatch, XCTest and Foundation). 

Most likely future optimizations in c and objective c code can be applied in addition to the positive effect to swift code.

> On Dec 8, 2015, at 12:02 AM, Jacob Bandes-Storch via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Alright, I've written up a proposal: https://github.com/apple/swift-evolution/pull/40 <https://github.com/apple/swift-evolution/pull/40>
> 
> Feedback welcome!
> 
> Jacob
> 
> On Sat, Dec 5, 2015 at 2:25 PM, Jacob Bandes-Storch <jtbandes at gmail.com <mailto:jtbandes at gmail.com>> wrote:
> On Sat, Dec 5, 2015 at 1:40 PM, Tony Parker <anthony.parker at apple.com <mailto:anthony.parker at apple.com>> wrote:
> One topic I wanted to discuss was finding a comprehensive list of API that needs the attribute.
> 
> On this subject, here are some other APIs which could use the annotation. Again, I think these should be annotated even in the C/Objective-C headers, so they can benefit C/Objective-C callers as well.
> 
> - bsearch, heapsort, qsort, mergesort, psort, and their _b variants
> 
> "passing test" methods:
> - -[{NSArray,NSOrderedSet} indexOfObjectPassingTest:]
> - -[{NSArray,NSOrderedSet} indexesOfObjectsPassingTest:]
> - -[{NSArray,NSOrderedSet} indexOfObjectsAtIndexes:passingTest:]
> - -[{NSArray,NSOrderedSet} indexesOfObjectsAtIndexes:passingTest:]
> - -[SCNNode childNodesPassingTest:]
> - -[SCNSceneSource entriesPassingTest:]
> - -[AVAudioUnitComponentManager componentsPassingTest:]
> - -[NSIndexSet indexPassingTest:]
> - -[NSIndexSet indexWithOptions:passingTest:]
> - -[NSIndexSet indexesPassingTest:]
> - -[NSIndexSet indexesWithOptions:passingTest:]
> - -[NSIndexSet indexInRange:options:passingTest:]
> - -[NSIndexSet indexesInRange:options:passingTest:]
> - -[NSSet objectsPassingTest:]
> - -[NSSet objectsWithOptions:passingTest:]
> - -[NSDictionary keysOfEntriesPassingTest:]
> - -[NSDictionary keysOfEntriesWithOptions:passingTest:]
> 
> "using comparator" methods:
> - -[NSArray indexOfObject:inSortedRange:options:usingComparator:]
> - -[NSArray sortedArrayUsingComparator:]
> - -[NSArray sortedArrayWithOptions:usingComparator:]
> - -[NSDictionary keysSortedByValueUsingComparator:]
> - -[NSDictionary keysSortedByValueWithOptions:usingComparator:]
> - -[NSMutableArray sortUsingComparator:]
> - -[NSMutableArray sortWithOptions:usingComparator:]
> - -[NSMutableOrderedSet sortWithOptions:usingComparator:]
> - -[NSMutableOrderedSet sortRange:options:usingComparator:]
> 
>  (and some of these have "usingFunction" variants)
> 
> "enumerate using block" methods:
> - -[NSTableView enumerateAvailableRowViewsUsingBlock:]
> - -[SKPhysicsWorld enumerateBodiesAtPoint:usingBlock:]
> - -[SKPhysicsWorld enumerateBodiesInRect:usingBlock:]
> - -[NSData enumerateByteRangesUsingBlock:]
> - -[SCNNode enumerateChildNodesUsingBlock:]
> - -[SCNNode enumerateChildNodesWithName:usingBlock:]
> - -[NSIndexSet enumerateIndexesUsingBlock:]
> - -[NSIndexSet enumerateIndexesWithOptions:usingBlock:]
> - -[NSDictionary enumerateKeysAndObjectsUsingBlock:]
> - -[NSDictionary enumerateKeysAndObjectsWithOptions:usingBlock:]
> - -[NSString enumerateLinesUsingBlock:]
> - -[NSString enumerateSubstringsInRange:options:usingBlock:]
> - -[{NSArray,NSSet,NSOrderedSet} enumerateObjectsUsingBlock:]
> - -[{NSArray,NSSet,NSOrderedSet} enumerateObjectsWithOptions:usingBlock:]
> - -[NSIndexSet enumerateRangesUsingBlock:]
> - -[NSIndexSet enumerateRangesWithOptions:usingBlock:]
> - -[NSIndexSet enumerateRangesInRange:options:usingBlock:]
> - -[MPMediaEntity enumerateValuesForProperties:usingBlock:]
> - -[NSMetadataQuery enumerateResultsUsingBlock:]
> - -[NSMetadataQuery enumerateResultsWithOptions:usingBlock:]
> 
> misc:
> - -[NSDocument performSynchronousFileAccessUsingBlock:]
> 
> Wow, that's more than I expected to find! This is obviously beyond the scope of just libdispatch, and I think a lot of these should probably change upstream, in their original frameworks, internally (not something that community members can really contribute to).
> 
> Arguably, the "enumerateXUsingBlock:" pattern should be bridged to Swift as something SequenceType-ish which can be `for-in`ed.
> 
> Jacob Bandes-Storch
> 
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