(take 2) SR-0140: Bridge Optionals to nonnull ObjC objects by bridging their payload, or using a sentinel. #4869
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| Original file line number | Diff line number | Diff line change |
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@@ -487,3 +487,81 @@ extension Optional { | |
| } | ||
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| } | ||
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| //===----------------------------------------------------------------------===// | ||
| // Bridging | ||
| //===----------------------------------------------------------------------===// | ||
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| #if _runtime(_ObjC) | ||
| extension Optional : _ObjectiveCBridgeable { | ||
| // The object that represents `none` for an Optional of this type. | ||
| internal static var _nilSentinel : AnyObject { | ||
| @_silgen_name("_swift_Foundation_getOptionalNilSentinelObject") | ||
| get | ||
| } | ||
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| public func _bridgeToObjectiveC() -> AnyObject { | ||
| // Bridge a wrapped value by unwrapping. | ||
| if let value = self { | ||
| return _bridgeAnythingToObjectiveC(value) | ||
| } | ||
| // Bridge nil using a sentinel. | ||
| return type(of: self)._nilSentinel | ||
| } | ||
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| public static func _forceBridgeFromObjectiveC( | ||
| _ source: AnyObject, | ||
| result: inout Optional<Wrapped>? | ||
| ) { | ||
| // Map the nil sentinel back to .none. | ||
| // NB that the signature of _forceBridgeFromObjectiveC adds another level | ||
| // of optionality, so we need to wrap the immediate result of the conversion | ||
| // in `.some`. | ||
| if source === _nilSentinel { | ||
|
There was a problem hiding this comment. Are all NSNulls guaranteed to be identical? There was a problem hiding this comment. It is documented as a singleton, but I would double-check with someone from Foundation. @phausler? There was a problem hiding this comment. There's example ObjC code that uses There was a problem hiding this comment. NSNull in Darwin is a singleton (swift-corelibs-foundation it cannot be since we don't have factory patterns) |
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| result = .some(.none) | ||
| return | ||
| } | ||
| // Otherwise, force-bridge the underlying value. | ||
| let unwrappedResult = source as! Wrapped | ||
| result = .some(.some(unwrappedResult)) | ||
| } | ||
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| public static func _conditionallyBridgeFromObjectiveC( | ||
| _ source: AnyObject, | ||
| result: inout Optional<Wrapped>? | ||
| ) -> Bool { | ||
| // Map the nil sentinel back to .none. | ||
| // NB that the signature of _forceBridgeFromObjectiveC adds another level | ||
| // of optionality, so we need to wrap the immediate result of the conversion | ||
| // in `.some` to indicate success of the bridging operation, with a nil | ||
| // result. | ||
| if source === _nilSentinel { | ||
| result = .some(.none) | ||
| return true | ||
| } | ||
| // Otherwise, try to bridge the underlying value. | ||
| if let unwrappedResult = source as? Wrapped { | ||
| result = .some(.some(unwrappedResult)) | ||
| return true | ||
| } else { | ||
| result = .none | ||
| return false | ||
| } | ||
| } | ||
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| public static func _unconditionallyBridgeFromObjectiveC(_ source: AnyObject?) | ||
| -> Optional<Wrapped> { | ||
| if let nonnullSource = source { | ||
| // Map the nil sentinel back to none. | ||
| if nonnullSource === _nilSentinel { | ||
| return .none | ||
| } else { | ||
| return .some(nonnullSource as! Wrapped) | ||
| } | ||
| } else { | ||
| // If we unexpectedly got nil, just map it to `none` too. | ||
| return .none | ||
| } | ||
| } | ||
| } | ||
| #endif | ||
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,99 @@ | ||
| //===----------------------------------------------------------------------===// | ||
| // | ||
| // This source file is part of the Swift.org open source project | ||
| // | ||
| // Copyright (c) 2014 - 2016 Apple Inc. and the Swift project authors | ||
| // Licensed under Apache License v2.0 with Runtime Library Exception | ||
| // | ||
| // See http://swift.org/LICENSE.txt for license information | ||
| // See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors | ||
| // | ||
| //===----------------------------------------------------------------------===// | ||
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| #include "swift/Basic/Lazy.h" | ||
| #include "swift/Basic/LLVM.h" | ||
| #include "swift/Runtime/Metadata.h" | ||
| #include "swift/Runtime/Mutex.h" | ||
| #include "swift/Runtime/ObjCBridge.h" | ||
| #include <vector> | ||
| #import <Foundation/Foundation.h> | ||
| #import <CoreFoundation/CoreFoundation.h> | ||
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| using namespace swift; | ||
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| /// Class of sentinel objects used to represent the `nil` value of nested | ||
| /// optionals. | ||
| @interface _SwiftNull : NSObject { | ||
|
There was a problem hiding this comment. this should'd probably be There was a problem hiding this comment. Good idea. We aren't making any of the runtime-private classes hidden yet. I think we should do that as a separate patch, though, just to keep the risk of unintentional breakage minimal for this as a 3.0.1 patch. |
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| @public | ||
| unsigned depth; | ||
| } | ||
| @end | ||
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| @implementation _SwiftNull : NSObject | ||
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| - (NSString*)description { | ||
| return [NSString stringWithFormat:@"<%@ %p depth = %u>", [self class], | ||
| self, | ||
| self->depth]; | ||
| } | ||
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| @end | ||
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| namespace { | ||
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| struct SwiftNullSentinelCache { | ||
| std::vector<id> Cache; | ||
| StaticReadWriteLock Lock; | ||
| }; | ||
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| static Lazy<SwiftNullSentinelCache> Sentinels; | ||
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| static id getSentinelForDepth(unsigned depth) { | ||
| // For unnested optionals, use NSNull. | ||
| if (depth == 1) | ||
| return (id)kCFNull; | ||
| // Otherwise, make up our own sentinel. | ||
| // See if we created one for this depth. | ||
| auto &theSentinels = Sentinels.get(); | ||
| unsigned depthIndex = depth - 2; | ||
| { | ||
| StaticScopedReadLock lock(theSentinels.Lock); | ||
| const auto &cache = theSentinels.Cache; | ||
| if (depthIndex < cache.size()) { | ||
| id cached = cache[depthIndex]; | ||
| if (cached) | ||
| return cached; | ||
| } | ||
| } | ||
| // Make one if we need to. | ||
| { | ||
| StaticScopedWriteLock lock(theSentinels.Lock); | ||
| if (depthIndex >= theSentinels.Cache.size()) | ||
| theSentinels.Cache.resize(depthIndex + 1); | ||
| auto &cached = theSentinels.Cache[depthIndex]; | ||
| // Make sure another writer didn't sneak in. | ||
| if (!cached) { | ||
| auto sentinel = [[_SwiftNull alloc] init]; | ||
| sentinel->depth = depth; | ||
| cached = sentinel; | ||
|
There was a problem hiding this comment. Am I not reading this correctly? On cache miss you are not storing a value into the cache? There was a problem hiding this comment.
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| } | ||
| return cached; | ||
| } | ||
| } | ||
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| } | ||
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| /// Return the sentinel object to use to represent `nil` for a given Optional | ||
| /// type. | ||
| SWIFT_RUNTIME_STDLIB_INTERFACE SWIFT_CC(swift) | ||
| extern "C" | ||
| id _swift_Foundation_getOptionalNilSentinelObject(const Metadata *Wrapped) { | ||
| // Figure out the depth of optionality we're working with. | ||
| unsigned depth = 1; | ||
| while (Wrapped->getKind() == MetadataKind::Optional) { | ||
| ++depth; | ||
| Wrapped = cast<EnumMetadata>(Wrapped)->getGenericArgs()[0]; | ||
| } | ||
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| return objc_retain(getSentinelForDepth(depth)); | ||
| } | ||
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Is this worth caching, for SIL optimization purposes?
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Unfortunately, we don't support stored static properties on generic types. We have to rely on the runtime's caching.