From a79c69a5f1b357e73a4c628402a71856e87895df Mon Sep 17 00:00:00 2001
From: Adlai Holler <guy.on.internet@me.com>
Date: Sun, 24 Jul 2016 15:31:09 -0700
Subject: [PATCH] [ASWeakSet] Refactor to use NSHashTable (#1976)

[ASWeakSet] Tweak it

[ASWeakSet] Simplify
---
 AsyncDisplayKit/Private/ASWeakSet.h |  5 ++--
 AsyncDisplayKit/Private/ASWeakSet.m | 42 ++++++++++-------------------
 2 files changed, 16 insertions(+), 31 deletions(-)

diff --git a/AsyncDisplayKit/Private/ASWeakSet.h b/AsyncDisplayKit/Private/ASWeakSet.h
index e44e68a1a5..9a8707eb84 100644
--- a/AsyncDisplayKit/Private/ASWeakSet.h
+++ b/AsyncDisplayKit/Private/ASWeakSet.h
@@ -35,10 +35,9 @@ NS_ASSUME_NONNULL_BEGIN
 - (NSArray *)allObjects;
 
 /**
- How many objects are contained in this set.
+ * How many objects are contained in this set.
  
- NOTE: This method is O(N). Consider using the `empty`
- property.
+ * NOTE: This computed property is O(N). Consider using the `empty` property.
  */
 @property (nonatomic, readonly) NSUInteger count;
 
diff --git a/AsyncDisplayKit/Private/ASWeakSet.m b/AsyncDisplayKit/Private/ASWeakSet.m
index 773af682fd..c68b730db9 100644
--- a/AsyncDisplayKit/Private/ASWeakSet.m
+++ b/AsyncDisplayKit/Private/ASWeakSet.m
@@ -13,7 +13,7 @@
 #import "ASWeakSet.h"
 
 @interface ASWeakSet<__covariant ObjectType> ()
-@property (nonatomic, strong, readonly) NSMapTable<ObjectType, NSNull *> *mapTable;
+@property (nonatomic, strong, readonly) NSHashTable<ObjectType> *hashTable;
 @end
 
 @implementation ASWeakSet
@@ -22,59 +22,45 @@
 {
   self = [super init];
   if (self) {
-    _mapTable = [NSMapTable weakToStrongObjectsMapTable];
+    _hashTable = [NSHashTable weakObjectsHashTable];
   }
   return self;
 }
 
 - (void)addObject:(id)object
 {
-  [_mapTable setObject:(NSNull *)kCFNull forKey:object];
+  [_hashTable addObject:object];
 }
 
 - (void)removeObject:(id)object
 {
-  [_mapTable removeObjectForKey:object];
+  [_hashTable removeObject:object];
 }
 
 - (void)removeAllObjects
 {
-  [_mapTable removeAllObjects];
+  [_hashTable removeAllObjects];
 }
 
 - (NSArray *)allObjects
 {
-  // We use keys instead of values in the map table for efficiency and better characteristics when the keys are deallocated.
-  // Documentation is currently unclear on whether -keyEnumerator retains its values, but does imply that modifying a
-  // mutable collection is still not safe while enumerating that way - which is one of the main uses for this method.
-  // A helper function called NSAllMapTableKeys() might do exactly what we want and should be more efficient, but unfortunately
-  // is throwing a strange compiler error and may not be available in practice on the latest iOS version.
-  // Lastly, even -dictionaryRepresentation and then -allKeys won't work, because it attempts to copy the values of each key,
-  // which may not support copying (such as ASRangeControllers).
-  NSMutableArray *allObjects = [NSMutableArray array];
-  for (id object in _mapTable) {
-    [allObjects addObject:object];
-  }
-  return allObjects;
+  return _hashTable.allObjects;
 }
 
 - (BOOL)containsObject:(id)object
 {
-  return [_mapTable objectForKey:object] != nil;
+  return [_hashTable containsObject:object];
 }
 
 - (BOOL)isEmpty
 {
-  for (__unused id object in _mapTable) {
-    return NO;
-  }
-  return YES;
+  return [_hashTable anyObject] == nil;
 }
 
 /**
- Note: The `count` property of NSMapTable is unreliable
- in the case of weak-to-strong map tables because entries
- whose keys have been deallocated are not removed immediately.
+ Note: The `count` property of NSHashTable is unreliable
+ in the case of weak-object hash tables because entries
+ that have been deallocated are not removed immediately.
  
  In order to get the true count we have to fall back to using
  fast enumeration.
@@ -82,7 +68,7 @@
 - (NSUInteger)count
 {
   NSUInteger count = 0;
-  for (__unused id object in _mapTable) {
+  for (__unused id object in _hashTable) {
     count += 1;
   }
   return count;
@@ -90,12 +76,12 @@
 
 - (NSUInteger)countByEnumeratingWithState:(NSFastEnumerationState *)state objects:(__unsafe_unretained id  _Nonnull *)buffer count:(NSUInteger)len
 {
-  return [_mapTable countByEnumeratingWithState:state objects:buffer count:len];
+  return [_hashTable countByEnumeratingWithState:state objects:buffer count:len];
 }
 
 - (NSString *)description
 {
-  return [[super description] stringByAppendingFormat:@" count: %lu, contents: %@", (unsigned long)self.count, _mapTable];
+  return [[super description] stringByAppendingFormat:@" count: %tu, contents: %@", self.count, _hashTable];
 }
 
 @end