Foundation data structures Cyril @notorca Lashkevich 

Agenda NSMutableDictionary/NSMutableSet/NSCountedSet CFMutableDictionary/CFMutableSet/CFBag NSMapTable/NSHashTable/NSPointerArray CFBitVector/CFTree 

NSMutableDictionary Key-value paris collection Key is copied < NSCopying > Implemented as hash-map (hash, isEqual:) enumerateKeysAndObjectsUsingBlock: is more optimal than keyEnumerator Not thread safe in contrast to NSDictionary 

Hash/isEqual: invariant [a isEqual:b] -> [a hash] == [b hash] return 42; is valid hash implementation return [self.a hash] ^ [self.b hash] ^ [self.c hash]; 

typedef id (^DictBlock)(id);
 DictBlock empty = ^id (id key) { return nil; };
 DictBlock add(DictBlock d, id key, id obj) {
 return ^id (id k) {
 return [k isEqual:key] ? obj : d(k);
 };
 } DictBlock d = empty; d = add(d, @(1), @"abc"); d = add(d, @"def", @(5)); NSLog(@"%@ : %@", @(1), d(@(1))); NSLog(@"%@ : %@", @"def", d(@"def")); NSLog(@"%@ : %@", @(42), d(@(42))); 1 : abc def : 5 42 : (null) 

NSMutableSet Unordered collection of distinct (hash/isEqual:) objects Objects should not change after adding to NSMutableSet Not thread safe in contrast to NSSet 

NSCountedSet Like NSMutableSet, but with counter associated with each object Mutable, but without word „mutable” in the class name Not thread safe 

CFMutableDictionary Toll-free bridge for NSMutableDictionary More flexible Sources are published Worst Expected Access O(n) O(1) Insert/ Delete O(n*n) O(1) 

Flexibility of CFMutableDictionary Full control of memory management, comparing and hashing CFMutableDictionaryRef CFDictionaryCreateMutable( CFAllocatorRef allocator, CFIndex capacity, const CFDictionaryKeyCallBacks *keyCallBacks, const CFDictionaryValueCallBacks *valueCallBacks ); 

CFMutableDictionary callbacks CFDictionaryRetainCallBack CFDictionaryReleaseCallBack CFDictionaryCopyDescriptionCallBack CFDictionaryEqualCallBack CFDictionaryHashCallBack 

CFMutableSet Toll-free bridge for NSMutableSet CFSetCallBacks similar to CFDictionaryValueCall
 Backs Not a toll-free bridge for NSCountedSet, but with same functionality CFBagCallbacks similar to CFSetCallBacks CFBag 

CFBasicHash Heart of hash tables implementation in CF CFBasicHash.c, common for Dictionary/Set/Bag Hash table size is a prime number Implements different rehashing modes for collisions (but Dictionary is using only Linear) CFBasicHash.h is private and not included into SDK 

NSMapTable/NSHashTable Same as NSMutableDictionary/NSMutableSet but there is possible to choose mode for storing keys and values: weak, copy, retain, unsafe_unretained From iOS 6.0 

NSPointerArray Similar to NSMutableArray but with full memory management control Has setCount: method Can store NULL Uses NSPointerFunctions 

NSCache NSMutableDictionary for caching Thread safe Does not copy keys Frees automaticaly 

CFBitVector/CFMutableBitVector Ordered collection of 0 and 1 Can be emulated with NSMutableArray of @(YES) and @(NO) or NSIndexSet 

CFTree Helper functions to create and manage hierarchical structures. For each node: one parent and multiple children Can be sorted A lot of boilerplate code to use 

Bonus. CFArray Not a simple wrapper for C array! Worst access time is O(log n) Internal structure can be changed when array size changes Implemented as deque of buckets 

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