A dictionary that keeps track of the order that elements were added to it

OrderedDictionary

@interface OrderedDictionary : NSObject <NSCopying, NSCoding>{
    NSMutableDictionary *_dictionary;
    NSMutableArray *_array;
}

@property (readonly) NSUInteger count;

- (id)init;
- (id)initWithCapacity:(NSUInteger)capacity;
+ (id)dictionary;
+ (id)dictionaryWithCapacity:(NSUInteger)capacity;

- (void)setObject:(id)object forKeyedSubscript:(id<NSCopying>)aKey;

- (id)objectForKeyedSubscript:(id)key;
- (id)objectAtIndexedSubscript:(NSUInteger)idx;

- (void)removeObjectForKey:(id)aKey;
- (void)removeAllObjects;

- (NSArray *)allKeys;
- (NSArray *)allValues;

- (void)enumerateKeysAndObjectsUsingBlock:(void (^)(id key, id obj, BOOL *stop))block;
- (void)enumerateKeysUsingBlock:(void (^)(id key, NSUInteger idx, BOOL *stop))block;
- (void)enumerateObjectsUsingBlock:(void (^)(id obj, NSUInteger idx, BOOL *stop))block;

- (BOOL)isEqualToOrderedDictionary:(OrderedDictionary *)orderedDictionary;

@end

//
//  OrderedDictionary.m
//  OrderedDictionary
//
//  Created by Ayal Spitz on 3/25/13.
//  Copyright (c) 2013 Ayal Spitz. All rights reserved.
//

#import "OrderedDictionary.h"

@implementation OrderedDictionary

- (id)init{
    self = [super init];
    if (self) {
        _dictionary = [NSMutableDictionary dictionary];
        _array = [NSMutableArray array];
    }
    return self;
}

- (id)initWithCapacity:(NSUInteger)capacity{
    self = [super init];
    if (self) {
        _dictionary = [NSMutableDictionary dictionaryWithCapacity:capacity];
        _array = [NSMutableArray arrayWithCapacity:capacity];
    }
    return self;
}

#pragma mark -

+ (id)dictionary{
    return [[OrderedDictionary alloc]init];
}

+ (id)dictionaryWithCapacity:(NSUInteger)capacity{
    return [[OrderedDictionary alloc]initWithCapacity:capacity];
}

#pragma mark - NSCopying methods

- (id)copyWithZone:(NSZone *)zone{
    OrderedDictionary *dictionary = [[OrderedDictionary alloc]initWithCapacity:self.count];

    dictionary->_dictionary = [self->_dictionary mutableCopyWithZone:zone];
    dictionary->_array = [self->_array mutableCopyWithZone:zone];

    return dictionary;
}

#pragma mark - NSCoding methods

#define kDictionaryKey  @"Dictionary"
#define kArrayKey       @"Array"

- (id)initWithCoder:(NSCoder *)decoder{
    self = [super init];
    if (self) {
        _dictionary = [decoder decodeObjectForKey:kDictionaryKey];
        _array = [decoder decodeObjectForKey:kArrayKey];
    }
    return self;
}

- (void)encodeWithCoder:(NSCoder *)encoder{
    [encoder encodeObject:_dictionary forKey:kDictionaryKey];
    [encoder encodeObject:_array forKey:kArrayKey];
}

#pragma mark - Set methods

- (void)setObject:(id)object forKeyedSubscript:(id<NSCopying>)aKey{
    id value = _dictionary[aKey];
    if (object != nil){
        // if value isn't nil that means we are changing a key/value so we're changing it's index
        if (value != nil){
            [_array removeObject:aKey];
        }
        [_array addObject:aKey];
        _dictionary[aKey] = object;
    } else {
        [_array removeObject:aKey];
        [_dictionary removeObjectForKey:aKey];
    }
}

#pragma mark - Get Methods

- (id)objectForKeyedSubscript:(id)key{
    return _dictionary[key];
}

- (id)objectAtIndexedSubscript:(NSUInteger)idx{
    return self[_array[idx]];
}

#pragma mark - Remove Methods

- (void)removeObjectForKey:(id)aKey{
    self[aKey] = nil;
}

- (void)removeAllObjects{
    [_dictionary removeAllObjects];
    [_array removeAllObjects];
}

#pragma mark -

- (NSUInteger)count{
    return _dictionary.count;
}

#pragma mark - Keys and Objects methods

- (NSArray *)allKeys{
    return [_array copy];
}

- (NSArray *)allValues{
    NSMutableArray *objects = [NSMutableArray arrayWithCapacity:_array.count];
    
    [_array enumerateObjectsUsingBlock:^(id key, NSUInteger idx, BOOL *stop) {
        [objects addObject:self[key]];
    }];
    
    return objects;
}

- (void)enumerateKeysAndObjectsUsingBlock:(void (^)(id key, id obj, BOOL *stop))block{
    [_array enumerateObjectsUsingBlock:^(id key, NSUInteger idx, BOOL *stop) {
        id obj = self[key];
        block(key, obj, stop);
    }];
}

- (void)enumerateKeysUsingBlock:(void (^)(id key, NSUInteger idx, BOOL *stop))block{
    [_array enumerateObjectsUsingBlock:^(id key, NSUInteger idx, BOOL *stop) {
        block(key, idx, stop);
    }];
}

- (void)enumerateObjectsUsingBlock:(void (^)(id obj, NSUInteger idx, BOOL *stop))block{
    [_array enumerateObjectsUsingBlock:^(id key, NSUInteger idx, BOOL *stop) {
        id obj = self[key];
        block(obj, idx, stop);
    }];
}

#pragma mark - Equality methods
- (BOOL)isEqualToOrderedDictionary:(OrderedDictionary *)orderedDictionary{
    return ([self.allKeys isEqualToArray:orderedDictionary.allKeys] && [self.allValues isEqualToArray:orderedDictionary.allValues]);
}

@end