Custom single KeyValuePair class vs NSMutableDictionary - objective-c

Question

I came into a situation where I had to write a loop with a good amount if iterations and in this loop I had a NSData object that I had to associate with a key. This lead me to search for a simple objective-c _KeyValuePair_ class but coulnt not find one so I wrote my own. Now I'm curious to see if there is any benefit over just using an NSMutableDictinoary holding just 1 key and value. After trying both throughout my project I can't tell much difference on the App UI side or with Instruments Time Profiler.
So my questions are:
Could a single kvpair class be more efficient than a NSMutableDictionary
Does a NSMutableDict allocate any larger amount of space by default then this does
Is there actually a standard single key value pair class that I just missed
Some code:
for (int i = 0, count = [photoUrls count]; i < count; ++i) {
// Example usage of the kvp class
NSMutableDictionary *imageRequest = [[NSMutableDictionary alloc] init];
JHKeyValuePair *kvPair = [[JHKeyValuePair alloc] initWithKey:#"DAILY" andValue:[NSNumber numberWithInt:i];
[imageRequest setObject:self forKey:#"delegate"];
[imageRequest setObject:kvPair forKey:#"userInfo"];
[kvPair release];
[imageRequest setObject:[dailySpecialData objectForKey:#"IMAGE_URL"] forKey:#"url"];
[imageDownloader addDownloadRequestToQueue:imageRequest];
[imageRequest release];
}
JHKeyValuePair.h
#interface JHKeyValuePair : NSObject {
id key;
id value;
}
#property (nonatomic, retain) id key;
#property (nonatomic, retain) id value;
- (id)initWithKey:(id)aKey andValue:(id)aValue;
#end
JHKeyValuePair.m
#import "JHKeyValuePair.h"
#implementation JHKeyValuePair
#synthesize key;
#synthesize value;
- (id)initWithKey:(id)aKey andValue:(id)aValue {
if ((self = [super init])) {
key = [aKey retain];
value = [aValue retain];
}
return self;
}
- (void)dealloc {
[key release], key = nil;
[value release], value = nil;
[super dealloc];
}
- (id)copyWithZone:(NSZone *)zone {
JHKeyValuePair *copy = [[JHKeyValuePair allocWithZone:zone] init];
[copy setKey:self.key];
[copy setValue:self.value];
return copy;
}
- (BOOL)isEqual:(id)anObject {
BOOL ret;
if (self == anObject) {
ret = YES;
} else if (![anObject isKindOfClass:[JHKeyValuePair class]]) {
ret = NO;
} else {
ret = [key isEqual:((JHKeyValuePair *)anObject).key] && [value isEqual:((JHKeyValuePair *)anObject).value];
}
return ret;
}
#end
Edit to fix the initial explanation. Seems I got sidetracked mid-sentance and never came back to finish it.

Answer 1

If you really want to get speed you are doing a lot of unnecessary retain releases that probably aren't necessary every time you set your key/values. If you use a struct and some basic c code you can achieve something a little quicker but you sacrifice the simple and consistent memory management you get from doing it the objective c way.
typedef struct {
id key;
id value;
} Pair;
BOOL isEqual(Pair a, Pair b); //...
// You will need to clean up after yourself though:
void PairRelease(Pair p) {
[p.key release];
[p.value release];
}