About 35 seconds after I posted this article, Lawrence Lomax pointed out that Mark Dalrymple had already published exhaustive details about NSString comparisons on the Big Nerd Ranch blog. Go read that and stop wasting your time over here!
Earlier tonight, I came across a snippet of Objective-C code where the author had used -compare: instead of -isEqualToString: in every instance. My general rule is to always use the highest-level, most readable API unless there is a critical performance
issue when doing so, so I was intrigued (although I was pretty sure why this was being done):
Here’s the simple test I ran:
NSString *someString = @"LANA!";
NSString *otherString = @"LAAANAA!";
NSString *sameString = @"LANA!";
NSTimeInterval start = [NSDate timeIntervalSinceReferenceDate];
BOOL boop = [someString isEqualToString:otherString];
NSLog(@"%f", [NSDate timeIntervalSinceReferenceDate] - start);
start = [NSDate timeIntervalSinceReferenceDate];
BOOL bleep = [someString compare:otherString] == NSOrderedSame;
NSLog(@"%f", [NSDate timeIntervalSinceReferenceDate] - start);
start = [NSDate timeIntervalSinceReferenceDate];
BOOL boopSame = [someString isEqualToString:sameString];
NSLog(@"%f", [NSDate timeIntervalSinceReferenceDate] - start);
start = [NSDate timeIntervalSinceReferenceDate];
BOOL bleepSame = [someString compare:sameString] == NSOrderedSame;
NSLog(@"%f", [NSDate timeIntervalSinceReferenceDate] - start);
| Method | Result | Time Logged (seconds) |
|---|---|---|
-isEqualToString: |
Strings did not match | 0.000014 |
-compare: |
Strings did not match | 0.000007 |
-isEqualToString: |
Strings matched | 0.000001 |
-compare: |
Strings matched | 0.000002 |
Turns out that -compare: is roughly twice as fast as -isEqualToString: when the strings don’t match and the inverse is true when the strings match — although with the matching strings the difference is very nearly negligible.
Personally, I’ll probably stick to -isEqualToString: unless performance is absolutely critical — I find it much more readable, and that’s almost always more important than saving 0.000007 seconds.