On Jul 31, 2013, at 12:28 PM, Vincent Habchi <vi...@macports.org> wrote:
> David Duncan wrote:
>> Why would there be? Your just asking for a mutable copy of an empty string.
>> It should be equivalent to [[NSMutableString alloc] initWithString:@« »]
>
> But much slower I expect, since it creates a NSString, takes a mutable copy,
> then implicitly releases the constant empty NSString.
For giggles I tried some NSMutableString allocation patterns into my
microbenchmark test harness.
Simple alloc/init is the fastest:
100 [[[NSMutableString alloc] init] release]
102 [[NSMutableString new] release]
109 [NSMutableString string] // ARC enabled
117 [[@"" mutableCopy] release]
119 @autoreleasepool { [NSMutableString string]; } // ARC disabled
129 [[[NSMutableString alloc] initWithString:@""] release]
(Smaller numbers are better. Numbers are getrusage(RUSAGE_SELF) time for
10000000 iterations, normalized to fastest=100. Your mileage may vary.)
ARC and non-ARC scores are the same within measurement noise, except for
[NSMutableString string] where ARC can optimize the autoreleased return value
so the test doesn't need to spin the autorelease pool. Note th
> BTW, what’s the difference between [[NSMutableString alloc] init] and
> [[NSMutableString alloc] initWithString:@“”]?
Semantically there's no difference: you get the same string with the same
retain count.
--
Greg Parker gpar...@apple.com Runtime Wrangler
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