CODEWITHSUNDEEP
iosobjective-c
Dhruv Jindal
Dhruv Jindal

Reputation: 1066

Programming concept regarding objective-c

I have a confusion regarding programming. What difference does it make in terms of memory if we do this in objective-c:

+(NSString *)getName {
  NSString *name = @"Hello";
  return name;
}

OR

+(NSString *)getName {
  return @"Hello";
}

Is both same or is there any difference in terms of speed and performance?

Upvotes: 1

Views: 92

Answers (1)

DarkDust
DarkDust

Reputation: 92306

The compiler will optimize the first example into the second example since the variable isn't used for anything else. So they are equivalent: none is faster, none saves any memory.

Edit:

So, I actually tried it and compared the assembler output.

Code used:

@implementation Test

- (NSString *)test1 {
        NSString *variable = @"Hello1";
        return variable;
}

- (NSString *)test2 {
        return @"Hello2";
}

@end

Compiler used:

Apple LLVM version 5.0 (clang-500.2.79) (based on LLVM 3.3svn) Target: x86_64-apple-darwin13.0.0

With no optimization (-O0), test1 does indeed have code for the unused variable (movq %rax, -24(%rbp) and movq -24(%rbp), %rax, so one additional memory write and read). But already at -O1 the variable is optimized away (as are the reads for the internal self and _cmd variables).

So in other words: with -O0 (no optimization), test1 is indeed slower than test2. But if optimizations are switched on, they are equivalent and result in the same code.

Upvotes: 8

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