On 7 Mar 2014, at 6:54 AM, Bill Cheeseman <[email protected]> wrote:
> My code calls -[NSArray objectAtIndex:]. I compile it with Xcode 5.0.2 on OS
> X 10.9.x Mavericks in a project with the target's Base SDK set to 10.9 and
> the OS X Deployment Target set to OS X 10.7. It works fine when I run it on
> OS X 10.9 or OS X 10.8.
>
> However, when I run it on Mac OS X 10.7 Lion, I get a runtime error claiming
> it encountered an invalid argument, namely, the unrecognized selector
> -objectAtIndexedSubscript:. The NSArray Class Reference notes that
> -objectAtIndexedSubscript: is available only in OS X 10.8 and later, and that
> it is "identical to objectAtIndex:". Of course, -objectAtIndex: still exists
> in the 10.9 API, and it is not marked as deprecated.
>
> It appears, therefore, that the compiler generated a call to
> -objectAtIndexedSubscript: even though my source specifies -objectAtIndex:
> and a deployment version of 10.7.
I tried a Foundation command-line tool, 10.9 SDK, 10.7 deployment:
int main(int argc, const char * argv[])
{
@autoreleasepool {
NSArray * myArray = @[ @"alpha",
@"beta",
@"gamma",
@"delta"
];
NSString * zerothString = [myArray objectAtIndex: 0];
NSLog(@"The string is %@", zerothString);
}
return 0;
}
Note that I’m using an array literal, which is backwards-compatible, and you’d
think that might tempt the compiler to emit objectAtIndexedSubscript:.
My disassembly of main.o (Hopper Disassembler, UI a bit odd, but very valuable)
shows no reference to objectAtIndexedSubscript:, so it’s not the compiler.
There is a reference to _objc_msgSend_fixup, which you’d expect to be generic.
The runtime _might_ special-case objectAtIndex: as an alias for
objectAtIndexedSubscript:, but that’s a runtime issue, not compile-time. I saw
nothing in the public source of the runtime, but I didn’t put much effort into
it.
And wasn’t the indexed-subscript notation supported in ObjC in late 10.7.x? And
I seem to remember that objectAtIndexedSubscript: was implemented then (and
retroactively supported as “public” API in 10.7 MAS submissions). I may be
wrong about the chronology.
See the Assembly assistant while your code is in the main editor.
This is all bloviation on what Jens said: Check the backtrace.
— F
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