ios - __strong qualifier used in non ARC project -

the project non-arc enabled, (mistakingly) using arc compliant code libraries - 1 create singleton objects defined in gcdsingleton.h:

#define define_shared_instance + (id)sharedinstance {   static dispatch_once_t pred = 0;   __strong static id _sharedobject = nil;   dispatch_once(&pred, ^{     _sharedobject = ^{return [[self alloc] init];}();   });   return _sharedobject; } 

this seems work though shared object defined __strong qualifier. i'm wondering why doesn't cause error or @ least warning (latest xcode 4.6 , ios 6 sdk). also, since project not arc enabled, __strong qualifier doing, if anything?

in mrc code, __strong ignored.

i tried compile simple example

#import <foundation/foundation.h>  int main(int argc, char const *argv[]) {     __strong nsstring * foo = [[nsstring alloc] initwithformat:@"hello, %s", argv[1]];     nslog(@"%@", foo); } 

with arc

clang -fobjc-arc test.m -s -emit-llvm -o arc.ir 

and without arc

clang -fno-objc-arc test.m -s -emit-llvm -o mrc.ir 

and diff llvm ir output.

here's result of diff mrc.ir arc.ir

54a55,56 >   %17 = bitcast %0** %foo i8** >   call void @objc_storestrong(i8** %17, i8* null) nounwind 63a66,67 > declare void @objc_storestrong(i8**, i8*) >  

so difference between arc , mrc addition of objc_storestrong call.

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by way same code without __strong qualifier produce same exact results, since __strong default qualifier variables in arc.