Question

I’m reading a project code from others, it could be compiled successfully in 32bit, but when I switch the project to 64bit, there is one error message just like the title said.

code:

[obj setAction:(SEL)@selector(start:)];

I know the return value type of @selector is SEL and the parameter of setAction needs a SEL args, but why it failed in 64bit? What’s the SEL type actually?

Thanks!

Answer 1

It should not fail, but you don’t need the cast at all. @selector() expressions are already of type SEL. Just write

[obj setAction:@selector(start:)];

The SEL type is, in terms of C, struct objc_selector *. On OS X and iOS, it is, however? backed by a plain const char *, which is unified by the linker and the kernel during loading time.