ARC forbids Objective-C objects in structs or unions despite marking the file -fno-objc-arc

问题

ARC forbids Objective-C objects in structs or unions despite marking the file -fno-objc-arc? Why is this so?

I had the assumption that if you mark it -fno-objc-arc you don\'t have this restriction.

回答1:

If you got this message try __unsafe_unretained. It is only safe, if the objects in the struct are unretained. Example: If you use OpenFeint with ARC the Class OFBragDelegateStrings says this error in a struct.

typedef struct OFBragDelegateStrings
{
     NSString* prepopulatedText;
     NSString* originalMessage;
} OFBragDelegateStrings;

to

typedef struct OFBragDelegateStrings
{
     __unsafe_unretained NSString* prepopulatedText;
     __unsafe_unretained NSString* originalMessage;
} OFBragDelegateStrings;

回答2:

Rather than using a struct, you can create an Objective-C class to manage the data instead.

回答3:

That is because arc can't track objects in structs or unions (since they are at that point plain C pointers).

Even though you marked the file/class in question with -fno-objc-arc you might still pass an object controlled by arc to it as parameter, which would most likely result in a memory leak.

回答4:

Looks like this now works without errors, probably after this change.

i.e., You can put normal (strong) pointers to Objective-C objects in a C struct. It is managed by ARC e.g., it is unretained when the struct is destructed. Verified with:

$ clang --version Apple LLVM version 10.0.0 (clang-1000.11.45.2)

来源：https://stackoverflow.com/questions/8093099/arc-forbids-objective-c-objects-in-structs-or-unions-despite-marking-the-file-f