Question

I have the following problem, because i just have started coding objective-c.

I have some instance with

@interface MyClass
    @property (strong) MySecondClass *first;
    @property (strong) MySecondClass *second;
@end

@implementation MyClass
    @synthesize first = _first;
    @synthesize second = _second;

    /*this is called while initialisation*/
    -(void) initialisation{
        _first = [[MySecondClass alloc] init];
        _second = [[MySecondClass alloc] init];
     }

    /*what i want to do*/
    -(void) swap{
        // second one should be replaced with first one
        _second = _first; 

        // first pointer should be replaced by new instance
        _first = [[MySecondClass alloc] init];
    }

@end

Problem is, that when i call the swap method, the _first still points to the old object so _second will be replaced by same new object.

I already tried copy like follows, but it throws an exception.

 _second = [_first copy];

PS: Im using ARC

Edit

What i really would like to accomplish, would be something like:

 _second = _first
 MySecondClass *tmp = [[MySecondClass alloc] init];
 _first = &tmp;

But this shows compiler error: Implicit conversion of an indirect pointer to an Objective-C pointer to ‘MySecondClass *’ is disallowed with ARC

Thanks in advance.

Answer 1

What i really would like to accomplish, would be something like:

_second = _first
MySecondClass *tmp = [[MySecondClass alloc] init];
_first = &tmp;

But this shows compiler error: Implicit conversion of an indirect pointer to an Objective-C pointer to ‘MySecondClass *’ is disallowed with ARC

That’s because the values of _first, _second, and tmp are already pointers, so “&tmp” is a pointer to a pointer—an “indirect pointer” (not especially clear wording on the compiler authors’ part).

The solution there is to not say &tmp. You just want tmp here.