Automatic Reference Counting: Pointer to non-const type 'NSError *' with no explicit ownership

In updating some of my code to be in compatible with the iOS 5 SDK, I attempted to refactor my code by using "Convert to Objective-C ARC" in Xcode and received an error. The error occurs on an instance variable in my .h file.

NSError **_error;

The error says "Pointer to non-const type 'NSError *' with no explicit ownership." How might I fix this?

Answers


When storing NSError objects in an instance variable you have to declare it as a simple pointer:

@interface Foo : NSObject
{
    NSError *_errror;
}

NSError ** is only used to indirectly return NSError objects from a method to the caller. It is (probably) an error to store it in an instance variable.


You can use one of the lifetime qualifiers described in the Transitioning to ARC Release Notes

For NSError ** you'd use __autoreleasing so the example provided by Nikolai would then look like this

@interface Foo : NSObject
{
    NSError * __autoreleasing *error;
}

The syntax is a little weird and you should follow Nikolais advice, but if you're sure NSError ** is what you want this should work.


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