Question

The XCode analyzer tells me there is a problem at line 4 — return [originalError copy]; — but I don’t see it. Help me please?

- (NSError *)errorFromOriginalError:(NSError *)originalError error:(NSError *)secondError
{
    if (secondError == nil) {
        return [originalError copy];
    }
    // ...
}

The problem description is:

• Potential leak of an object allocated on line 203
  • Method returns an Objective-C object with a +1 retain count (owning reference)
  • Object returned to caller as an owning reference (single retain count transferred to caller)
  • Object allocated on line 203 is returned from a method whose name (‘errorFromOriginalError:error:’) does not contain ‘copy’ or otherwise starts with ‘new’ or ‘alloc’. This violates the naming convention rules given in the Memory Management Guide for Cocoa (object leaked)
• Potential null dereference. According to coding standards in ‘Creating and Returning NSError Objects’ the parameter ‘error’ may be null

The third issue seems to suggest I should either change the name or the behaviour of the method further. Any suggestions on that? The method is derived from the errorFromOriginalError:error: method described in Apple’s Core Data Validation document. Its purpose is to combine originalError and secondError so that secondError is a sub-error of originalError.

My addition tries to ensure that the method still works if there is no actual secondError. Since a new error object is created if secondError is not nil, I wanted to recreate that in the case displayed above by simply copying the error object.

Answer 1

You are making a copy of originalError, but your function name implies that the returned object will be autoreleased. Try

return [[originalError copy] autorelease];