Property vs. ivar in times of ARC

Question

It is my understanding that setting an ivar now retains the object being assigned to it, since setting variables defaults to the strong qualifier. Because ivars are in the scope of the object they are declared in and strong retains objects within the scope of the variable, this means the ivars value would never be released while the object containing the ivar is still alive.

Is this correct?

If so, am I right in thinking that there is, in terms of memory management, no difference between a retaining (strong) property and a simple ivar anymore?

Answer 1

If a variable:

1. Is declared in a class using ARC.
2. Is used solely for class implementation (not exposed as part of the class interface).
3. Does not require any KVO.
4. Does not require any custom getter/setter.

Then it is appropriate to declare it as an ivar without a corresponding @property/@synthesize, and to refer to it directly within the implementation. It is inline with Encapsulation to declare this ivar in the class implementation file.

// MyClass.h
@interface MyClass : ParentClass
@end

// MyClass.m
@implementation MyClass {
    NSString *myString;
}

- (void)myMethod {
    myString = @"I'm setting my ivar directly";
}
@end

• This ivar will be treated as __strong by the ARC compiler.
• It will be initialized to nil if it is an object, or 0 if it is a primitive.

Answer 2

You can't use KVO and do custom getter and setters with instance variables other than that they are very similar when using ARC.