How can I make a deep copy in Objective-C?

Question

I\'m learning ios development and I\'m confused with deep copying in Objective-C. For example,I have three class below. Now I want to deep copy ClassA, can anybody teach me

Answer 1

Objective-C on iOS doesn’t offer any direct language or library construct to switch between a shallow and a deep copy. Each class defines what it means to “get its copy”:

@implementation ClassA

- (id) copyWithZone: (NSZone*) zone
{
    ClassA *copy = [super copyWithZone:zone];
    [copy setBClass:bClass]; // this would be a shallow copy
    [copy setBClass:[bClass copy]]; // this would be a deep copy
    return copy;
}

@end

Of course you would have to do the same decision in ClassB and ClassC. If I am not mistaken, the usual semantics for a copy in Objective-C is to return a shallow copy. See also this question about copying arrays for more discussion of the topic.