An issue about @property (nonatomic, copy)

Question

I am a fresh man in iPhone SDK development area. I write a interface Person and implement protocol
NSCopying and it can work properly. I write another interface MyTableViewController to inherit UITableViewController, and MyTableViewController has a property person, which is a declared as
@property (nonatomic, copy). The source code is something like follows:
//Person.h
@interface Person : NSObject<NSCopying>
//Person.m
- (id)copyWithZone:(NSZone *)zone
NSLog(@"copy");
//other code
@class Peson;
@interface MyTableViewController : UITableViewController
Person *person;
@property (nonatomic, copy) Person *person;
However, when I use following souce code,
Person *p2 = p1;
I can't see the log "copy" output. If I use
Person *p2 = [p1 copy];
I can see the log "copy".
Any one know what's the root cause of this issue. Thanks a lot.

Answer 1

laurent has half of it. The important point to remember is that you can't invoke a setter when you use direct assignment. For example, assuming p1 points to an instance of Person:
// this line just assigns the value of p1 to a second pointer, p2.
Person *p2 = p1;
// this would cause Person::copyWithZone to be invoked:
Peson *myPeson = [[Peson alloc] init];
myPeson.person = p1;
// the 2nd line above has exactly the same meaning as:
[myPeson setPerson:p1];
// assuming setPerson is @synthesized, copy is used because of the @property attribute