MRC的下setter访问器的两种形式

// Person复合了Phone和Room

// 第一种

- (void)setPhone:(Phone *)phone

{

if (phone != _phone)

{

[_phone release];

_phone = [phone retain];

}

}

// 第二种

- (void)setRoom:(Room *)room

{

[room retain];

[_room release];

_room = room;

}

- (void)dealloc

{

NSLog(@"%s", __func__);

self.phone = nil; // 赋值为nil会调用setter完成下面的两步操作

// 等效的

[_room release];

_room = nil;

[super dealloc];

}