Reference Count Style Memory Management

• A variable hold the objects generate by itself

1

id obj = [[NSObject alloc] init];

• A variable can hold the objects generate by other variables

1
2

id obj = [NSMutableArray array];
[obj retain];

• If the objects of a variable are no longer needed, the variable can release the objects held by itself

1
2
3
4
5
6
7
8

// Generate by itself and hold the objects by itself
id obj = [[NSObject alloc] init];
[obj release];

// Generate by others and hold the objects by itself
id obj = [NSMutableArray array];
[obj retain];
[obj release];

• A variable cannot release the objects held by others

1
2

id obj1 = [obj0 object];
[obj1 release];    // error

ARC Rules

• Can’t use retain / release / retainCount / autorelease

  • Memory management is the compiler’s job, so there is no need to use this methods
  • This methods is need to use when the ARC is invalid

• Can’t use NSAllocateObject / NSDeallocateObject

  • When ARC is available, the methods NSAllocateObject and NSDeallocateObject are both forbidden

• Don’t call dealloc explicitly

  • When the object is abandoned, dealloc is called automatically no matter ARC is available or not

• Using @autoreleasepool instead of using NSAutoreleasePool

• Object type variables can’t be a member of structure

  • Structure can’t manage the life circle of its member

Bonus: The Diffence Between Objective-C Objects and Core Foundation Objects

• Objective-C objects are generated by Foundation Framework
• Core foundation objects are generated by Core Foundation Framework