Summary: Automatic Reference Counting (ARC) dramatically simplifies memory management in Objective-C. This session introduces what ARC is, how it is implemented and how to migrate to ARC. Apple asks every developer to move Objective-C code to ARC.
Problems of memory management:
Many (new) developers do not understand reference counting. They don’t know when to retain/release/autorelease. Memory leaks and the app crashes.
What is ARC?
ARC is automatic object memory management. The compiler adds retain/release calls. It still uses reference counting. ARC is not Garbage collection. ARC is compile-time memory management, not run-time memory management.
If we write a stack, our code without ARC will be:
@implementation Stack { NSMutableArray *_array; }
- (id) init {
if (self = [super init])
_array = [[NSMutableArray array] retain];
return self;
}
- (void) push: (id) x {
[_array addObject: x];
}
- (id) pop {
id x = [[_array lastObject] retain];
[_array removeLastObject];
return [x autorelease];
}
- (void) dealloc { [_array release]; [super dealloc]; }
@end
With ARC:
@implementation Stack { NSMutableArray *_array; }
- (id) init {
if (self = [super init])
_array = [NSMutableArray array];
return self;
}
- (void) push: (id) x {
[_array addObject: x];
}
- (id) pop {
id x = [_array lastObject];
[_array removeLastObject];
return x;
}
@end
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