Automatic reference counting

Automatic reference counting (ARC) is an automatic memory management strategy. Typically, the compiler will insert reference tracking code into the program to check every time an object in memory receives or loses a pointer.

Every time a new pointer is created, the reference count is incremented (+1). Every time a pointer moves, the reference count is decremented (-1). When there are no more references (0), the object is immediately destroyed and its memory is deallocated.

Because ARC is reliant on reference counts reaching 0, circular references can cause retain cycles leading to silent memory leaks. To mitigate this, languages often require the program to explicity declare one side of the relationship as a “weak” reference.