Pointer and reference

Middle PRO

Essence

In Objective-C (as in C) there are no references as a language construct — only values and pointers. A "reference to an object" in casual speech means a pointer NSString *s: the variable holds the address of a heap object, not the object itself. Assigning a pointer copies the address, so both variables point to the same object; under ARC the assignment also does a retain.

• Scalars and structs (NSInteger, CGRect) are passed to methods by value — a copy; changes inside are invisible outside.
• Objects are passed as pointers: a method can mutate the object ([array addObject:]) but cannot reassign the caller's variable — it received a copy of the address.