History of Obj-C Memory Management

Notes: https://en.wikipedia.org/wiki/Objective-C

1980s origins and early model

Objective-C was created in the early 1980s (by Brad Cox and Tom Love) as an object-oriented layer on C, adopting Smalltalk-style messaging.

Early Objective-C used manual reference counting; developers called retain (to take ownership) and release (to relinquish ownership) on objects. This Manual Retain-Release (MRR) model was the norm through the 1990s and 2000s. It provided deterministic memory management but relied on programmer discipline; forgetting a release caused leaks, while an extra release caused crashes.

2006 Obj-C 2.0 and garbage collection

In 2006, Apple announced Objective-C 2.0, introducing modern features and an optional garbage collector on Mac OS X (desktop). Under GC, retain/release calls became no-ops and a background thread automatically reclaimed objects (using a conservative generational collector). A zero-ing weak reference system was added (so __weak pointers would nil out on object deallocation). Notably, this GC was never available on iOS; iOS always stuck to explicit reference counting. Garbage collection on macOS proved to have performance and complexity trade-offs, and Apple deprecated GC in OS X 10.8 (2012) in favor of a new compile-time approach called ARC.

2011 Introduction of ARC

Automatic Reference Counting (ARC) was introduced in 2011 (LLVM 3.0, Xcode 4.2) and fundamentally changed how memory is managed in Objective-C. ARC is not a runtime garbage collector, but a compiler feature.

The compiler statically inserts retain, release, and autorelease calls during build, based on code analysis, so that developers no longer write them by hand. This significantly reduced memory management bugs while incurring no separate GC pause at runtime (ARC operations occur inline where needed).

With ARC’s arrival, Apple also added zeroing weak references and other qualifiers to the language (e.g. __weak, __strong, __autoreleasing, etc.) to safely handle common patterns (previously, Objective-C object pointers could only be strong or unsafe). ARC was a major evolution that preserved deterministic deallocation (object life cycle is tied to last reference release) without the developer burden of manual calls.

2012 and later

Since ARC, Objective-C’s memory model has remained primarily ARC-based reference counting. Notable changes after ARC’s introduction have been more incremental. For example, Apple removed support for NSZone custom allocators; memory zones were a legacy concept and “are no longer used by the modern Objective-C runtime”. Other improvements included literals and compiler optimizations, but the fundamental memory management approach (ARC on top of retain/release semantics) has been stable since 2011.

AFAIK, virtually all Objective-C code is compiled with ARC, though the runtime still supports MRR for backward compatibility or special cases. iOS and macOS frameworks have been ARC-compatible for years, and Apple’s templates default to ARC. The old GC is long gone (it’s not present in 64-bit runtime and was fully removed from macOS years ago), solidifying ARC as the core memory management scheme for Objective-C.