autoreleased

Autoreleased is a term used in memory management for Objective-C and related Cocoa frameworks to describe objects that have been marked to be released automatically by an autorelease pool. An autoreleased object is not freed immediately after being autoreleased; instead, its retain count will be decremented when the autorelease pool is drained, which typically occurs at the end of the current run loop iteration or when a code block explicitly drains its pool.

Autorelease pool is a mechanism that collects objects that have received an autorelease message. The pool releases each object when it is drained. Pools can be nested; inner pools drain first and then propagate to outer pools. In older code you might see NSAutoreleasePool blocks, while modern code uses @autoreleasepool { ... } blocks to create and drain pools explicitly.

Objects are often autoreleased as part of factory methods or convenience constructors. This pattern allows methods to return objects without transferring ownership to the caller, reducing the need for immediate release calls.

Examples include methods like [NSDate date] or [NSString stringWithFormat:...] which return autoreleased objects. The autorelease mechanism helps manage temporary objects without requiring the caller to manage their lifetimes directly.

Impact and evolution: Autorelease pools were essential in pre-ARC memory management, providing a balance between object lifetimes and performance. With Automatic Reference Counting (ARC), most retain/release/autorelease calls are inserted automatically by the compiler, and developers use @autoreleasepool blocks primarily to limit the lifetime of temporary objects in long-running threads or non-ARC code. Legacy NSAutoreleasePool remains for compatibility, and autorelease semantics may still be encountered in bridging scenarios between Objective-C and other languages.