NSObject

NSObject is the root class of most Objective-C class hierarchies in Apple’s Cocoa and Cocoa Touch frameworks. Defined by the Foundation framework, it provides the basic object behavior and runtime features shared by objects in an application, and it serves as a convenient base class for bridging to Swift.

Core responsibilities include object initialization, memory management hooks, and basic introspection. The standard initialization path begins with -init, while -dealloc serves as a hook for cleanup in non-ARC environments; in Automatic Reference Counting (ARC) contexts, deallocation is still used to free non-ARC resources, whereas explicit retain, release, and autorelease calls are typically avoided. The root class also offers basic identity and comparison primitives: -isEqual: and -hash implement object equality semantics, with default behavior based on object identity unless overridden by subclasses.

NSObject provides several facilities for runtime reflection and messaging. Methods such as -class, -superclass, -respondsToSelector:, -isKindOfClass:, -isMemberOfClass:, and -conformsToProtocol: enable introspection and dynamic behavior. It offers a string representation via -description, and related methods for debugging and logging. The class also supports the Objective-C message-sending and forwarding mechanisms through methods like -methodSignatureForSelector: and -forwardInvocation:, enabling dynamic method resolution or forwarding to other objects when a selector is unrecognized.

Other common capabilities include the performSelector: family of methods for delayed or thread-specific message delivery, and basic integration with Foundation features such as Key-Value Coding (KVC) and Key-Value Observing (KVO). In modern development, ARC reduces the emphasis on manual memory management, but the relevant methods remain available for compatibility with older code and certain manual-resource-cleanup scenarios.