Explain class loading lifecycle in Objective-C runtime

Objective-C classes go through allocation, initialization, and +load execution before main() starts.

When an app starts, the Mach-O loader loads binaries into memory. The Objective-C runtime then registers classes, categories, and protocols. +load methods are executed before main(), followed by +initialize when the class is first used. This lifecycle is critical for swizzling, dependency setup, and static configuration.