Fundamentals

Before Swift closures, Objective-C had blocks. The syntax is different, but the power is the same—here's how to use them effectively.

Every Objective-C class inherits from NSObject (usually). Here's what NSObject provides and why it matters for every object you create.

Both let you add methods to classes, but categories and class extensions serve different purposes. Here's when to use each.

Unlike C++ virtual methods, Objective-C uses dynamic message passing. Understanding this mechanism unlocks the language's full power.