Question

I don’t understand why variables are declared as static in Objective-c class methods?

What is the scope of the static variables?

Answer 1

static variables don’t get destroyed when their stack frame is popped off the stack (normal variables do, otherwise you’d get epic memory leaks). See them as global variables you can only access locally. They’ll stay alive till the entire program terminates.

Example:

+ (id)sharedInstance {
  static singletonInstance = nil; // for example
  if (singletonInstance == nil) {
    singletonInstance = [[self alloc] init];
  }
  return singletonInstance;
}