Why sometimes 'self' isn't available while debugging with lldb?

Question

A lot of time (when it\'s not every time) I got the following error when I try to print objects on lldb. Is there some build/debug configuration to change or is this an erro

Answer 1

Because it's optimized away. Let's use an example:

void f(int self) {
  // Here, "self" is live:Its value is used in the call to NSLog()
  NSLog(@"I am %d",self);
  // Here, "self" is dead: Its value is never used.
  // I could do self=0 or self=self*self and nobody would know.
  // An optimizing compiler will typically optimize it away.
  // It might still be on the stack (in the parameters passed to NSLog())
  // but the compiler shouldn't assume this.
  NSLog(@"Another function call: %d", 1);
  // If "self" was on the stack, it will probably now have been overwritten.
}

Compilers do a lot of things to make your code faster/smaller; forgetting about variables which are no longer needed is a very common optimization.