Question

Can I use

self = nil 

in an instance method so that when the method execution ends, I can use an if statement in the main class:

if (myInstance) 

to check if something went wrong ?

thanks

Answer 1

You can do that, but it does not have the effect you want.

consider your objc method’s signature for -[NSArray count] to have the following C function signature:

NSUInteger NSArray_count(NSArray * self, SEL _cmd) {
   self = nil; // ok - this is a variable, local to the function (method).
               // now all messages to `self` will do nothing - in this method only.
   ...
}

since the pointer you assign to nil is a variable local to the method, it does not actually affect the instance externally. it changes the pointer variable in the method’s scope. that variable is the argument passed. in effect, it means that you have set the local argument to nil, but the rest of the world does not acknowledge this change.