How is self used?

self represents an instance of the class calling the method in instance methods, and the class itself in class methods. Its kind of hard to understand, but when implementing a class such as a view controller, sometimes you want to call some instance methods or reference some instance variables inside the class itself. for example. if we had a class named cat

@implementation Cat

- (void)meow {

    NSLog(@"meow");

}

you can see that Cat has an instance method called meow. lets add another method called eat that calls that meow method inside it. But since meow is an instance method, which are called on instances or objects, how do we call that method when we dont have an instance to call it on since we are currently implementing the class itself? The solution is to use the keyword self which represents an instance of the current class.

- (void)eat {
    NSLog(@"eating");
    [self meow];
}

using [self meow] basically says call the meow instance method on the current instance of Cat. in other languages instead of the keyword being self the keyword is this, which is a bit easier to understand. in java if we wanted to call the meow method we would use this.meow() where this refers to "this instance of cat"

so if we created a cat object and called the eat method

Cat *someCat = [[Cat alloc] init];
[someCat eat]; 

the compiler would go to the eat method of the cat class and execute the code there

- (void)eat {
    NSLog(@"eating");
    [self meow]; //self here refers to the instance of cat that called the eat method, which is someCat
}

since someCat was the instance that called the method, self refers to the someCat object

when working inside class methods, using self just refers to the class itself. So you can use self to call class level methods etc. this way of using self is a lot easier to understand since its more simple. if you need to call a class method or refer to the class itself inside a class implementation, you can just use self ie [self someClassMethod] which is the same as [Classname someClassmethod]