自学方法

Question

I am reading some Objective-C code in a well-maintained GitHub repo. https://github.com/soffes/sskeychain/blob/master/SSKeychain.m

I came across some weird lines (at least weird to my eyes).

+ (NSArray *)allAccounts {
    return [self accountsForService:nil error:nil];
}

I was taught that self refers to the instance itself in an instance method. So what does self mean here, in a class method?

Answer 1

Inside class methods, self refers to the object representing the corresponding Class :

+ (NSArray *)allAccounts {
    NSLog("%@", [self description]); // Will print the name of the class
    return [self accountsForService:nil error:nil];
}

This is the same object that you get in an instance method when you call [self class] .

It is useful if you would like to call methods on the class polymorphically. For example, you can call [[self alloc] init] to create a new instance of the class on which the call is performed.