What does -> mean?

Question

I'm a relative newbie to Objective-C (only studied Arron Hillegras's book) and am confused by the following snippit of code I've found in one of Apple's code examples, in particular what does the -> mean?

-(id) initWithNumbers:(NSArray *)numbers
{
    self = [super init];
    if (self != nil)
    { 
       self->_numbers = [numbers copy];
    }
    return self;
}

In the header file _numbers is declared as

NSNumber * _number;

( the underscore has some significance from what I recall reading somewhere but that too eludes me at the moment.

Thanks Robin

Answer 1

-> is a normal C operator for accessing the members of a pointer to a struct; the . operator is for accessing members of a struct. Thus:

a->b

is translated to

(*a).b

Since Objective-C objects are pointers to structs underneath it all, this works for accessing instance variables.