Programming in Objective-C, Sixth Edition

Fact 2: An Object Variable Is Really a Pointer

When you define an object variable such as a Fraction, as in

Fraction *myFract;

you’re really defining a pointer variable called myFract. This variable is defined to point to something of type Fraction, which is the name of your class. When you allocate a new instance of a Fraction, with

myFract = [Fraction alloc];

you’re allocating space to store a new Fraction object in memory (that is, space for a structure) and then storing the pointer to that structure that is returned inside the pointer variable myFract.

When you assign one object variable to another, as in

myFract2 = myFract1;

you’re simply copying pointers. Both variables end up pointing to the same structure stored somewhere in memory. Making ...