Types

The type system in Objective-C is a little bit more disparate than Swift. This is because the structures and enumerations in Objective-C come from C. Only classes and categories come from the Objective-C extension.

Structures

In Swift, structures are very similar to classes, but in Objective-C, they are much more different. Structures in Objective-C are essentially just a way of giving a name to a collection of individual types. They cannot contain methods. Even more restrictive than that, structures can't contain Objective-C types. That leaves us with only the basic possibilities:

struct Cylinder {
    var radius: Int
    var height: Int
}
var c = Cylinder(radius: 10, height: 10)

typedef struct {
    int radius;
    int height;
} Cylinder;
Cylinder c;
c.radius = 10;
c.height = 5;

Structs in Objective-C start with the typedef keyword, which is the short form of the phrase type definition. That is then followed by the struct keyword and the different components of the structure contained...