At this point you know how to use functions to organize code and built-in types to organize data. The next step is to learn how to build your own types to organize both code and data. This is a big topic; it will take a few chapters to get there.
We have used many of Julia’s built-in types; now we are going to define a new type. As an example, we will create a type called
Point that represents a point in two-dimensional space.
In mathematical notation, points are often written in parentheses with a comma separating the coordinates. For example, represents the origin, and represents the point units to the right and units up from the origin.
There are several ways we might represent points in Julia:
We could store the coordinates separately in two variables,
We could store the coordinates as elements in an array or tuple.
We could create a new type to represent points as objects.
Creating a new type is more complicated than the other options, but it has advantages that will be apparent soon.
A programmer-defined composite type is also called a struct. The
struct definition for a point looks like this:
The header indicates that the new struct is called
Point. The body defines the attributes or fields of the struct. The
Point struct has two fields:
A struct is like a factory for creating objects. To create a point, you call
Point as if it were a function having ...