Creating a data structure is one of the ways to add a new data type to Rust. A data structure is a group of variables that have been attached to each other, resulting in a single new data type that means all of these, together.

A new structure is defined using the struct keyword:

pub struct Constrained {
    pub min: i32,
    pub max: i32,
    current: i32,
}

Here, we've defined a structure called Constrained, which is made up of three different 32-bit unsigned integer variables. The structure itself is public, meaning that it can be used outside of the module where it's defined.

The min and max contained variables are also public, but that means something slightly different. It means that anywhere we have a Constrained value, we can access the min and max contained values directly. The current value, on the other hand, is private, which means that it can be directly accessed only within the module where the structure is defined. We can define functions in that module with the express purpose of accessing the data contained in private structure members, but the members themselves are not part of the structure's public interface, even if the structure itself is public.

To access min and max, we can use the same . symbol that we've seen previously in a few places. So, if cons is a mutable Constrained value, then we can do things like this:

cons.min = 5;