rust/src/doc/trpl/tuple-structs.md

% Tuple Structs

Rust has another data type that's like a hybrid between a tuple and a struct, called a tuple struct. Tuple structs do have a name, but their fields don't:

struct Color(i32, i32, i32);
struct Point(i32, i32, i32);

These two will not be equal, even if they have the same values:

# struct Color(i32, i32, i32);
# struct Point(i32, i32, i32);
let black = Color(0, 0, 0);
let origin = Point(0, 0, 0);

It is almost always better to use a struct than a tuple struct. We would write Color and Point like this instead:

struct Color {
    red: i32,
    blue: i32,
    green: i32,
}

struct Point {
    x: i32,
    y: i32,
    z: i32,
}

Now, we have actual names, rather than positions. Good names are important, and with a struct, we have actual names.

There is one case when a tuple struct is very useful, though, and that's a tuple struct with only one element. We call this the newtype pattern, because it allows you to create a new type, distinct from that of its contained value and expressing its own semantic meaning:

struct Inches(i32);

let length = Inches(10);

let Inches(integer_length) = length;
println!("length is {} inches", integer_length);

As you can see here, you can extract the inner integer type through a destructuring let, as we discussed previously in 'tuples.' In this case, the let Inches(integer_length) assigns 10 to integer_length.