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# Structures
There are three types of structures ("structs") that can be created using the
`struct` keyword:
* Tuple structs, which are, basically, named tuples.
* The classic [C structs][c_struct]
* Unit structs, which are field-less, are useful for generics.
```rust,editable
// An attribute to hide warnings for unused code.
#![allow(dead_code)]
#[derive(Debug)]
struct Person {
name: String,
age: u8,
}
// A unit struct
struct Unit;
// A tuple struct
struct Pair(i32, f32);
// A struct with two fields
struct Point {
x: f32,
y: f32,
}
// Structs can be reused as fields of another struct
struct Rectangle {
// A rectangle can be specified by where the top left and bottom right
// corners are in space.
top_left: Point,
bottom_right: Point,
}
fn main() {
// Create struct with field init shorthand
let name = String::from("Peter");
let age = 27;
let peter = Person { name, age };
// Print debug struct
println!("{:?}", peter);
// Instantiate a `Point`
let point: Point = Point { x: 5.2, y: 0.4 };
let another_point: Point = Point { x: 10.3, y: 0.2 };
// Access the fields of the point
println!("point coordinates: ({}, {})", point.x, point.y);
// Make a new point by using struct update syntax to use the fields of our
// other one
let bottom_right = Point { x: 10.3, ..another_point };
// `bottom_right.y` will be the same as `another_point.y` because we used that field
// from `another_point`
println!("second point: ({}, {})", bottom_right.x, bottom_right.y);
// Destructure the point using a `let` binding
let Point { x: left_edge, y: top_edge } = point;
let _rectangle = Rectangle {
// struct instantiation is an expression too
top_left: Point { x: left_edge, y: top_edge },
bottom_right: bottom_right,
};
// Instantiate a unit struct
let _unit = Unit;
// Instantiate a tuple struct
let pair = Pair(1, 0.1);
// Access the fields of a tuple struct
println!("pair contains {:?} and {:?}", pair.0, pair.1);
// Destructure a tuple struct
let Pair(integer, decimal) = pair;
println!("pair contains {:?} and {:?}", integer, decimal);
}
```
### Activity
1. Add a function `rect_area` which calculates the area of a `Rectangle` (try
using nested destructuring).
2. Add a function `square` which takes a `Point` and a `f32` as arguments, and
returns a `Rectangle` with its top left corner on the point, and a width and
height corresponding to the `f32`.
### See also
[`attributes`][attributes], [raw identifiers][raw_identifiers] and [destructuring][destructuring]
[attributes]: ../attribute.md
[c_struct]: https://en.wikipedia.org/wiki/Struct_(C_programming_language)
[destructuring]: ../flow_control/match/destructuring.md
[raw_identifiers]: ../compatibility/raw_identifiers.md