Structs, enums, and traits definitions can also be provided with constant field members. They can be used in cases where you need to share a constant among them. Take, for example, a scenario where we have a Circle trait that's is meant to be implemented by different circular shape types. We can add a PI constant to the Circle trait, which can be shared by any type that has an area property and relies on value of PI for calculating the area:
// trait_constants.rs
trait Circular {
const PI: f64 = 3.14;
fn area(&self) -> f64;
}
struct Circle {
rad: f64
}
impl Circular for Circle {
fn area(&self) -> f64 {
Circle::PI * self.rad * self.rad
}
}
fn main() {
let c_one = Circle { rad: 4.2 };
let c_two = Circle { rad: 75.2 };
println!("Area of circle one: {}", c_one.area());
println!("Area of circle two: {}", c_two.area());
}We can also have consts in structs and enums:
// enum_struct_consts.rs enum...