Constants

Constants are similar to immutable let variables; however, there are a few differences:

• Constants are always evaluated at compile-time.
• Constants can be declared both inside of a function and at global/impl scope.
• The mut keyword cannot be used with constants.

Declaration

To define a constant the const keyword is used followed by a name and an assignment of a value.

    const FOO = 5;

The example above hardcodes the value of 5 however function calls may also be used alongside built-in types.

impl self Constants

Constants can also be declared inside impl blocks. In this case, the constant is referred to as an associated constant.

struct Point {
    x: u64,
    y: u64,
}

impl Point {
    const ZERO: Point = Point { x: 0, y: 0 };
}

fn main() -> u64  {
    Point::ZERO.x
}