enum

Declares a sum type: a value is exactly one of its variants.

Variants can carry no data, a tuple payload or named fields. Build them with Enum::Variant and take them apart with match. With #[repr(int)] (or string, float, bool), each variant is backed by a literal (Ok = 200). An enum may be generic.

enum Shape {
    Circle(float),
    Rect { w: float, h: float },
    Empty,
}

fn area(Shape s) -> float {
    return match s {
        Shape::Circle(r) => 3.14 * r * r,
        Shape::Rect { w, h } => w * h,
        Shape::Empty => 0.0,
    };
}

See also#

• string
• float
• bool
• fn: Declares a function, a method, or (written in an expression) an anonymous function.
• let: Declares a mutable local variable.
• const: Declares a binding that cannot be reassigned: a local, a module constant, or a class field that is set only by new.
• static: Declares a module-level or class-level slot shared by the whole program, or a method without self.
• readonly: A read-only view of a value: nothing reachable through it can be changed.