Enums

Contents

Enums#

Discriminated unions; each variant can carry data.

enum Shape {
    Circle(f64),
    Rect { w: f64, h: f64 },
    Empty,
}

Construct a variant.

let s = Shape::Circle(2.0);

Match exhaustively; the compiler refuses to compile a non-total match.

match s {
    Shape::Circle(r)     => println!("area {}", 3.14 * r * r),
    Shape::Rect { w, h } => println!("area {}", w * h),
    Shape::Empty         => println!("nothing"),
}

Two enums in the stdlib do most of the heavy lifting.

enum Option<T> { Some(T), None }
enum Result<T, E> { Ok(T), Err(E) }

Option replaces null; Result replaces exceptions. See Option and Result.

References#

Contents