Trait Ord

pub trait Ord: Eq + PartialOrd {
    // Required method
    fn cmp(&self, other: &Self) -> Ordering;

    // Provided methods
    fn max(self, other: Self) -> Self
       where Self: Sized { ... }
    fn min(self, other: Self) -> Self
       where Self: Sized { ... }
    fn clamp(self, min: Self, max: Self) -> Self
       where Self: Sized { ... }
}

Trait for types that form a total order.

Implementations must be consistent with the PartialOrd implementation, and ensure max, min, and clamp are consistent with cmp:

• partial_cmp(a, b) == Some(cmp(a, b)).
• max(a, b) == max_by(a, b, cmp) (ensured by the default implementation).
• min(a, b) == min_by(a, b, cmp) (ensured by the default implementation).
• For a.clamp(min, max), see the method docs (ensured by the default implementation).

Violating these requirements is a logic error. The behavior resulting from a logic error is not specified, but users of the trait must ensure that such logic errors do not result in undefined behavior. This means that unsafe code must not rely on the correctness of these methods.

Corollaries

From the above and the requirements of PartialOrd, it follows that for all a, b and c:

• exactly one of a < b, a == b or a > b is true; and
• < is transitive: a < b and b < c implies a < c. The same must hold for both == and >.

Mathematically speaking, the < operator defines a strict weak order. In cases where == conforms to mathematical equality, it also defines a strict total order.

Derivable

This trait can be used with #[derive].

When derived on structs, it will produce a lexicographic ordering based on the top-to-bottom declaration order of the struct’s members.

When derived on enums, variants are ordered primarily by their discriminants. Secondarily, they are ordered by their fields. By default, the discriminant is smallest for variants at the top, and largest for variants at the bottom. Here’s an example: