ContextQMD
Back to Comprehensive Rust

Supertraits / Trait Dependencies

src/idiomatic/polymorphism/refresher/supertraits.md

latest1.2 KB
Original Source
<!-- Copyright 2025 Google LLC SPDX-License-Identifier: CC-BY-4.0 -->

Supertraits / Trait Dependencies

Traits can be extended by new traits.

rust,editable
# // Copyright 2025 Google LLC
# // SPDX-License-Identifier: Apache-2.0
#
pub trait Animal {
    /* methods common to all animals */
}

pub trait Mammal: Animal {
    /* methods only for mammals */
}

// From stdlib

pub trait Ord: Eq + PartialOrd {
    /* methods for Ord */
}
<details>

  • When authoring a trait, you can specify traits that a type must also. These are called supertraits.

    For the example above, any type that implements Mammal must also implement Animal.

  • These hierarchies of traits let us design systems around the behavior of complex real-world taxonomies (like fauna, machine hardware, operating system specifics, etc).

  • This is distinct from object inheritance! But it looks similar.

    • Object inheritance allows for overrides and brings in the behavior of the inherited types by default.

    • A trait having a supertrait doesn't mean that trait can override method implementations as default implementations.

ref:

</details>