"Inheritance" in Rust: Supertraits

# // Copyright 2025 Google LLC
# // SPDX-License-Identifier: Apache-2.0
#
pub trait SuperTrait {}

pub trait Trait: SuperTrait {}

• In Rust, traits can depend on other traits. We're already familiar with Traits being able to have Supertraits.

• This looks superficially similar to inheritance.

• This is a mechanism like inheritance, but separates the data from the behavior.

• Keeps behavior in a state where it's easy to reason about.

• Makes what we aim to achieve with "multiple inheritance" easier too:

  We only care about what behavior a type is capable of at the point where we clarify we want that behavior (when bounding a generic by traits).

  By specifying multiple traits on a generic, we know that the type has the methods of all those traits.

• Does not involve inheritance of fields. A trait doesn't expose fields, only methods and associated types / constants.