# Traits

Traits are probably Rust's most complex feature, supporting a wide range of use cases and design tradeoffs. Patterns of trait usage are still emerging.

### Know whether a trait will be used as an object. [FIXME: needs RFC]

Trait objects have some significant limitations: methods invoked through a trait object cannot use generics, and cannot use `Self` except in receiver position.

When designing a trait, decide early on whether the trait will be used as an object or as a bound on generics; the tradeoffs are discussed in each of the linked sections.

If a trait is meant to be used as an object, its methods should take and return trait objects rather than use generics.

### Default methods [FIXME]

> [FIXME] Guidelines for default methods.