Effective Rust

Chapter 2. Traits

The second core pillar of Rust’s type system is the use of traits, which allow the encoding of behavior that is common across distinct types. A trait is roughly equivalent to an interface type in other languages, but they are also tied to Rust’s generics (Item 12), to allow interface reuse without runtime overhead.

The Items in this chapter describe the standard traits that the Rust compiler and the Rust toolchain make available, and provide advice on how to design and use trait-encoded behavior.

Item 10: Familiarize yourself with standard traits

Rust encodes key behavioral aspects of its type system in the type system itself, through a collection of fine-grained standard traits that describe those behaviors (see Item 2).

Many of these traits will seem familiar to programmers coming from C++, corresponding to concepts such as copy-constructors, destructors, equality and assignment operators, etc.

As in C++, it’s often a good idea to implement many of these traits for your own types; the Rust compiler will give you helpful error messages if some operation needs one of these traits for your type and it isn’t present.

Implementing such a large collection of traits may seem daunting, but most of the common ones can be automatically applied to user-defined types, using derive macros. These derive macros generate code with the “obvious” implementation of the trait for that type (e.g., field-by-field comparison for Eq on a struct); this normally requires that all constituent ...