nutype

nutype is a Rust proc macro crate (2.7M+ downloads) that generates validated newtypes with sanitization rules automatically. It eliminates the boilerplate of the newtype-pattern — private constructors, validation logic, trait impls — by declaring constraints declaratively.

This is parse-dont-validate made ergonomic: define a newtype with its validation rules, and nutype generates a type where invalid instances cannot exist. For manual newtype creation, derive-more handles the trait derivation boilerplate. See type-driven-development for the full methodology.