Adapter Pattern in Rust: Overcoming the Orphan Rule with Newtype and Extension Traits

Rust's Orphan Rule prevents implementing external traits on external types, which creates friction when bridging unrelated crates. The adapter pattern — wrapping an external type in a newtype struct — solves this by giving you ownership of the type in the impl block. The post walks through the pattern step by step: starting with a basic owned adapter, then a reference-based adapter with lifetimes, and finally using extension traits to make the API ergonomic. A practical axum + eyre integration example shows how to map eyre::Report errors to HTTP responses (500, 404, 403) using multiple specialized adapters and ResultExt/ErrExt extension traits. The post also covers Deref/AsRef tradeoffs on adapter types, field visibility conventions, and when crate-specific alternatives like serde's remote syntax may be preferable.