Using a Rust macro for concise newtypes

- A **newtype** in Rust is a wrapper around an existing type (e.g., `struct Email(String)`) that lets you treat it as a distinct type — adding type safety and custom methods without runtime overhead. - Writing newtypes manually in Rust requires repetitive boilerplate trait implementations (e.g., `Deref`, `From`, `Display`). The article's macro automates this, letting developers define newtypes concisely with one line of code. - Macros in Rust are code that writes other code at compile time, reducing repetitive patterns. They are widely used in Rust for boilerplate reduction, but must be understood to avoid confusing syntax. - This matters because newtypes are a common Rust idiom for enforcing invariants (e.g., ensuring a string is a valid email) and making APIs more expressive. Automating them improves developer productivity and reduces errors.