It seems Rust is built for Parse, don't validate. The invariants are encoded in the type system.

• https://docs.rs/nonempty/latest/nonempty/ crates ensure .first() always return
• AbsPathBug is useful because Subsequent code doesn't have to validate the the path is absolute. The type enforces it.
• NonZero ensure the 0 value doesn't exist on the number type. Rust cam also optimize the memory used for Option<NonZero> by using the zero value as None.