Missing field in struct literal

struct User { id: u64, name: String, email: String }
let u = User { id: 1, name: "ada".into() };
// E0063: missing field `email`

Every field must be set somewhere — Rust does not invent defaults silently. The compiler refuses partial construction.

- Provide the missing fields. - Use ..Default::default() if the struct implements Default: User { id: 1, name: "ada".into(), ..Default::default() }. - Wrap optional fields in Option<T> so callers can skip them while still satisfying the type. - For evolving structs, #[non_exhaustive] plus a builder forces controlled construction.