Deref

The Deref derive macro implements std::ops::Deref, forwarding to an inner field. This is useful for the newtype pattern — wrapping a type while exposing its methods directly.

Single-Field Structs

For structs with one field, Deref automatically targets that field. No attribute needed.

Tuple Struct

use moxy::Deref;

#[derive(Deref)]
struct Email(String);

let email = Email("john@example.com".into());
assert_eq!(email.len(), 16); // delegates to String::len

Named Struct

use moxy::Deref;

#[derive(Deref)]
struct Email {
    raw: String,
}

let email = Email { raw: "john@example.com".into() };
assert_eq!(email.len(), 16);

Multi-Field Structs

When a struct has multiple fields, mark the deref target with #[moxy(deref)]:

use moxy::Deref;

#[derive(Deref)]
struct User {
    name: String,
    #[moxy(deref)]
    email: String,
    phone: String,
}

let user = User {
    name: "John".into(),
    email: "john@example.com".into(),
    phone: "".into(),
};

assert_eq!(user.len(), 16); // delegates to email.len()

Warning

Omitting #[moxy(deref)] on a multi-field struct is a compile error — the macro cannot infer which field to delegate to.

Without #[moxy(deref)] on a multi-field struct, the macro will produce a compile error asking you to specify which field to target.

Use Cases

Note

Deref is intended for the newtype pattern. Delegating to an unrelated field in a multi-field struct can cause surprising behavior for callers who use * or method resolution.

The Deref derive is ideal for the newtype pattern:

use moxy::Deref;

#[derive(Deref)]
struct Username(String);

#[derive(Deref)]
struct Port(u16);

let name = Username("alice".into());
let port = Port(8080);

// Access all String methods on Username
assert!(name.starts_with("ali"));
assert_eq!(name.to_uppercase(), "ALICE");

// Access all u16 methods on Port
assert_eq!(port.leading_zeros(), 3);