E0474: Linear field dropped by destructure

Explanation

A field access on a struct declared linear consumes and destructures the smallest enclosing declared-linear place. Rue rejects that access when the residue contains another linear value, because destroying the residue would silently discard its must-consume obligation. A struct that is only linear by infection instead uses ordinary partial-move rules.

Likely cause

Code projects one field from a declared-linear struct while a sibling field, nested field, or residual array element also carries a linear value. Consume the whole declared-linear value, or restructure the operation so every linear component is explicitly consumed.

Examples

Destructure a declared-linear value with linear residue

linear struct Token { value: i32 }
linear struct Holder { token: Token, tag: i32 }
fn main() -> i32 {
    let holder = Holder { token: Token { value: 1 }, tag: 41 };
    holder.tag
}

Consume the declared-linear value explicitly

linear struct Token { value: i32 }
linear struct Holder { token: Token, tag: i32 }
fn main() -> i32 {
    let holder = Holder { token: Token { value: 1 }, tag: 41 };
    @drop(holder);
    0
}

References

• Declared-linear destructuring cannot drop linear residue