Missing field in struct construction

Why this fires¶

A struct literal (Struct { ... }) omits a field that has no default value and no zero-value fallback. Every non-defaultable field must be provided explicitly at construction time.

struct User {
    name: str,
    age: int,
}

let u = User { name: "Ana" }
//      ^^^^^^^^^^^^^^^^^^^^ error[TE107]: missing field 'age' in construction of 'User'

Fix it¶

1. Provide the missing field¶

let u = User { name: "Ana", age: 30 }   // ok

2. Give the field a default¶

If the field usually has the same value, declare a default so callers can omit it:

struct User {
    name: str,
    age: int = 0,
}

let u = User { name: "Ana" }            // ok — age defaults to 0

3. Spread from an existing value¶

A trailing ..expr spread contributes its fields to construction coverage, so omitted fields are filled from expr instead of erroring:

struct User { name: str, age: int }

fn rename(u: User, new_name: str) -> User {
    return User { name: new_name, ..u }  // ok — `age` comes from `u`
}

See also¶

• TE108 — a field can't get a @derive(Default) default because its own type has no Default.
• TE109 — a field's type can't be inferred from its default value.
• TE128 — spread source (..expr) must be a struct or record.
• /docs/data-structures#structs — struct construction and field defaults.