A union expression does not have exactly one field.
Erroneous code example:
union Bird {
pigeon: u8,
turtledove: u16,
}
let bird = Bird {}; // error
let bird = Bird { pigeon: 0, turtledove: 1 }; // error
RunThe key property of unions is that all fields of a union share common storage. As a result, writes to one field of a union can overwrite its other fields, and size of a union is determined by the size of its largest field.
You can find more information about the union types in the Rust reference.
Working example:
union Bird {
pigeon: u8,
turtledove: u16,
}
let bird = Bird { pigeon: 0 }; // OK
Run