[rustc.git] / compiler / rustc_error_codes / src / error_codes / E0784.md

A union expression does not have exactly one field.

Erroneous code example:

```compile_fail,E0784
union Bird {
    pigeon: u8,
    turtledove: u16,
}

let bird = Bird {}; // error
let bird = Bird { pigeon: 0, turtledove: 1 }; // error
```

The 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
```

[Rust reference]: https://doc.rust-lang.org/reference/items/unions.html
Commit	Line	Data
94222f64 XL	1	A union expression does not have exactly one field.
	2
	3	Erroneous code example:
	4
	5	```compile_fail,E0784
	6	union Bird {
	7	pigeon: u8,
	8	turtledove: u16,
	9	}
	10
	11	let bird = Bird {}; // error
	12	let bird = Bird { pigeon: 0, turtledove: 1 }; // error
	13	```
	14
	15	The key property of unions is that all fields of a union share common storage.
	16	As a result, writes to one field of a union can overwrite its other fields, and
	17	size of a union is determined by the size of its largest field.
	18
	19	You can find more information about the union types in the [Rust reference].
	20
	21	Working example:
	22
	23	```
	24	union Bird {
	25	pigeon: u8,
	26	turtledove: u16,
	27	}
	28
	29	let bird = Bird { pigeon: 0 }; // OK
	30	```
	31
	32	[Rust reference]: https://doc.rust-lang.org/reference/items/unions.html