Enum variant expressions - The Rust Reference

# Enumeration Variant expressions

> Syntax
> EnumerationVariantExpression :
> EnumExprStruct
> | EnumExprTuple
> | EnumExprFieldless

> EnumExprStruct :
> PathInExpression `{` EnumExprFields? `}`

> EnumExprFields :
> EnumExprField (`,` EnumExprField)* `,`?

> EnumExprField :
> IDENTIFIER
> | (IDENTIFIER | TUPLE_INDEX) `:` Expression

> EnumExprTuple :
> PathInExpression `(`
> ( Expression (`,` Expression)* `,`? )?
> `)`

> EnumExprFieldless : PathInExpression

Enumeration variants can be constructed similarly to structs, using a path to an enum variant instead of to a struct:

    #![allow(unused_variables)]
    fn main() {
    enum Message {
        Quit,
        WriteString(String),
        Move { x: i32, y: i32 },
    }
    let q = Message::Quit;
    let w = Message::WriteString("Some string".to_string());
    let m = Message::Move { x: 50, y: 200 };
    }

Enum variant expressions have the same syntax, behavior, and restrictions as struct expressions, except they do not support base update with the `..` syntax.