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Sep 25, 2018
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Grammar: Add enum expression. #428

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36 changes: 34 additions & 2 deletions src/expressions/enum-variant-expr.md
View file
Original file line number Diff line number Diff line change
@@ -1,7 +1,30 @@
# Enumeration Variant expressions

Enumeration variants can be constructed similarly to structs, using a path to
an enum variant instead of to a struct:
> **<sup>Syntax</sup>**\
> _EnumerationVariantExpression_ :\
> &nbsp;&nbsp; &nbsp;&nbsp; _EnumExprStruct_\
> &nbsp;&nbsp; | _EnumExprTuple_\
> &nbsp;&nbsp; | _EnumExprFieldless_
>
> _EnumExprStruct_ :\
> &nbsp;&nbsp; [_PathInExpression_] `{` _EnumExprFields_<sup>?</sup> `}`
>
> _EnumExprFields_ :\
> &nbsp;&nbsp; &nbsp;&nbsp; _EnumExprField_ (`,` _EnumExprField_)<sup>\*</sup> `,`<sup>?</sup>
>
> _EnumExprField_ :\
> &nbsp;&nbsp; &nbsp;&nbsp; [IDENTIFIER]\
> &nbsp;&nbsp; | ([IDENTIFIER] | [TUPLE_INDEX]) `:` [_Expression_]
>
> _EnumExprTuple_ :\
> &nbsp;&nbsp; [_PathInExpression_] `(`\
> &nbsp;&nbsp; &nbsp;&nbsp; ( [_Expression_] (`,` [_Expression_])<sup>\*</sup> `,`<sup>?</sup> )<sup>?</sup>\
> &nbsp;&nbsp; `)`
>
> _EnumExprFieldless_ : [_PathInExpression_]

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

```rust
# enum Message {
@@ -13,3 +36,12 @@ 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][structs], except they do not support base update with the `..` syntax.

[IDENTIFIER]: identifiers.html
[TUPLE_INDEX]: tokens.html#integer-literals
[_Expression_]: expressions.html
[_PathInExpression_]: paths.html#paths-in-expressions
[structs]: expressions/struct-expr.html