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Document current limitation of type aliases on enums #984

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Document current limitation of type aliases on enums
bstrie Mar 18, 2021
d068638
Add error code
bstrie Mar 18, 2021
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21 changes: 21 additions & 0 deletions src/items/type-aliases.md
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@@ -1,3 +1,4 @@

# Type aliases

> **<sup>Syntax</sup>**\
Expand DownExpand Up@@ -33,10 +34,30 @@ let _ = TypeAlias(5); // Doesn't work
A type alias without the [_Type_] specification may only appear as an
[associated type] in a [trait].

A type alias to an enum cannot refer to the enum's variants within a [use declaration]:

```rust,edition2018,compile_fail,E0432
mod my_mod {
pub enum MyEnum {
MyVariant
}

pub type TypeAlias = MyEnum;
}

use my_mod::MyEnum; // OK
use my_mod::MyEnum::MyVariant; // OK
use my_mod::TypeAlias; // OK
use my_mod::TypeAlias::MyVariant; // Doesn't work

let _ = my_mod::TypeAlias::MyVariant; // OK
```

[IDENTIFIER]: ../identifiers.md
[_GenericParams_]: generics.md
[_WhereClause_]: generics.md#where-clauses
[_Type_]: ../types.md#type-expressions
[associated type]: associated-items.md#associated-types
[trait]: traits.md
[type]: ../types.md
[use declaration]: use-declarations.md