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Add 2018 edition keywords. #442

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Oct 6, 2018
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Add 2018 edition keywords. #442

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22 changes: 19 additions & 3 deletions src/keywords.md
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Original file line number Diff line number Diff line change
Expand Up @@ -57,6 +57,11 @@ be used as the names of:
> KW_WHERE : `where`\
> KW_WHILE : `while`

The following keywords were added beginning in the 2018 edition.

> **<sup>Lexer 2018+</sup>**\
> KW_DYN : `dyn`

## Reserved keywords

These keywords aren't used yet, but they are reserved for future use. They have
Expand All @@ -78,6 +83,13 @@ them to use these keywords.
> KW_VIRTUAL : `virtual`\
> KW_YIELD : `yield`

The following keywords are reserved beginning in the 2018 edition.

> **<sup>Lexer 2018+</sup>**\
> KW_ASYNC : `async`\
> KW_AWAIT : `await`\
> KW_TRY : `try`

## Weak keywords

These keywords have special meaning only in certain contexts. For example, it
Expand All @@ -92,12 +104,16 @@ is possible to declare a variable or method with the name `union`.
// error[E0262]: invalid lifetime parameter name: `'static`
fn invalid_lifetime_parameter<'static>(s: &'static str) -> &'static str { s }
```
* `dyn` denotes a [trait object] and is a keyword when used in a type position
* In the 2015 edition, [`dyn`] is a keyword when used in a type position
followed by a path that does not start with `::`.

Beginning in the 2018 edition, `dyn` has been promoted to a strict keyword.

> **<sup>Lexer</sup>**\
> KW_UNION : `union`\
> KW_STATICLIFETIME : `'static`\
> KW_STATICLIFETIME : `'static`
>
> **<sup>Lexer 2015</sup>**\
> KW_DYN : `dyn`

[items]: items.html
Expand All @@ -110,4 +126,4 @@ is possible to declare a variable or method with the name `union`.
[Crates]: crates-and-source-files.html
[union]: items/unions.html
[variants]: items/enumerations.html
[trait object]: types.html#trait-objects
[`dyn`]: types.html#trait-objects
13 changes: 8 additions & 5 deletions src/types.md
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Expand Up @@ -676,11 +676,14 @@ For example, given a trait `Trait`, the following are all trait objects:
* `dyn 'static + Trait`.
* `dyn (Trait)`

If the first bound of the trait object is a path that starts with `::`, then the
`dyn` will be treated as a part of the path. The first path can be put in
parenthesis to get around this. As such, if you want a trait object with the
trait `::your_module::Trait`, you should write it as
`dyn (::your_module::Trait)`.
> **Edition Differences**: In the 2015 edition, if the first bound of the
> trait object is a path that starts with `::`, then the `dyn` will be treated
> as a part of the path. The first path can be put in parenthesis to get
> around this. As such, if you want a trait object with the trait
> `::your_module::Trait`, you should write it as `dyn (::your_module::Trait)`.
>
> Beginning in the 2018 edition, `dyn` is a true keyword and is not allowed in
> paths, so the parentheses are not necessary.

> Note: For clarity, it is recommended to always use the `dyn` keyword on your
> trait objects unless your codebase supports compiling with Rust 1.26 or lower.
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