mirror of https://github.com/rust-lang/reference
Merge pull request #1022 from ehuss/ident-unicode
Expand on Unicode identifiers.
This commit is contained in:
commit
0fe357f176
|
@ -2,8 +2,8 @@
|
|||
|
||||
> **<sup>Lexer:<sup>**\
|
||||
> IDENTIFIER_OR_KEYWORD :\
|
||||
> XID_start XID_continue<sup>\*</sup>\
|
||||
> | `_` XID_continue<sup>+</sup>
|
||||
> XID_Start XID_Continue<sup>\*</sup>\
|
||||
> | `_` XID_Continue<sup>+</sup>
|
||||
>
|
||||
> RAW_IDENTIFIER : `r#` IDENTIFIER_OR_KEYWORD <sub>*Except `crate`, `self`, `super`, `Self`*</sub>
|
||||
>
|
||||
|
@ -12,29 +12,59 @@
|
|||
> IDENTIFIER :\
|
||||
> NON_KEYWORD_IDENTIFIER | RAW_IDENTIFIER
|
||||
|
||||
An identifier is any nonempty Unicode string of the following form:
|
||||
<!-- When updating the version, update the UAX links, too. -->
|
||||
Identifiers follow the specification in [Unicode Standard Annex #31][UAX31] for Unicode version 13.0, with the additions described below. Some examples of identifiers:
|
||||
|
||||
Either
|
||||
* `foo`
|
||||
* `_identifier`
|
||||
* `r#true`
|
||||
* `Москва`
|
||||
* `東京`
|
||||
|
||||
* The first character has property [`XID_start`].
|
||||
* The remaining characters have property [`XID_continue`].
|
||||
The profile used from UAX #31 is:
|
||||
|
||||
Or
|
||||
* Start := [`XID_Start`], plus the underscore character (U+005F)
|
||||
* Continue := [`XID_Continue`]
|
||||
* Medial := empty
|
||||
|
||||
* The first character is `_`.
|
||||
* The identifier is more than one character. `_` alone is not an identifier.
|
||||
* The remaining characters have property [`XID_continue`].
|
||||
> **Note**: Identifiers starting with an underscore are typically used to indicate an identifier that is intentionally unused, and will silence the unused warning in `rustc`.
|
||||
|
||||
> **Note**: [`XID_start`] and [`XID_continue`] as character properties cover the
|
||||
> character ranges used to form the more familiar C and Java language-family
|
||||
> identifiers.
|
||||
Identifiers may not be a [strict] or [reserved] keyword without the `r#` prefix described below in [raw identifiers](#raw-identifiers).
|
||||
|
||||
Zero width non-joiner (ZWNJ U+200C) and zero width joiner (ZWJ U+200D) characters are not allowed in identifiers.
|
||||
|
||||
Identifiers are restricted to the ASCII subset of [`XID_Start`] and [`XID_Continue`] in the following situations:
|
||||
|
||||
* [`extern crate`] declarations
|
||||
* External crate names referenced in a [path]
|
||||
* [Module] names loaded from the filesystem without a [`path` attribute]
|
||||
* [`no_mangle`] attributed items
|
||||
* Item names in [external blocks]
|
||||
|
||||
## Normalization
|
||||
|
||||
Identifiers are normalized using Normalization Form C (NFC) as defined in [Unicode Standard Annex #15][UAX15]. Two identifiers are equal if their NFC forms are equal.
|
||||
|
||||
[Procedural][proc-macro] and [declarative][mbe] macros receive normalized identifiers in their input.
|
||||
|
||||
## Raw identifiers
|
||||
|
||||
A raw identifier is like a normal identifier, but prefixed by `r#`. (Note that
|
||||
the `r#` prefix is not included as part of the actual identifier.)
|
||||
Unlike a normal identifier, a raw identifier may be any strict or reserved
|
||||
keyword except the ones listed above for `RAW_IDENTIFIER`.
|
||||
|
||||
[strict]: keywords.md#strict-keywords
|
||||
[`extern crate`]: items/extern-crates.md
|
||||
[`no_mangle`]: abi.md#the-no_mangle-attribute
|
||||
[`path` attribute]: items/modules.md#the-path-attribute
|
||||
[`XID_Continue`]: http://unicode.org/cldr/utility/list-unicodeset.jsp?a=%5B%3AXID_Continue%3A%5D&abb=on&g=&i=
|
||||
[`XID_Start`]: http://unicode.org/cldr/utility/list-unicodeset.jsp?a=%5B%3AXID_Start%3A%5D&abb=on&g=&i=
|
||||
[external blocks]: items/external-blocks.md
|
||||
[mbe]: macros-by-example.md
|
||||
[module]: items/modules.md
|
||||
[path]: paths.md
|
||||
[proc-macro]: procedural-macros.md
|
||||
[reserved]: keywords.md#reserved-keywords
|
||||
[`XID_start`]: http://unicode.org/cldr/utility/list-unicodeset.jsp?a=%5B%3AXID_Start%3A%5D&abb=on&g=&i=
|
||||
[`XID_continue`]: http://unicode.org/cldr/utility/list-unicodeset.jsp?a=%5B%3AXID_Continue%3A%5D&abb=on&g=&i=
|
||||
[strict]: keywords.md#strict-keywords
|
||||
[UAX15]: https://www.unicode.org/reports/tr15/tr15-50.html
|
||||
[UAX31]: https://www.unicode.org/reports/tr31/tr31-33.html
|
||||
|
|
Loading…
Reference in New Issue