mirror of https://github.com/rust-lang/reference
Revert #1423: Document C string literal tokens.
This reverts commit21a27e1689
, reversing changes made to01a12f22be
. This is being reverted in https://github.com/rust-lang/rust/pull/119528
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@ -8,8 +8,6 @@
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> | [BYTE_LITERAL]\
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> | [BYTE_STRING_LITERAL]\
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> | [RAW_BYTE_STRING_LITERAL]\
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> | [C_STRING_LITERAL]\
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> | [RAW_C_STRING_LITERAL]\
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> | [INTEGER_LITERAL]\
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> | [FLOAT_LITERAL]\
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> | `true` | `false`
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@ -50,12 +48,6 @@ A string literal expression consists of a single [BYTE_STRING_LITERAL] or [RAW_B
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> **Note**: This section is incomplete.
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## C string literal expressions
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A C string literal expression consists of a single [C_STRING_LITERAL] or [RAW_C_STRING_LITERAL] token.
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> **Note**: This section is incomplete.
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## Integer literal expressions
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An integer literal expression consists of a single [INTEGER_LITERAL] token.
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@ -190,7 +182,5 @@ The expression's type is the primitive [boolean type], and its value is:
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[BYTE_LITERAL]: ../tokens.md#byte-literals
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[BYTE_STRING_LITERAL]: ../tokens.md#byte-string-literals
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[RAW_BYTE_STRING_LITERAL]: ../tokens.md#raw-byte-string-literals
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[C_STRING_LITERAL]: ../tokens.md#c-string-literals
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[RAW_C_STRING_LITERAL]: ../tokens.md#raw-c-string-literals
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[INTEGER_LITERAL]: ../tokens.md#integer-literals
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[FLOAT_LITERAL]: ../tokens.md#floating-point-literals
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@ -123,8 +123,6 @@ if let (a, 3) = (1, 2) { // "(a, 3)" is refutable, and will not match
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> | [RAW_STRING_LITERAL]\
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> | [BYTE_STRING_LITERAL]\
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> | [RAW_BYTE_STRING_LITERAL]\
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> | [C_STRING_LITERAL]\
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> | [RAW_C_STRING_LITERAL]\
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> | `-`<sup>?</sup> [INTEGER_LITERAL]\
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> | `-`<sup>?</sup> [FLOAT_LITERAL]
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@ -134,8 +132,6 @@ if let (a, 3) = (1, 2) { // "(a, 3)" is refutable, and will not match
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[RAW_STRING_LITERAL]: tokens.md#raw-string-literals
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[BYTE_STRING_LITERAL]: tokens.md#byte-string-literals
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[RAW_BYTE_STRING_LITERAL]: tokens.md#raw-byte-string-literals
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[C_STRING_LITERAL]: tokens.md#c-string-literals
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[RAW_C_STRING_LITERAL]: tokens.md#raw-c-string-literals
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[INTEGER_LITERAL]: tokens.md#integer-literals
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[FLOAT_LITERAL]: tokens.md#floating-point-literals
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@ -148,14 +144,6 @@ Floating-point literals are currently accepted, but due to the complexity of com
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</div>
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<div class="warning">
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C string and raw C string literals are accepted in literal patterns, but `&CStr`
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doesn't implement structural equality (`#[derive(Eq, PartialEq)]`) and therefore
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any such `match` on a `&CStr` will be rejected with a type error.
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</div>
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Literal patterns are always refutable.
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Examples:
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109
src/tokens.md
109
src/tokens.md
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@ -32,8 +32,6 @@ Literals are tokens used in [literal expressions].
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| [Byte](#byte-literals) | `b'H'` | 0 | All ASCII | [Quote](#quote-escapes) & [Byte](#byte-escapes) |
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| [Byte string](#byte-string-literals) | `b"hello"` | 0 | All ASCII | [Quote](#quote-escapes) & [Byte](#byte-escapes) |
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| [Raw byte string](#raw-byte-string-literals) | `br#"hello"#` | <256 | All ASCII | `N/A` |
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| [C string](#c-string-literals) | `c"hello"` | 0 | All Unicode | [Quote](#quote-escapes) & [Byte](#byte-escapes) & [Unicode](#unicode-escapes) |
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| [Raw C string](#raw-c-string-literals) | `cr#"hello"#` | <256 | All Unicode | `N/A` |
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\* The number of `#`s on each side of the same literal must be equivalent.
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@ -330,107 +328,6 @@ b"\x52"; b"R"; br"R"; // R
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b"\\x52"; br"\x52"; // \x52
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```
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### C string and raw C string literals
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#### C string literals
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> **<sup>Lexer</sup>**\
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> C_STRING_LITERAL :\
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> `c"` (\
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> ~\[`"` `\` _IsolatedCR_]\
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> | BYTE_ESCAPE\
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> | UNICODE_ESCAPE\
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> | STRING_CONTINUE\
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> )<sup>\*</sup> `"` SUFFIX<sup>?</sup>
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A _C string literal_ is a sequence of Unicode characters and _escapes_,
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preceded by the characters `U+0063` (`c`) and `U+0022` (double-quote), and
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followed by the character `U+0022`. If the character `U+0022` is present within
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the literal, it must be _escaped_ by a preceding `U+005C` (`\`) character.
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Alternatively, a C string literal can be a _raw C string literal_, defined
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below. The type of a C string literal is [`&core::ffi::CStr`][CStr].
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[CStr]: ../core/ffi/struct.CStr.html
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C strings are implicitly terminated by byte `0x00`, so the C string literal
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`c""` is equivalent to manually constructing a `&CStr` from the byte string
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literal `b"\x00"`. Other than the implicit terminator, byte `0x00` is not
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permitted within a C string.
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Some additional _escapes_ are available in non-raw C string literals. An escape
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starts with a `U+005C` (`\`) and continues with one of the following forms:
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* A _byte escape_ escape starts with `U+0078` (`x`) and is followed by exactly
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two _hex digits_. It denotes the byte equal to the provided hex value.
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* A _24-bit code point escape_ starts with `U+0075` (`u`) and is followed
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by up to six _hex digits_ surrounded by braces `U+007B` (`{`) and `U+007D`
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(`}`). It denotes the Unicode code point equal to the provided hex value,
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encoded as UTF-8.
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* A _whitespace escape_ is one of the characters `U+006E` (`n`), `U+0072`
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(`r`), or `U+0074` (`t`), denoting the bytes values `0x0A` (ASCII LF),
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`0x0D` (ASCII CR) or `0x09` (ASCII HT) respectively.
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* The _backslash escape_ is the character `U+005C` (`\`) which must be
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escaped in order to denote its ASCII encoding `0x5C`.
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The escape sequences `\0`, `\x00`, and `\u{0000}` are permitted within the token
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but will be rejected as invalid, as C strings may not contain byte `0x00` except
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as the implicit terminator.
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A C string represents bytes with no defined encoding, but a C string literal
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may contain Unicode characters above `U+007F`. Such characters will be replaced
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with the bytes of that character's UTF-8 representation.
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The following C string literals are equivalent:
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```rust
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c"æ"; // LATIN SMALL LETTER AE (U+00E6)
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c"\u{00E6}";
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c"\xC3\xA6";
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```
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> **Edition Differences**: C string literals are accepted in the 2021 edition or
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> later. In earlier additions the token `c""` is lexed as `c ""`.
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#### Raw C string literals
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> **<sup>Lexer</sup>**\
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> RAW_C_STRING_LITERAL :\
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> `cr` RAW_C_STRING_CONTENT SUFFIX<sup>?</sup>
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>
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> RAW_C_STRING_CONTENT :\
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> `"` ( ~ _IsolatedCR_ )<sup>* (non-greedy)</sup> `"`\
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> | `#` RAW_C_STRING_CONTENT `#`
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Raw C string literals do not process any escapes. They start with the
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character `U+0063` (`c`), followed by `U+0072` (`r`), followed by fewer than 256
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of the character `U+0023` (`#`), and a `U+0022` (double-quote) character. The
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_raw C string body_ can contain any sequence of Unicode characters and is
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terminated only by another `U+0022` (double-quote) character, followed by the
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same number of `U+0023` (`#`) characters that preceded the opening `U+0022`
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(double-quote) character.
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All characters contained in the raw C string body represent themselves in UTF-8
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encoding. The characters `U+0022` (double-quote) (except when followed by at
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least as many `U+0023` (`#`) characters as were used to start the raw C string
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literal) or `U+005C` (`\`) do not have any special meaning.
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> **Edition Differences**: Raw C string literals are accepted in the 2021
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> edition or later. In earlier additions the token `cr""` is lexed as `cr ""`,
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> and `cr#""#` is lexed as `cr #""#` (which is non-grammatical).
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#### Examples for C string and raw C string literals
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```rust
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c"foo"; cr"foo"; // foo
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c"\"foo\""; cr#""foo""#; // "foo"
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c"foo #\"# bar";
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cr##"foo #"# bar"##; // foo #"# bar
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c"\x52"; c"R"; cr"R"; // R
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c"\\x52"; cr"\x52"; // \x52
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```
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### Number literals
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A _number literal_ is either an _integer literal_ or a _floating-point
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## Reserved prefixes
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> **<sup>Lexer 2021+</sup>**\
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> RESERVED_TOKEN_DOUBLE_QUOTE : ( IDENTIFIER_OR_KEYWORD <sub>_Except `b` or `c` or `r` or `br` or `cr`_</sub> | `_` ) `"`\
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> RESERVED_TOKEN_DOUBLE_QUOTE : ( IDENTIFIER_OR_KEYWORD <sub>_Except `b` or `r` or `br`_</sub> | `_` ) `"`\
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> RESERVED_TOKEN_SINGLE_QUOTE : ( IDENTIFIER_OR_KEYWORD <sub>_Except `b`_</sub> | `_` ) `'`\
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> RESERVED_TOKEN_POUND : ( IDENTIFIER_OR_KEYWORD <sub>_Except `r` or `br` or `cr`_</sub> | `_` ) `#`
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> RESERVED_TOKEN_POUND : ( IDENTIFIER_OR_KEYWORD <sub>_Except `r` or `br`_</sub> | `_` ) `#`
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Some lexical forms known as _reserved prefixes_ are reserved for future use.
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Note that raw identifiers, raw string literals, and raw byte string literals may contain a `#` character but are not interpreted as containing a reserved prefix.
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Similarly the `r`, `b`, `br`, `c`, and `cr` prefixes used in raw string literals, byte literals, byte string literals, raw byte string literals, C string literals, and raw C string literals are not interpreted as reserved prefixes.
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Similarly the `r`, `b`, and `br` prefixes used in raw string literals, byte literals, byte string literals, and raw byte string literals are not interpreted as reserved prefixes.
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> **Edition Differences**: Starting with the 2021 edition, reserved prefixes are reported as an error by the lexer (in particular, they cannot be passed to macros).
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>
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