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Document valid values of the char type #93493

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Feb 2, 2022
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Document valid values of the char type #93493

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4d4ec97
Document char validity
GKFX Jan 30, 2022
5357ec1
(#93493) Add items from code review
GKFX Jan 31, 2022
d372baf
Fix annotation of code blocks
GKFX Feb 1, 2022
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38 changes: 33 additions & 5 deletions library/core/src/primitive_docs.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -279,16 +279,44 @@ mod prim_never {}
///
/// The `char` type represents a single character. More specifically, since
/// 'character' isn't a well-defined concept in Unicode, `char` is a '[Unicode
/// scalar value]', which is similar to, but not the same as, a '[Unicode code
/// point]'.
///
/// [Unicode scalar value]: https://www.unicode.org/glossary/#unicode_scalar_value
/// [Unicode code point]: https://www.unicode.org/glossary/#code_point
/// scalar value]'.
///
/// This documentation describes a number of methods and trait implementations on the
/// `char` type. For technical reasons, there is additional, separate
/// documentation in [the `std::char` module](char/index.html) as well.
///
/// # Validity
///
/// A `char` is a '[Unicode scalar value]', which is any '[Unicode code point]'
/// other than a [surrogate code point]. This has a fixed numerical definition:
/// code points are in the range `'\0'` to `char::MAX` (`'\u{10FFFF}'`), inclusive.
/// Surrogate code points, used by UTF-16, are in the range U+D800 to U+DFFF.
///
/// No `char` may be constructed, whether as a literal or at runtime, that is not a
/// Unicode scalar value:
///
/// ```text
/// let forbidden_chars = [
/// // Each of these is a compiler error
/// '\u{D800}', '\u{DFFF}', '\u{110000}',
///
/// // Panics; from_u32 returns None.
/// char::from_u32(0xDE01).unwrap(),
///
/// // Undefined behaviour
/// unsafe { char::from_u32_unchecked(0x110000) },
/// ];
/// ```
///
/// Unicode is regularly updated. Many USVs are not currently assigned to a
/// character, but may be in the future ("reserved"); some will never be a character
/// ("noncharacters"); and some may be given different meanings by different users
/// ("private use").
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I'm not sure about the wording of this paragraph. If I didn't know otherwise, I might assume from the context that "reserved", "noncharacters" and "private use" were also currently invalid for char (but may become valid later).

///
/// [Unicode scalar value]: https://www.unicode.org/glossary/#unicode_scalar_value
/// [Unicode code point]: https://www.unicode.org/glossary/#code_point
/// [surrogate code point]: https://www.unicode.org/glossary/#surrogate_code_point
///
/// # Representation
///
/// `char` is always four bytes in size. This is a different representation than
Expand Down
38 changes: 33 additions & 5 deletions library/std/src/primitive_docs.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -279,16 +279,44 @@ mod prim_never {}
///
/// The `char` type represents a single character. More specifically, since
/// 'character' isn't a well-defined concept in Unicode, `char` is a '[Unicode
/// scalar value]', which is similar to, but not the same as, a '[Unicode code
/// point]'.
///
/// [Unicode scalar value]: https://www.unicode.org/glossary/#unicode_scalar_value
/// [Unicode code point]: https://www.unicode.org/glossary/#code_point
/// scalar value]'.
///
/// This documentation describes a number of methods and trait implementations on the
/// `char` type. For technical reasons, there is additional, separate
/// documentation in [the `std::char` module](char/index.html) as well.
///
/// # Validity
///
/// A `char` is a '[Unicode scalar value]', which is any '[Unicode code point]'
/// other than a [surrogate code point]. This has a fixed numerical definition:
/// code points are in the range `'\0'` to `char::MAX` (`'\u{10FFFF}'`), inclusive.
/// Surrogate code points, used by UTF-16, are in the range U+D800 to U+DFFF.
///
/// No `char` may be constructed, whether as a literal or at runtime, that is not a
/// Unicode scalar value:
///
/// ```text
/// let forbidden_chars = [
/// // Each of these is a compiler error
/// '\u{D800}', '\u{DFFF}', '\u{110000}',
///
/// // Panics; from_u32 returns None.
/// char::from_u32(0xDE01).unwrap(),
///
/// // Undefined behaviour
/// unsafe { char::from_u32_unchecked(0x110000) },
/// ];
/// ```
///
/// Unicode is regularly updated. Many USVs are not currently assigned to a
/// character, but may be in the future ("reserved"); some will never be a character
/// ("noncharacters"); and some may be given different meanings by different users
/// ("private use").
///
/// [Unicode scalar value]: https://www.unicode.org/glossary/#unicode_scalar_value
/// [Unicode code point]: https://www.unicode.org/glossary/#code_point
/// [surrogate code point]: https://www.unicode.org/glossary/#surrogate_code_point
///
/// # Representation
///
/// `char` is always four bytes in size. This is a different representation than
Expand Down