Char Methods Rust

https://github.com/rust-lang/rust/blob/master/library/core/src/char/methods.rs
Lars3 years ago1 file
char-methods.rs
//! impl char {}

use crate::slice;
use crate::str::from_utf8_unchecked_mut;
use crate::unicode::printable::is_printable;
use crate::unicode::{self, conversions};

use super::*;

impl char {
    /// The lowest valid code point a `char` can have, `'\0'`.
    ///
    /// Unlike integer types, `char` actually has a gap in the middle,
    /// meaning that the range of possible `char`s is smaller than you
    /// might expect. Ranges of `char` will automatically hop this gap
    /// for you:
    ///
    /// ```
    /// #![feature(char_min)]
    /// let dist = u32::from(char::MAX) - u32::from(char::MIN);
    /// let size = (char::MIN..=char::MAX).count() as u32;
    /// assert!(size < dist);
    /// ```
    ///
    /// Despite this gap, the `MIN` and [`MAX`] values can be used as bounds for
    /// all `char` values.
    ///
    /// [`MAX`]: char::MAX
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(char_min)]
    /// # fn something_which_returns_char() -> char { 'a' }
    /// let c: char = something_which_returns_char();
    /// assert!(char::MIN <= c);
    ///
    /// let value_at_min = u32::from(char::MIN);
    /// assert_eq!(char::from_u32(value_at_min), Some('\0'));
    /// ```
    #[unstable(feature = "char_min", issue = "114298")]
    pub const MIN: char = '\0';

    /// The highest valid code point a `char` can have, `'\u{10FFFF}'`.
    ///
    /// Unlike integer types, `char` actually has a gap in the middle,
    /// meaning that the range of possible `char`s is smaller than you
    /// might expect. Ranges of `char` will automatically hop this gap
    /// for you:
    ///
    /// ```
    /// #![feature(char_min)]
    /// let dist = u32::from(char::MAX) - u32::from(char::MIN);
    /// let size = (char::MIN..=char::MAX).count() as u32;
    /// assert!(size < dist);
    /// ```
    ///
    /// Despite this gap, the [`MIN`] and `MAX` values can be used as bounds for
    /// all `char` values.
    ///
    /// [`MIN`]: char::MIN
    ///
    /// # Examples
    ///
    /// ```
    /// # fn something_which_returns_char() -> char { 'a' }
    /// let c: char = something_which_returns_char();
    /// assert!(c <= char::MAX);
    ///
    /// let value_at_max = u32::from(char::MAX);
    /// assert_eq!(char::from_u32(value_at_max), Some('\u{10FFFF}'));
    /// assert_eq!(char::from_u32(value_at_max + 1), None);
    /// ```
    #[stable(feature = "assoc_char_consts", since = "1.52.0")]
    pub const MAX: char = '\u{10ffff}';

    /// `U+FFFD REPLACEMENT CHARACTER` (�) is used in Unicode to represent a
    /// decoding error.
    ///
    /// It can occur, for example, when giving ill-formed UTF-8 bytes to
    /// [`String::from_utf8_lossy`](../std/string/struct.String.html#method.from_utf8_lossy).
    #[stable(feature = "assoc_char_consts", since = "1.52.0")]
    pub const REPLACEMENT_CHARACTER: char = '\u{FFFD}';

    /// The version of [Unicode](https://www.unicode.org/) that the Unicode parts of
    /// `char` and `str` methods are based on.
    ///
    /// New versions of Unicode are released regularly and subsequently all methods
    /// in the standard library depending on Unicode are updated. Therefore the
    /// behavior of some `char` and `str` methods and the value of this constant
    /// changes over time. This is *not* considered to be a breaking change.
    ///
    /// The version numbering scheme is explained in
    /// [Unicode 11.0 or later, Section 3.1 Versions of the Unicode Standard](https://www.unicode.org/versions/Unicode11.0.0/ch03.pdf#page=4).
    #[stable(feature = "assoc_char_consts", since = "1.52.0")]
    pub const UNICODE_VERSION: (u8, u8, u8) = crate::unicode::UNICODE_VERSION;

    /// Creates an iterator over the UTF-16 encoded code points in `iter`,
    /// returning unpaired surrogates as `Err`s.
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// // 𝄞mus<invalid>ic<invalid>
    /// let v = [
    ///     0xD834, 0xDD1E, 0x006d, 0x0075, 0x0073, 0xDD1E, 0x0069, 0x0063, 0xD834,
    /// ];
    ///
    /// assert_eq!(
    ///     char::decode_utf16(v)
    ///         .map(|r| r.map_err(|e| e.unpaired_surrogate()))
    ///         .collect::<Vec<_>>(),
    ///     vec![
    ///         Ok('𝄞'),
    ///         Ok('m'), Ok('u'), Ok('s'),
    ///         Err(0xDD1E),
    ///         Ok('i'), Ok('c'),
    ///         Err(0xD834)
    ///     ]
    /// );
    /// ```
    ///
    /// A lossy decoder can be obtained by replacing `Err` results with the replacement character:
    ///
    /// ```
    /// // 𝄞mus<invalid>ic<invalid>
    /// let v = [
    ///     0xD834, 0xDD1E, 0x006d, 0x0075, 0x0073, 0xDD1E, 0x0069, 0x0063, 0xD834,
    /// ];
    ///
    /// assert_eq!(
    ///     char::decode_utf16(v)
    ///        .map(|r| r.unwrap_or(char::REPLACEMENT_CHARACTER))
    ///        .collect::<String>(),
    ///     "𝄞mus�ic�"
    /// );
    /// ```
    #[stable(feature = "assoc_char_funcs", since = "1.52.0")]
    #[inline]
    pub fn decode_utf16<I: IntoIterator<Item = u16>>(iter: I) -> DecodeUtf16<I::IntoIter> {
        super::decode::decode_utf16(iter)
    }

    /// Converts a `u32` to a `char`.
    ///
    /// Note that all `char`s are valid [`u32`]s, and can be cast to one with
    /// [`as`](../std/keyword.as.html):
    ///
    /// ```
    /// let c = '💯';
    /// let i = c as u32;
    ///
    /// assert_eq!(128175, i);
    /// ```
    ///
    /// However, the reverse is not true: not all valid [`u32`]s are valid
    /// `char`s. `from_u32()` will return `None` if the input is not a valid value
    /// for a `char`.
    ///
    /// For an unsafe version of this function which ignores these checks, see
    /// [`from_u32_unchecked`].
    ///
    /// [`from_u32_unchecked`]: #method.from_u32_unchecked
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// let c = char::from_u32(0x2764);
    ///
    /// assert_eq!(Some('❤'), c);
    /// ```
    ///
    /// Returning `None` when the input is not a valid `char`:
    ///
    /// ```
    /// let c = char::from_u32(0x110000);
    ///
    /// assert_eq!(None, c);
    /// ```
    #[stable(feature = "assoc_char_funcs", since = "1.52.0")]
    #[rustc_const_stable(feature = "const_char_convert", since = "1.67.0")]
    #[must_use]
    #[inline]
    pub const fn from_u32(i: u32) -> Option<char> {
        super::convert::from_u32(i)
    }

    /// Converts a `u32` to a `char`, ignoring validity.
    ///
    /// Note that all `char`s are valid [`u32`]s, and can be cast to one with
    /// `as`:
    ///
    /// ```
    /// let c = '💯';
    /// let i = c as u32;
    ///
    /// assert_eq!(128175, i);
    /// ```
    ///
    /// However, the reverse is not true: not all valid [`u32`]s are valid
    /// `char`s. `from_u32_unchecked()` will ignore this, and blindly cast to
    /// `char`, possibly creating an invalid one.
    ///
    /// # Safety
    ///
    /// This function is unsafe, as it may construct invalid `char` values.
    ///
    /// For a safe version of this function, see the [`from_u32`] function.
    ///
    /// [`from_u32`]: #method.from_u32
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// let c = unsafe { char::from_u32_unchecked(0x2764) };
    ///
    /// assert_eq!('❤', c);
    /// ```
    #[stable(feature = "assoc_char_funcs", since = "1.52.0")]
    #[rustc_const_unstable(feature = "const_char_from_u32_unchecked", issue = "89259")]
    #[must_use]
    #[inline]
    pub const unsafe fn from_u32_unchecked(i: u32) -> char {
        // SAFETY: the safety contract must be upheld by the caller.
        unsafe { super::convert::from_u32_unchecked(i) }
    }

    /// Converts a digit in the given radix to a `char`.
    ///
    /// A 'radix' here is sometimes also called a 'base'. A radix of two
    /// indicates a binary number, a radix of ten, decimal, and a radix of
    /// sixteen, hexadecimal, to give some common values. Arbitrary
    /// radices are supported.
    ///
    /// `from_digit()` will return `None` if the input is not a digit in
    /// the given radix.
    ///
    /// # Panics
    ///
    /// Panics if given a radix larger than 36.
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// let c = char::from_digit(4, 10);
    ///
    /// assert_eq!(Some('4'), c);
    ///
    /// // Decimal 11 is a single digit in base 16
    /// let c = char::from_digit(11, 16);
    ///
    /// assert_eq!(Some('b'), c);
    /// ```
    ///
    /// Returning `None` when the input is not a digit:
    ///
    /// ```
    /// let c = char::from_digit(20, 10);
    ///
    /// assert_eq!(None, c);
    /// ```
    ///
    /// Passing a large radix, causing a panic:
    ///
    /// ```should_panic
    /// // this panics
    /// let _c = char::from_digit(1, 37);
    /// ```
    #[stable(feature = "assoc_char_funcs", since = "1.52.0")]
    #[rustc_const_stable(feature = "const_char_convert", since = "1.67.0")]
    #[must_use]
    #[inline]
    pub const fn from_digit(num: u32, radix: u32) -> Option<char> {
        super::convert::from_digit(num, radix)
    }

    /// Checks if a `char` is a digit in the given radix.
    ///
    /// A 'radix' here is sometimes also called a 'base'. A radix of two
    /// indicates a binary number, a radix of ten, decimal, and a radix of
    /// sixteen, hexadecimal, to give some common values. Arbitrary
    /// radices are supported.
    ///
    /// Compared to [`is_numeric()`], this function only recognizes the characters
    /// `0-9`, `a-z` and `A-Z`.
    ///
    /// 'Digit' is defined to be only the following characters:
    ///
    /// * `0-9`
    /// * `a-z`
    /// * `A-Z`
    ///
    /// For a more comprehensive understanding of 'digit', see [`is_numeric()`].
    ///
    /// [`is_numeric()`]: #method.is_numeric
    ///
    /// # Panics
    ///
    /// Panics if given a radix larger than 36.
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// assert!('1'.is_digit(10));
    /// assert!('f'.is_digit(16));
    /// assert!(!'f'.is_digit(10));
    /// ```
    ///
    /// Passing a large radix, causing a panic:
    ///
    /// ```should_panic
    /// // this panics
    /// '1'.is_digit(37);
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[inline]
    pub fn is_digit(self, radix: u32) -> bool {
        self.to_digit(radix).is_some()
    }

    /// Converts a `char` to a digit in the given radix.
    ///
    /// A 'radix' here is sometimes also called a 'base'. A radix of two
    /// indicates a binary number, a radix of ten, decimal, and a radix of
    /// sixteen, hexadecimal, to give some common values. Arbitrary
    /// radices are supported.
    ///
    /// 'Digit' is defined to be only the following characters:
    ///
    /// * `0-9`
    /// * `a-z`
    /// * `A-Z`
    ///
    /// # Errors
    ///
    /// Returns `None` if the `char` does not refer to a digit in the given radix.
    ///
    /// # Panics
    ///
    /// Panics if given a radix larger than 36.
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// assert_eq!('1'.to_digit(10), Some(1));
    /// assert_eq!('f'.to_digit(16), Some(15));
    /// ```
    ///
    /// Passing a non-digit results in failure:
    ///
    /// ```
    /// assert_eq!('f'.to_digit(10), None);
    /// assert_eq!('z'.to_digit(16), None);
    /// ```
    ///
    /// Passing a large radix, causing a panic:
    ///
    /// ```should_panic
    /// // this panics
    /// let _ = '1'.to_digit(37);
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_const_stable(feature = "const_char_convert", since = "1.67.0")]
    #[must_use = "this returns the result of the operation, \
                  without modifying the original"]
    #[inline]
    pub const fn to_digit(self, radix: u32) -> Option<u32> {
        // If not a digit, a number greater than radix will be created.
        let mut digit = (self as u32).wrapping_sub('0' as u32);
        if radix > 10 {
            assert!(radix <= 36, "to_digit: radix is too high (maximum 36)");
            if digit < 10 {
                return Some(digit);
            }
            // Force the 6th bit to be set to ensure ascii is lower case.
            digit = (self as u32 | 0b10_0000).wrapping_sub('a' as u32).saturating_add(10);
        }
        // FIXME: once then_some is const fn, use it here
        if digit < radix { Some(digit) } else { None }
    }

    /// Returns an iterator that yields the hexadecimal Unicode escape of a
    /// character as `char`s.
    ///
    /// This will escape characters with the Rust syntax of the form
    /// `\u{NNNNNN}` where `NNNNNN` is a hexadecimal representation.
    ///
    /// # Examples
    ///
    /// As an iterator:
    ///
    /// ```
    /// for c in '❤'.escape_unicode() {
    ///     print!("{c}");
    /// }
    /// println!();
    /// ```
    ///
    /// Using `println!` directly:
    ///
    /// ```
    /// println!("{}", '❤'.escape_unicode());
    /// ```
    ///
    /// Both are equivalent to:
    ///
    /// ```
    /// println!("\\u{{2764}}");
    /// ```
    ///
    /// Using [`to_string`](../std/string/trait.ToString.html#tymethod.to_string):
    ///
    /// ```
    /// assert_eq!('❤'.escape_unicode().to_string(), "\\u{2764}");
    /// ```
    #[must_use = "this returns the escaped char as an iterator, \
                  without modifying the original"]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[inline]
    pub fn escape_unicode(self) -> EscapeUnicode {
        EscapeUnicode::new(self)
    }

    /// An extended version of `escape_debug` that optionally permits escaping
    /// Extended Grapheme codepoints, single quotes, and double quotes. This
    /// allows us to format characters like nonspacing marks better when they're
    /// at the start of a string, and allows escaping single quotes in
    /// characters, and double quotes in strings.
    #[inline]
    pub(crate) fn escape_debug_ext(self, args: EscapeDebugExtArgs) -> EscapeDebug {
        match self {
            '\0' => EscapeDebug::backslash(ascii::Char::Digit0),
            '\t' => EscapeDebug::backslash(ascii::Char::SmallT),
            '\r' => EscapeDebug::backslash(ascii::Char::SmallR),
            '\n' => EscapeDebug::backslash(ascii::Char::SmallN),
            '\\' => EscapeDebug::backslash(ascii::Char::ReverseSolidus),
            '\"' if args.escape_double_quote => EscapeDebug::backslash(ascii::Char::QuotationMark),
            '\'' if args.escape_single_quote => EscapeDebug::backslash(ascii::Char::Apostrophe),
            _ if args.escape_grapheme_extended && self.is_grapheme_extended() => {
                EscapeDebug::from_unicode(self.escape_unicode())
            }
            _ if is_printable(self) => EscapeDebug::printable(self),
            _ => EscapeDebug::from_unicode(self.escape_unicode()),
        }
    }

    /// Returns an iterator that yields the literal escape code of a character
    /// as `char`s.
    ///
    /// This will escape the characters similar to the [`Debug`](core::fmt::Debug) implementations
    /// of `str` or `char`.
    ///
    /// # Examples
    ///
    /// As an iterator:
    ///
    /// ```
    /// for c in '\n'.escape_debug() {
    ///     print!("{c}");
    /// }
    /// println!();
    /// ```
    ///
    /// Using `println!` directly:
    ///
    /// ```
    /// println!("{}", '\n'.escape_debug());
    /// ```
    ///
    /// Both are equivalent to:
    ///
    /// ```
    /// println!("\\n");
    /// ```
    ///
    /// Using [`to_string`](../std/string/trait.ToString.html#tymethod.to_string):
    ///
    /// ```
    /// assert_eq!('\n'.escape_debug().to_string(), "\\n");
    /// ```
    #[must_use = "this returns the escaped char as an iterator, \
                  without modifying the original"]
    #[stable(feature = "char_escape_debug", since = "1.20.0")]
    #[inline]
    pub fn escape_debug(self) -> EscapeDebug {
        self.escape_debug_ext(EscapeDebugExtArgs::ESCAPE_ALL)
    }

    /// Returns an iterator that yields the literal escape code of a character
    /// as `char`s.
    ///
    /// The default is chosen with a bias toward producing literals that are
    /// legal in a variety of languages, including C++11 and similar C-family
    /// languages. The exact rules are:
    ///
    /// * Tab is escaped as `\t`.
    /// * Carriage return is escaped as `\r`.
    /// * Line feed is escaped as `\n`.
    /// * Single quote is escaped as `\'`.
    /// * Double quote is escaped as `\"`.
    /// * Backslash is escaped as `\\`.
    /// * Any character in the 'printable ASCII' range `0x20` .. `0x7e`
    ///   inclusive is not escaped.
    /// * All other characters are given hexadecimal Unicode escapes; see
    ///   [`escape_unicode`].
    ///
    /// [`escape_unicode`]: #method.escape_unicode
    ///
    /// # Examples
    ///
    /// As an iterator:
    ///
    /// ```
    /// for c in '"'.escape_default() {
    ///     print!("{c}");
    /// }
    /// println!();
    /// ```
    ///
    /// Using `println!` directly:
    ///
    /// ```
    /// println!("{}", '"'.escape_default());
    /// ```
    ///
    /// Both are equivalent to:
    ///
    /// ```
    /// println!("\\\"");
    /// ```
    ///
    /// Using [`to_string`](../std/string/trait.ToString.html#tymethod.to_string):
    ///
    /// ```
    /// assert_eq!('"'.escape_default().to_string(), "\\\"");
    /// ```
    #[must_use = "this returns the escaped char as an iterator, \
                  without modifying the original"]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[inline]
    pub fn escape_default(self) -> EscapeDefault {
        match self {
            '\t' => EscapeDefault::backslash(ascii::Char::SmallT),
            '\r' => EscapeDefault::backslash(ascii::Char::SmallR),
            '\n' => EscapeDefault::backslash(ascii::Char::SmallN),
            '\\' | '\'' | '"' => EscapeDefault::backslash(self.as_ascii().unwrap()),
            '\x20'..='\x7e' => EscapeDefault::printable(self.as_ascii().unwrap()),
            _ => EscapeDefault::from_unicode(self.escape_unicode()),
        }
    }

    /// Returns the number of bytes this `char` would need if encoded in UTF-8.
    ///
    /// That number of bytes is always between 1 and 4, inclusive.
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// let len = 'A'.len_utf8();
    /// assert_eq!(len, 1);
    ///
    /// let len = 'ß'.len_utf8();
    /// assert_eq!(len, 2);
    ///
    /// let len = 'ℝ'.len_utf8();
    /// assert_eq!(len, 3);
    ///
    /// let len = '💣'.len_utf8();
    /// assert_eq!(len, 4);
    /// ```
    ///
    /// The `&str` type guarantees that its contents are UTF-8, and so we can compare the length it
    /// would take if each code point was represented as a `char` vs in the `&str` itself:
    ///
    /// ```
    /// // as chars
    /// let eastern = '東';
    /// let capital = '京';
    ///
    /// // both can be represented as three bytes
    /// assert_eq!(3, eastern.len_utf8());
    /// assert_eq!(3, capital.len_utf8());
    ///
    /// // as a &str, these two are encoded in UTF-8
    /// let tokyo = "東京";
    ///
    /// let len = eastern.len_utf8() + capital.len_utf8();
    ///
    /// // we can see that they take six bytes total...
    /// assert_eq!(6, tokyo.len());
    ///
    /// // ... just like the &str
    /// assert_eq!(len, tokyo.len());
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_const_stable(feature = "const_char_len_utf", since = "1.52.0")]
    #[inline]
    pub const fn len_utf8(self) -> usize {
        len_utf8(self as u32)
    }

    /// Returns the number of 16-bit code units this `char` would need if
    /// encoded in UTF-16.
    ///
    /// That number of code units is always either 1 or 2, for unicode scalar values in
    /// the [basic multilingual plane] or [supplementary planes] respectively.
    ///
    /// See the documentation for [`len_utf8()`] for more explanation of this
    /// concept. This function is a mirror, but for UTF-16 instead of UTF-8.
    ///
    /// [basic multilingual plane]: http://www.unicode.org/glossary/#basic_multilingual_plane
    /// [supplementary planes]: http://www.unicode.org/glossary/#supplementary_planes
    /// [`len_utf8()`]: #method.len_utf8
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// let n = 'ß'.len_utf16();
    /// assert_eq!(n, 1);
    ///
    /// let len = '💣'.len_utf16();
    /// assert_eq!(len, 2);
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_const_stable(feature = "const_char_len_utf", since = "1.52.0")]
    #[inline]
    pub const fn len_utf16(self) -> usize {
        let ch = self as u32;
        if (ch & 0xFFFF) == ch { 1 } else { 2 }
    }

    /// Encodes this character as UTF-8 into the provided byte buffer,
    /// and then returns the subslice of the buffer that contains the encoded character.
    ///
    /// # Panics
    ///
    /// Panics if the buffer is not large enough.
    /// A buffer of length four is large enough to encode any `char`.
    ///
    /// # Examples
    ///
    /// In both of these examples, 'ß' takes two bytes to encode.
    ///
    /// ```
    /// let mut b = [0; 2];
    ///
    /// let result = 'ß'.encode_utf8(&mut b);
    ///
    /// assert_eq!(result, "ß");
    ///
    /// assert_eq!(result.len(), 2);
    /// ```
    ///
    /// A buffer that's too small:
    ///
    /// ```should_panic
    /// let mut b = [0; 1];
    ///
    /// // this panics
    /// 'ß'.encode_utf8(&mut b);
    /// ```
    #[stable(feature = "unicode_encode_char", since = "1.15.0")]
    #[inline]
    pub fn encode_utf8(self, dst: &mut [u8]) -> &mut str {
        // SAFETY: `char` is not a surrogate, so this is valid UTF-8.
        unsafe { from_utf8_unchecked_mut(encode_utf8_raw(self as u32, dst)) }
    }

    /// Encodes this character as UTF-16 into the provided `u16` buffer,
    /// and then returns the subslice of the buffer that contains the encoded character.
    ///
    /// # Panics
    ///
    /// Panics if the buffer is not large enough.
    /// A buffer of length 2 is large enough to encode any `char`.
    ///
    /// # Examples
    ///
    /// In both of these examples, '𝕊' takes two `u16`s to encode.
    ///
    /// ```
    /// let mut b = [0; 2];
    ///
    /// let result = '𝕊'.encode_utf16(&mut b);
    ///
    /// assert_eq!(result.len(), 2);
    /// ```
    ///
    /// A buffer that's too small:
    ///
    /// ```should_panic
    /// let mut b = [0; 1];
    ///
    /// // this panics
    /// '𝕊'.encode_utf16(&mut b);
    /// ```
    #[stable(feature = "unicode_encode_char", since = "1.15.0")]
    #[inline]
    pub fn encode_utf16(self, dst: &mut [u16]) -> &mut [u16] {
        encode_utf16_raw(self as u32, dst)
    }

    /// Returns `true` if this `char` has the `Alphabetic` property.
    ///
    /// `Alphabetic` is described in Chapter 4 (Character Properties) of the [Unicode Standard] and
    /// specified in the [Unicode Character Database][ucd] [`DerivedCoreProperties.txt`].
    ///
    /// [Unicode Standard]: https://www.unicode.org/versions/latest/
    /// [ucd]: https://www.unicode.org/reports/tr44/
    /// [`DerivedCoreProperties.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/DerivedCoreProperties.txt
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// assert!('a'.is_alphabetic());
    /// assert!('京'.is_alphabetic());
    ///
    /// let c = '💝';
    /// // love is many things, but it is not alphabetic
    /// assert!(!c.is_alphabetic());
    /// ```
    #[must_use]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[inline]
    pub fn is_alphabetic(self) -> bool {
        match self {
            'a'..='z' | 'A'..='Z' => true,
            c => c > '\x7f' && unicode::Alphabetic(c),
        }
    }

    /// Returns `true` if this `char` has the `Lowercase` property.
    ///
    /// `Lowercase` is described in Chapter 4 (Character Properties) of the [Unicode Standard] and
    /// specified in the [Unicode Character Database][ucd] [`DerivedCoreProperties.txt`].
    ///
    /// [Unicode Standard]: https://www.unicode.org/versions/latest/
    /// [ucd]: https://www.unicode.org/reports/tr44/
    /// [`DerivedCoreProperties.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/DerivedCoreProperties.txt
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// assert!('a'.is_lowercase());
    /// assert!('δ'.is_lowercase());
    /// assert!(!'A'.is_lowercase());
    /// assert!(!'Δ'.is_lowercase());
    ///
    /// // The various Chinese scripts and punctuation do not have case, and so:
    /// assert!(!'中'.is_lowercase());
    /// assert!(!' '.is_lowercase());
    /// ```
    ///
    /// In a const context:
    ///
    /// ```
    /// #![feature(const_unicode_case_lookup)]
    /// const CAPITAL_DELTA_IS_LOWERCASE: bool = 'Δ'.is_lowercase();
    /// assert!(!CAPITAL_DELTA_IS_LOWERCASE);
    /// ```
    #[must_use]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_const_unstable(feature = "const_unicode_case_lookup", issue = "101400")]
    #[inline]
    pub const fn is_lowercase(self) -> bool {
        match self {
            'a'..='z' => true,
            c => c > '\x7f' && unicode::Lowercase(c),
        }
    }

    /// Returns `true` if this `char` has the `Uppercase` property.
    ///
    /// `Uppercase` is described in Chapter 4 (Character Properties) of the [Unicode Standard] and
    /// specified in the [Unicode Character Database][ucd] [`DerivedCoreProperties.txt`].
    ///
    /// [Unicode Standard]: https://www.unicode.org/versions/latest/
    /// [ucd]: https://www.unicode.org/reports/tr44/
    /// [`DerivedCoreProperties.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/DerivedCoreProperties.txt
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// assert!(!'a'.is_uppercase());
    /// assert!(!'δ'.is_uppercase());
    /// assert!('A'.is_uppercase());
    /// assert!('Δ'.is_uppercase());
    ///
    /// // The various Chinese scripts and punctuation do not have case, and so:
    /// assert!(!'中'.is_uppercase());
    /// assert!(!' '.is_uppercase());
    /// ```
    ///
    /// In a const context:
    ///
    /// ```
    /// #![feature(const_unicode_case_lookup)]
    /// const CAPITAL_DELTA_IS_UPPERCASE: bool = 'Δ'.is_uppercase();
    /// assert!(CAPITAL_DELTA_IS_UPPERCASE);
    /// ```
    #[must_use]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[rustc_const_unstable(feature = "const_unicode_case_lookup", issue = "101400")]
    #[inline]
    pub const fn is_uppercase(self) -> bool {
        match self {
            'A'..='Z' => true,
            c => c > '\x7f' && unicode::Uppercase(c),
        }
    }

    /// Returns `true` if this `char` has the `White_Space` property.
    ///
    /// `White_Space` is specified in the [Unicode Character Database][ucd] [`PropList.txt`].
    ///
    /// [ucd]: https://www.unicode.org/reports/tr44/
    /// [`PropList.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/PropList.txt
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// assert!(' '.is_whitespace());
    ///
    /// // line break
    /// assert!('\n'.is_whitespace());
    ///
    /// // a non-breaking space
    /// assert!('\u{A0}'.is_whitespace());
    ///
    /// assert!(!'越'.is_whitespace());
    /// ```
    #[must_use]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[inline]
    pub fn is_whitespace(self) -> bool {
        match self {
            ' ' | '\x09'..='\x0d' => true,
            c => c > '\x7f' && unicode::White_Space(c),
        }
    }

    /// Returns `true` if this `char` satisfies either [`is_alphabetic()`] or [`is_numeric()`].
    ///
    /// [`is_alphabetic()`]: #method.is_alphabetic
    /// [`is_numeric()`]: #method.is_numeric
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// assert!('٣'.is_alphanumeric());
    /// assert!('7'.is_alphanumeric());
    /// assert!('৬'.is_alphanumeric());
    /// assert!('¾'.is_alphanumeric());
    /// assert!('①'.is_alphanumeric());
    /// assert!('K'.is_alphanumeric());
    /// assert!('و'.is_alphanumeric());
    /// assert!('藏'.is_alphanumeric());
    /// ```
    #[must_use]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[inline]
    pub fn is_alphanumeric(self) -> bool {
        self.is_alphabetic() || self.is_numeric()
    }

    /// Returns `true` if this `char` has the general category for control codes.
    ///
    /// Control codes (code points with the general category of `Cc`) are described in Chapter 4
    /// (Character Properties) of the [Unicode Standard] and specified in the [Unicode Character
    /// Database][ucd] [`UnicodeData.txt`].
    ///
    /// [Unicode Standard]: https://www.unicode.org/versions/latest/
    /// [ucd]: https://www.unicode.org/reports/tr44/
    /// [`UnicodeData.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/UnicodeData.txt
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// // U+009C, STRING TERMINATOR
    /// assert!(''.is_control());
    /// assert!(!'q'.is_control());
    /// ```
    #[must_use]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[inline]
    pub fn is_control(self) -> bool {
        unicode::Cc(self)
    }

    /// Returns `true` if this `char` has the `Grapheme_Extend` property.
    ///
    /// `Grapheme_Extend` is described in [Unicode Standard Annex #29 (Unicode Text
    /// Segmentation)][uax29] and specified in the [Unicode Character Database][ucd]
    /// [`DerivedCoreProperties.txt`].
    ///
    /// [uax29]: https://www.unicode.org/reports/tr29/
    /// [ucd]: https://www.unicode.org/reports/tr44/
    /// [`DerivedCoreProperties.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/DerivedCoreProperties.txt
    #[must_use]
    #[inline]
    pub(crate) fn is_grapheme_extended(self) -> bool {
        unicode::Grapheme_Extend(self)
    }

    /// Returns `true` if this `char` has one of the general categories for numbers.
    ///
    /// The general categories for numbers (`Nd` for decimal digits, `Nl` for letter-like numeric
    /// characters, and `No` for other numeric characters) are specified in the [Unicode Character
    /// Database][ucd] [`UnicodeData.txt`].
    ///
    /// This method doesn't cover everything that could be considered a number, e.g. ideographic numbers like '三'.
    /// If you want everything including characters with overlapping purposes then you might want to use
    /// a unicode or language-processing library that exposes the appropriate character properties instead
    /// of looking at the unicode categories.
    ///
    /// If you want to parse ASCII decimal digits (0-9) or ASCII base-N, use
    /// `is_ascii_digit` or `is_digit` instead.
    ///
    /// [Unicode Standard]: https://www.unicode.org/versions/latest/
    /// [ucd]: https://www.unicode.org/reports/tr44/
    /// [`UnicodeData.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/UnicodeData.txt
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// assert!('٣'.is_numeric());
    /// assert!('7'.is_numeric());
    /// assert!('৬'.is_numeric());
    /// assert!('¾'.is_numeric());
    /// assert!('①'.is_numeric());
    /// assert!(!'K'.is_numeric());
    /// assert!(!'و'.is_numeric());
    /// assert!(!'藏'.is_numeric());
    /// assert!(!'三'.is_numeric());
    /// ```
    #[must_use]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[inline]
    pub fn is_numeric(self) -> bool {
        match self {
            '0'..='9' => true,
            c => c > '\x7f' && unicode::N(c),
        }
    }

    /// Returns an iterator that yields the lowercase mapping of this `char` as one or more
    /// `char`s.
    ///
    /// If this `char` does not have a lowercase mapping, the iterator yields the same `char`.
    ///
    /// If this `char` has a one-to-one lowercase mapping given by the [Unicode Character
    /// Database][ucd] [`UnicodeData.txt`], the iterator yields that `char`.
    ///
    /// [ucd]: https://www.unicode.org/reports/tr44/
    /// [`UnicodeData.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/UnicodeData.txt
    ///
    /// If this `char` requires special considerations (e.g. multiple `char`s) the iterator yields
    /// the `char`(s) given by [`SpecialCasing.txt`].
    ///
    /// [`SpecialCasing.txt`]: https://www.unicode.org/Public/UCD/latest/ucd/SpecialCasing.txt
    ///
    /// This operation performs an unconditional mapping without tailoring. That is, the conversion
    /// is independent of context and language.
    ///
    /// In the [Unicode Standard], Chapter 4 (Character Properties) discusses case mapping in
    /// general and Chapter 3 (Conformance) discusses the default algorithm for case conversion.
    ///
    /// [Unicode Standard]: https://www.unicode.org/versions/latest/
    ///
    /// # Examples
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