Move char conversions into a separate private module.

Author: SimonSapin

src/libcore/char/convert.rs

@@ -0,0 +1,304 @@
+// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Character conversions.
+
+use convert::TryFrom;
+use fmt;
+use mem::transmute;
+use str::FromStr;
+use super::MAX;
+
+/// Converts a `u32` to a `char`.
+///
+/// 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()` will return `None` if the input is not a valid value
+/// for a [`char`].
+///
+/// [`char`]: ../../std/primitive.char.html
+/// [`u32`]: ../../std/primitive.u32.html
+/// [`as`]: ../../book/first-edition/casting-between-types.html#as
+///
+/// For an unsafe version of this function which ignores these checks, see
+/// [`from_u32_unchecked`].
+///
+/// [`from_u32_unchecked`]: fn.from_u32_unchecked.html
+///
+/// # Examples
+///
+/// Basic usage:
+///
+/// ```
+/// use std::char;
+///
+/// let c = char::from_u32(0x2764);
+///
+/// assert_eq!(Some('❤'), c);
+/// ```
+///
+/// Returning `None` when the input is not a valid [`char`]:
+///
+/// ```
+/// use std::char;
+///
+/// let c = char::from_u32(0x110000);
+///
+/// assert_eq!(None, c);
+/// ```
+#[inline]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn from_u32(i: u32) -> Option<char> {
+    char::try_from(i).ok()
+}
+
+/// 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.
+///
+/// [`char`]: ../../std/primitive.char.html
+/// [`u32`]: ../../std/primitive.u32.html
+/// [`as`]: ../../book/first-edition/casting-between-types.html#as
+///
+/// # 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`]: fn.from_u32.html
+///
+/// # Examples
+///
+/// Basic usage:
+///
+/// ```
+/// use std::char;
+///
+/// let c = unsafe { char::from_u32_unchecked(0x2764) };
+///
+/// assert_eq!('❤', c);
+/// ```
+#[inline]
+#[stable(feature = "char_from_unchecked", since = "1.5.0")]
+pub unsafe fn from_u32_unchecked(i: u32) -> char {
+    transmute(i)
+}
+
+#[stable(feature = "char_convert", since = "1.13.0")]
+impl From<char> for u32 {
+    #[inline]
+    fn from(c: char) -> Self {
+        c as u32
+    }
+}
+
+/// Maps a byte in 0x00...0xFF to a `char` whose code point has the same value, in U+0000 to U+00FF.
+///
+/// Unicode is designed such that this effectively decodes bytes
+/// with the character encoding that IANA calls ISO-8859-1.
+/// This encoding is compatible with ASCII.
+///
+/// Note that this is different from ISO/IEC 8859-1 a.k.a. ISO 8859-1 (with one less hyphen),
+/// which leaves some "blanks", byte values that are not assigned to any character.
+/// ISO-8859-1 (the IANA one) assigns them to the C0 and C1 control codes.
+///
+/// Note that this is *also* different from Windows-1252 a.k.a. code page 1252,
+/// which is a superset ISO/IEC 8859-1 that assigns some (not all!) blanks
+/// to punctuation and various Latin characters.
+///
+/// To confuse things further, [on the Web](https://encoding.spec.whatwg.org/)
+/// `ascii`, `iso-8859-1`, and `windows-1252` are all aliases
+/// for a superset of Windows-1252 that fills the remaining blanks with corresponding
+/// C0 and C1 control codes.
+#[stable(feature = "char_convert", since = "1.13.0")]
+impl From<u8> for char {
+    #[inline]
+    fn from(i: u8) -> Self {
+        i as char
+    }
+}
+
+
+/// An error which can be returned when parsing a char.
+#[stable(feature = "char_from_str", since = "1.20.0")]
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct ParseCharError {
+    kind: CharErrorKind,
+}
+
+impl ParseCharError {
+    #[unstable(feature = "char_error_internals",
+               reason = "this method should not be available publicly",
+               issue = "0")]
+    #[doc(hidden)]
+    pub fn __description(&self) -> &str {
+        match self.kind {
+            CharErrorKind::EmptyString => {
+                "cannot parse char from empty string"
+            },
+            CharErrorKind::TooManyChars => "too many characters in string"
+        }
+    }
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+enum CharErrorKind {
+    EmptyString,
+    TooManyChars,
+}
+
+#[stable(feature = "char_from_str", since = "1.20.0")]
+impl fmt::Display for ParseCharError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.__description().fmt(f)
+    }
+}
+
+
+#[stable(feature = "char_from_str", since = "1.20.0")]
+impl FromStr for char {
+    type Err = ParseCharError;
+
+    #[inline]
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let mut chars = s.chars();
+        match (chars.next(), chars.next()) {
+            (None, _) => {
+                Err(ParseCharError { kind: CharErrorKind::EmptyString })
+            },
+            (Some(c), None) => Ok(c),
+            _ => {
+                Err(ParseCharError { kind: CharErrorKind::TooManyChars })
+            }
+        }
+    }
+}
+
+
+#[stable(feature = "try_from", since = "1.26.0")]
+impl TryFrom<u32> for char {
+    type Error = CharTryFromError;
+
+    #[inline]
+    fn try_from(i: u32) -> Result<Self, Self::Error> {
+        if (i > MAX as u32) || (i >= 0xD800 && i <= 0xDFFF) {
+            Err(CharTryFromError(()))
+        } else {
+            Ok(unsafe { from_u32_unchecked(i) })
+        }
+    }
+}
+
+/// The error type returned when a conversion from u32 to char fails.
+#[stable(feature = "try_from", since = "1.26.0")]
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub struct CharTryFromError(());
+
+#[stable(feature = "try_from", since = "1.26.0")]
+impl fmt::Display for CharTryFromError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        "converted integer out of range for `char`".fmt(f)
+    }
+}
+
+/// 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:
+///
+/// ```
+/// use std::char;
+///
+/// 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:
+///
+/// ```
+/// use std::char;
+///
+/// let c = char::from_digit(20, 10);
+///
+/// assert_eq!(None, c);
+/// ```
+///
+/// Passing a large radix, causing a panic:
+///
+/// ```
+/// use std::thread;
+/// use std::char;
+///
+/// let result = thread::spawn(|| {
+///     // this panics
+///     let c = char::from_digit(1, 37);
+/// }).join();
+///
+/// assert!(result.is_err());
+/// ```
+#[inline]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn from_digit(num: u32, radix: u32) -> Option<char> {
+    if radix > 36 {
+        panic!("from_digit: radix is too high (maximum 36)");
+    }
+    if num < radix {
+        let num = num as u8;
+        if num < 10 {
+            Some((b'0' + num) as char)
+        } else {
+            Some((b'a' + num - 10) as char)
+        }
+    } else {
+        None
+    }
+}
+