1 files changed, 151 insertions, 0 deletions
diff --git a/library/core/src/ascii.rs b/library/core/src/ascii.rs
new file mode 100644
index 000000000..8a4cb78cc
--- /dev/null
+++ b/library/core/src/ascii.rs
@@ -0,0 +1,151 @@
+//! Operations on ASCII strings and characters.
+//!
+//! Most string operations in Rust act on UTF-8 strings. However, at times it
+//! makes more sense to only consider the ASCII character set for a specific
+//! operation.
+//!
+//! The [`escape_default`] function provides an iterator over the bytes of an
+//! escaped version of the character given.
+
+#![stable(feature = "core_ascii", since = "1.26.0")]
+
+use crate::fmt;
+use crate::iter::FusedIterator;
+use crate::ops::Range;
+use crate::str::from_utf8_unchecked;
+
+/// An iterator over the escaped version of a byte.
+///
+/// This `struct` is created by the [`escape_default`] function. See its
+/// documentation for more.
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[derive(Clone)]
+pub struct EscapeDefault {
+    range: Range<u8>,
+    data: [u8; 4],
+}
+
+/// Returns an iterator that produces an escaped version of a `u8`.
+///
+/// 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.
+/// * Any other chars are given hex escapes of the form '\xNN'.
+/// * Unicode escapes are never generated by this function.
+///
+/// # Examples
+///
+/// ```
+/// use std::ascii;
+///
+/// let escaped = ascii::escape_default(b'0').next().unwrap();
+/// assert_eq!(b'0', escaped);
+///
+/// let mut escaped = ascii::escape_default(b'\t');
+///
+/// assert_eq!(b'\\', escaped.next().unwrap());
+/// assert_eq!(b't', escaped.next().unwrap());
+///
+/// let mut escaped = ascii::escape_default(b'\r');
+///
+/// assert_eq!(b'\\', escaped.next().unwrap());
+/// assert_eq!(b'r', escaped.next().unwrap());
+///
+/// let mut escaped = ascii::escape_default(b'\n');
+///
+/// assert_eq!(b'\\', escaped.next().unwrap());
+/// assert_eq!(b'n', escaped.next().unwrap());
+///
+/// let mut escaped = ascii::escape_default(b'\'');
+///
+/// assert_eq!(b'\\', escaped.next().unwrap());
+/// assert_eq!(b'\'', escaped.next().unwrap());
+///
+/// let mut escaped = ascii::escape_default(b'"');
+///
+/// assert_eq!(b'\\', escaped.next().unwrap());
+/// assert_eq!(b'"', escaped.next().unwrap());
+///
+/// let mut escaped = ascii::escape_default(b'\\');
+///
+/// assert_eq!(b'\\', escaped.next().unwrap());
+/// assert_eq!(b'\\', escaped.next().unwrap());
+///
+/// let mut escaped = ascii::escape_default(b'\x9d');
+///
+/// assert_eq!(b'\\', escaped.next().unwrap());
+/// assert_eq!(b'x', escaped.next().unwrap());
+/// assert_eq!(b'9', escaped.next().unwrap());
+/// assert_eq!(b'd', escaped.next().unwrap());
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn escape_default(c: u8) -> EscapeDefault {
+    let (data, len) = match c {
+        b'\t' => ([b'\\', b't', 0, 0], 2),
+        b'\r' => ([b'\\', b'r', 0, 0], 2),
+        b'\n' => ([b'\\', b'n', 0, 0], 2),
+        b'\\' => ([b'\\', b'\\', 0, 0], 2),
+        b'\'' => ([b'\\', b'\'', 0, 0], 2),
+        b'"' => ([b'\\', b'"', 0, 0], 2),
+        b'\x20'..=b'\x7e' => ([c, 0, 0, 0], 1),
+        _ => {
+            let hex_digits: &[u8; 16] = b"0123456789abcdef";
+            ([b'\\', b'x', hex_digits[(c >> 4) as usize], hex_digits[(c & 0xf) as usize]], 4)
+        }
+    };
+
+    return EscapeDefault { range: 0..len, data };
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Iterator for EscapeDefault {
+    type Item = u8;
+
+    #[inline]
+    fn next(&mut self) -> Option<u8> {
+        self.range.next().map(|i| self.data[i as usize])
+    }
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.range.size_hint()
+    }
+    fn last(mut self) -> Option<u8> {
+        self.next_back()
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl DoubleEndedIterator for EscapeDefault {
+    fn next_back(&mut self) -> Option<u8> {
+        self.range.next_back().map(|i| self.data[i as usize])
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl ExactSizeIterator for EscapeDefault {}
+#[stable(feature = "fused", since = "1.26.0")]
+impl FusedIterator for EscapeDefault {}
+
+#[stable(feature = "ascii_escape_display", since = "1.39.0")]
+impl fmt::Display for EscapeDefault {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        // SAFETY: ok because `escape_default` created only valid utf-8 data
+        f.write_str(unsafe {
+            from_utf8_unchecked(&self.data[(self.range.start as usize)..(self.range.end as usize)])
+        })
+    }
+}
+
+#[stable(feature = "std_debug", since = "1.16.0")]
+impl fmt::Debug for EscapeDefault {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("EscapeDefault").finish_non_exhaustive()
+    }
+}