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    // Copyright 2014-2015 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.

    use std::borrow::Cow;
    use std::collections::HashMap;
    use std::fmt;
    use std::ops::Index;
    use std::str::FromStr;
    use std::sync::Arc;

    use memchr::memchr;

    use exec::{Exec, ExecNoSync};
    use expand::expand_bytes;
    use error::Error;
    use re_builder::bytes::RegexBuilder;
    use re_trait::{self, RegularExpression, SubCapturesPosIter};

    /// Match represents a single match of a regex in a haystack.
    ///
    /// The lifetime parameter `'t` refers to the lifetime of the matched text.
    #[derive(Copy, Clone, Debug, Eq, PartialEq)]
    pub struct Match<'t> {
        text: &'t [u8],
        start: usize,
        end: usize,
    }

    impl<'t> Match<'t> {
        /// Returns the starting byte offset of the match in the haystack.
        #[inline]
        pub fn start(&self) -> usize {
            self.start
        }

        /// Returns the ending byte offset of the match in the haystack.
        #[inline]
        pub fn end(&self) -> usize {
            self.end
        }

        /// Returns the matched text.
        #[inline]
        pub fn as_bytes(&self) -> &'t [u8] {
            &self.text[self.start..self.end]
        }

        /// Creates a new match from the given haystack and byte offsets.
        #[inline]
        fn new(haystack: &'t [u8], start: usize, end: usize) -> Match<'t> {
            Match {
                text: haystack,
                start: start,
                end: end,
            }
        }
    }

    /// A compiled regular expression for matching arbitrary bytes.
    ///
    /// It can be used to search, split or replace text. All searching is done with
    /// an implicit `.*?` at the beginning and end of an expression. To force an
    /// expression to match the whole string (or a prefix or a suffix), you must
    /// use an anchor like `^` or `$` (or `\A` and `\z`).
    ///
    /// Like the `Regex` type in the parent module, matches with this regex return
    /// byte offsets into the search text. **Unlike** the parent `Regex` type,
    /// these byte offsets may not correspond to UTF-8 sequence boundaries since
    /// the regexes in this module can match arbitrary bytes.
    #[derive(Clone)]
    pub struct Regex(Exec);

    impl fmt::Display for Regex {
        /// Shows the original regular expression.
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            write!(f, "{}", self.as_str())
        }
    }

    impl fmt::Debug for Regex {
        /// Shows the original regular expression.
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            fmt::Display::fmt(self, f)
        }
    }

    /// A constructor for Regex from an Exec.
    ///
    /// This is hidden because Exec isn't actually part of the public API.
    #[doc(hidden)]
    impl From<Exec> for Regex {
        fn from(exec: Exec) -> Regex {
            Regex(exec)
        }
    }

    impl FromStr for Regex {
        type Err = Error;

        /// Attempts to parse a string into a regular expression
        fn from_str(s: &str) -> Result<Regex, Error> {
            Regex::new(s)
        }
    }

    /// Core regular expression methods.
    impl Regex {
        /// Compiles a regular expression. Once compiled, it can be used repeatedly
        /// to search, split or replace text in a string.
        ///
        /// If an invalid expression is given, then an error is returned.
        pub fn new(re: &str) -> Result<Regex, Error> {
            RegexBuilder::new(re).build()
        }

        /// Returns true if and only if the regex matches the string given.
        ///
        /// It is recommended to use this method if all you need to do is test
        /// a match, since the underlying matching engine may be able to do less
        /// work.
        ///
        /// # Example
        ///
        /// Test if some text contains at least one word with exactly 13 ASCII word
        /// bytes:
        ///
        /// ```rust
        /// # extern crate regex; use regex::bytes::Regex;
        /// # fn main() {
        /// let text = b"I categorically deny having triskaidekaphobia.";
        /// assert!(Regex::new(r"\b\w{13}\b").unwrap().is_match(text));
        /// # }
        /// ```
        pub fn is_match(&self, text: &[u8]) -> bool {
            self.is_match_at(text, 0)
        }

        /// Returns the start and end byte range of the leftmost-first match in
        /// `text`. If no match exists, then `None` is returned.
        ///
        /// Note that this should only be used if you want to discover the position
        /// of the match. Testing the existence of a match is faster if you use
        /// `is_match`.
        ///
        /// # Example
        ///
        /// Find the start and end location of the first word with exactly 13
        /// ASCII word bytes:
        ///
        /// ```rust
        /// # extern crate regex; use regex::bytes::Regex;
        /// # fn main() {
        /// let text = b"I categorically deny having triskaidekaphobia.";
        /// let mat = Regex::new(r"\b\w{13}\b").unwrap().find(text).unwrap();
        /// assert_eq!((mat.start(), mat.end()), (2, 15));
        /// # }
        /// ```
        pub fn find<'t>(&self, text: &'t [u8]) -> Option<Match<'t>> {
            self.find_at(text, 0)
        }

        /// Returns an iterator for each successive non-overlapping match in
        /// `text`, returning the start and end byte indices with respect to
        /// `text`.
        ///
        /// # Example
        ///
        /// Find the start and end location of every word with exactly 13 ASCII
        /// word bytes:
        ///
        /// ```rust
        /// # extern crate regex; use regex::bytes::Regex;
        /// # fn main() {
        /// let text = b"Retroactively relinquishing remunerations is reprehensible.";
        /// for mat in Regex::new(r"\b\w{13}\b").unwrap().find_iter(text) {
        ///     println!("{:?}", mat);
        /// }
        /// # }
        /// ```
        pub fn find_iter<'r, 't>(&'r self, text: &'t [u8]) -> Matches<'r, 't> {
            Matches(self.0.searcher().find_iter(text))
        }

        /// Returns the capture groups corresponding to the leftmost-first
        /// match in `text`. Capture group `0` always corresponds to the entire
        /// match. If no match is found, then `None` is returned.
        ///
        /// You should only use `captures` if you need access to the location of
        /// capturing group matches. Otherwise, `find` is faster for discovering
        /// the location of the overall match.
        ///
        /// # Examples
        ///
        /// Say you have some text with movie names and their release years,
        /// like "'Citizen Kane' (1941)". It'd be nice if we could search for text
        /// looking like that, while also extracting the movie name and its release
        /// year separately.
        ///
        /// ```rust
        /// # extern crate regex; use regex::bytes::Regex;
        /// # fn main() {
        /// let re = Regex::new(r"'([^']+)'\s+\((\d{4})\)").unwrap();
        /// let text = b"Not my favorite movie: 'Citizen Kane' (1941).";
        /// let caps = re.captures(text).unwrap();
        /// assert_eq!(caps.get(1).unwrap().as_bytes(), &b"Citizen Kane"[..]);
        /// assert_eq!(caps.get(2).unwrap().as_bytes(), &b"1941"[..]);
        /// assert_eq!(caps.get(0).unwrap().as_bytes(), &b"'Citizen Kane' (1941)"[..]);
        /// // You can also access the groups by index using the Index notation.
        /// // Note that this will panic on an invalid index.
        /// assert_eq!(&caps[1], b"Citizen Kane");
        /// assert_eq!(&caps[2], b"1941");
        /// assert_eq!(&caps[0], b"'Citizen Kane' (1941)");
        /// # }
        /// ```
        ///
        /// Note that the full match is at capture group `0`. Each subsequent
        /// capture group is indexed by the order of its opening `(`.
        ///
        /// We can make this example a bit clearer by using *named* capture groups:
        ///
        /// ```rust
        /// # extern crate regex; use regex::bytes::Regex;
        /// # fn main() {
        /// let re = Regex::new(r"'(?P<title>[^']+)'\s+\((?P<year>\d{4})\)")
        ///                .unwrap();
        /// let text = b"Not my favorite movie: 'Citizen Kane' (1941).";
        /// let caps = re.captures(text).unwrap();
        /// assert_eq!(caps.name("title").unwrap().as_bytes(), b"Citizen Kane");
        /// assert_eq!(caps.name("year").unwrap().as_bytes(), b"1941");
        /// assert_eq!(caps.get(0).unwrap().as_bytes(), &b"'Citizen Kane' (1941)"[..]);
        /// // You can also access the groups by name using the Index notation.
        /// // Note that this will panic on an invalid group name.
        /// assert_eq!(&caps["title"], b"Citizen Kane");
        /// assert_eq!(&caps["year"], b"1941");
        /// assert_eq!(&caps[0], b"'Citizen Kane' (1941)");
        ///
        /// # }
        /// ```
        ///
        /// Here we name the capture groups, which we can access with the `name`
        /// method or the `Index` notation with a `&str`. Note that the named
        /// capture groups are still accessible with `get` or the `Index` notation
        /// with a `usize`.
        ///
        /// The `0`th capture group is always unnamed, so it must always be
        /// accessed with `get(0)` or `[0]`.
        pub fn captures<'t>(&self, text: &'t [u8]) -> Option<Captures<'t>> {
            let mut locs = self.capture_locations();
            self.captures_read_at(&mut locs, text, 0).map(move |_| Captures {
                text: text,
                locs: locs.0,
                named_groups: self.0.capture_name_idx().clone(),
            })
        }

        /// Returns an iterator over all the non-overlapping capture groups matched
        /// in `text`. This is operationally the same as `find_iter`, except it
        /// yields information about capturing group matches.
        ///
        /// # Example
        ///
        /// We can use this to find all movie titles and their release years in
        /// some text, where the movie is formatted like "'Title' (xxxx)":
        ///
        /// ```rust
        /// # extern crate regex; use std::str; use regex::bytes::Regex;
        /// # fn main() {
        /// let re = Regex::new(r"'(?P<title>[^']+)'\s+\((?P<year>\d{4})\)")
        ///                .unwrap();
        /// let text = b"'Citizen Kane' (1941), 'The Wizard of Oz' (1939), 'M' (1931).";
        /// for caps in re.captures_iter(text) {
        ///     let title = str::from_utf8(&caps["title"]).unwrap();
        ///     let year = str::from_utf8(&caps["year"]).unwrap();
        ///     println!("Movie: {:?}, Released: {:?}", title, year);
        /// }
        /// // Output:
        /// // Movie: Citizen Kane, Released: 1941
        /// // Movie: The Wizard of Oz, Released: 1939
        /// // Movie: M, Released: 1931
        /// # }
        /// ```
        pub fn captures_iter<'r, 't>(
            &'r self,
            text: &'t [u8],
        ) -> CaptureMatches<'r, 't> {
            CaptureMatches(self.0.searcher().captures_iter(text))
        }

        /// Returns an iterator of substrings of `text` delimited by a match of the
        /// regular expression. Namely, each element of the iterator corresponds to
        /// text that *isn't* matched by the regular expression.
        ///
        /// This method will *not* copy the text given.
        ///
        /// # Example
        ///
        /// To split a string delimited by arbitrary amounts of spaces or tabs:
        ///
        /// ```rust
        /// # extern crate regex; use regex::bytes::Regex;
        /// # fn main() {
        /// let re = Regex::new(r"[ \t]+").unwrap();
        /// let fields: Vec<&[u8]> = re.split(b"a b \t  c\td    e").collect();
        /// assert_eq!(fields, vec![
        ///     &b"a"[..], &b"b"[..], &b"c"[..], &b"d"[..], &b"e"[..],
        /// ]);
        /// # }
        /// ```
        pub fn split<'r, 't>(&'r self, text: &'t [u8]) -> Split<'r, 't> {
            Split {
                finder: self.find_iter(text),
                last: 0,
            }
        }

        /// Returns an iterator of at most `limit` substrings of `text` delimited
        /// by a match of the regular expression. (A `limit` of `0` will return no
        /// substrings.) Namely, each element of the iterator corresponds to text
        /// that *isn't* matched by the regular expression. The remainder of the
        /// string that is not split will be the last element in the iterator.
        ///
        /// This method will *not* copy the text given.
        ///
        /// # Example
        ///
        /// Get the first two words in some text:
        ///
        /// ```rust
        /// # extern crate regex; use regex::bytes::Regex;
        /// # fn main() {
        /// let re = Regex::new(r"\W+").unwrap();
        /// let fields: Vec<&[u8]> = re.splitn(b"Hey! How are you?", 3).collect();
        /// assert_eq!(fields, vec![&b"Hey"[..], &b"How"[..], &b"are you?"[..]]);
        /// # }
        /// ```
        pub fn splitn<'r, 't>(
            &'r self,
            text: &'t [u8],
            limit: usize,
        ) -> SplitN<'r, 't> {
            SplitN {
                splits: self.split(text),
                n: limit,
            }
        }

        /// Replaces the leftmost-first match with the replacement provided. The
        /// replacement can be a regular byte string (where `$N` and `$name` are
        /// expanded to match capture groups) or a function that takes the matches'
        /// `Captures` and returns the replaced byte string.
        ///
        /// If no match is found, then a copy of the byte string is returned
        /// unchanged.
        ///
        /// # Replacement string syntax
        ///
        /// All instances of `$name` in the replacement text is replaced with the
        /// corresponding capture group `name`.
        ///
        /// `name` may be an integer corresponding to the index of the
        /// capture group (counted by order of opening parenthesis where `0` is the
        /// entire match) or it can be a name (consisting of letters, digits or
        /// underscores) corresponding to a named capture group.
        ///
        /// If `name` isn't a valid capture group (whether the name doesn't exist
        /// or isn't a valid index), then it is replaced with the empty string.
        ///
        /// The longest possible name is used. e.g., `$1a` looks up the capture
        /// group named `1a` and not the capture group at index `1`. To exert more
        /// precise control over the name, use braces, e.g., `${1}a`.
        ///
        /// To write a literal `$` use `$$`.
        ///
        /// # Examples
        ///
        /// Note that this function is polymorphic with respect to the replacement.
        /// In typical usage, this can just be a normal byte string:
        ///
        /// ```rust
        /// # extern crate regex; use regex::bytes::Regex;
        /// # fn main() {
        /// let re = Regex::new("[^01]+").unwrap();
        /// assert_eq!(re.replace(b"1078910", &b""[..]), &b"1010"[..]);
        /// # }
        /// ```
        ///
        /// But anything satisfying the `Replacer` trait will work. For example, a
        /// closure of type `|&Captures| -> Vec<u8>` provides direct access to the
        /// captures corresponding to a match. This allows one to access capturing
        /// group matches easily:
        ///
        /// ```rust
        /// # extern crate regex; use regex::bytes::Regex;
        /// # use regex::bytes::Captures; fn main() {
        /// let re = Regex::new(r"([^,\s]+),\s+(\S+)").unwrap();
        /// let result = re.replace(b"Springsteen, Bruce", |caps: &Captures| {
        ///     let mut replacement = caps[2].to_owned();
        ///     replacement.push(b' ');
        ///     replacement.extend(&caps[1]);
        ///     replacement
        /// });
        /// assert_eq!(result, &b"Bruce Springsteen"[..]);
        /// # }
        /// ```
        ///
        /// But this is a bit cumbersome to use all the time. Instead, a simple
        /// syntax is supported that expands `$name` into the corresponding capture
        /// group. Here's the last example, but using this expansion technique
        /// with named capture groups:
        ///
        /// ```rust
        /// # extern crate regex; use regex::bytes::Regex;
        /// # fn main() {
        /// let re = Regex::new(r"(?P<last>[^,\s]+),\s+(?P<first>\S+)").unwrap();
        /// let result = re.replace(b"Springsteen, Bruce", &b"$first $last"[..]);
        /// assert_eq!(result, &b"Bruce Springsteen"[..]);
        /// # }
        /// ```
        ///
        /// Note that using `$2` instead of `$first` or `$1` instead of `$last`
        /// would produce the same result. To write a literal `$` use `$$`.
        ///
        /// Sometimes the replacement string requires use of curly braces to
        /// delineate a capture group replacement and surrounding literal text.
        /// For example, if we wanted to join two words together with an
        /// underscore:
        ///
        /// ```rust
        /// # extern crate regex; use regex::bytes::Regex;
        /// # fn main() {
        /// let re = Regex::new(r"(?P<first>\w+)\s+(?P<second>\w+)").unwrap();
        /// let result = re.replace(b"deep fried", &b"${first}_$second"[..]);
        /// assert_eq!(result, &b"deep_fried"[..]);
        /// # }
        /// ```
        ///
        /// Without the curly braces, the capture group name `first_` would be
        /// used, and since it doesn't exist, it would be replaced with the empty
        /// string.
        ///
        /// Finally, sometimes you just want to replace a literal string with no
        /// regard for capturing group expansion. This can be done by wrapping a
        /// byte string with `NoExpand`:
        ///
        /// ```rust
        /// # extern crate regex; use regex::bytes::Regex;
        /// # fn main() {
        /// use regex::bytes::NoExpand;
        ///
        /// let re = Regex::new(r"(?P<last>[^,\s]+),\s+(\S+)").unwrap();
        /// let result = re.replace(b"Springsteen, Bruce", NoExpand(b"$2 $last"));
        /// assert_eq!(result, &b"$2 $last"[..]);
        /// # }
        /// ```
        pub fn replace<'t, R: Replacer>(
            &self,
            text: &'t [u8],
            rep: R,
        ) -> Cow<'t, [u8]> {
            self.replacen(text, 1, rep)
        }

        /// Replaces all non-overlapping matches in `text` with the replacement
        /// provided. This is the same as calling `replacen` with `limit` set to
        /// `0`.
        ///
        /// See the documentation for `replace` for details on how to access
        /// capturing group matches in the replacement text.
        pub fn replace_all<'t, R: Replacer>(
            &self,
            text: &'t [u8],
            rep: R,
        ) -> Cow<'t, [u8]> {
            self.replacen(text, 0, rep)
        }

        /// Replaces at most `limit` non-overlapping matches in `text` with the
        /// replacement provided. If `limit` is 0, then all non-overlapping matches
        /// are replaced.
        ///
        /// See the documentation for `replace` for details on how to access
        /// capturing group matches in the replacement text.
        pub fn replacen<'t, R: Replacer>(
            &self,
            text: &'t [u8],
            limit: usize,
            mut rep: R,
        ) -> Cow<'t, [u8]> {
            if let Some(rep) = rep.no_expansion() {
                let mut it = self.find_iter(text).enumerate().peekable();
                if it.peek().is_none() {
                    return Cow::Borrowed(text);
                }
                let mut new = Vec::with_capacity(text.len());
                let mut last_match = 0;
                for (i, m) in it {
                    if limit > 0 && i >= limit {
                        break
                    }
                    new.extend_from_slice(&text[last_match..m.start()]);
                    new.extend_from_slice(&rep);
                    last_match = m.end();
                }
                new.extend_from_slice(&text[last_match..]);
                return Cow::Owned(new);
            }

            // The slower path, which we use if the replacement needs access to
            // capture groups.
            let mut it = self.captures_iter(text).enumerate().peekable();
            if it.peek().is_none() {
                return Cow::Borrowed(text);
            }
            let mut new = Vec::with_capacity(text.len());
            let mut last_match = 0;
            for (i, cap) in it {
                if limit > 0 && i >= limit {
                    break
                }
                // unwrap on 0 is OK because captures only reports matches
                let m = cap.get(0).unwrap();
                new.extend_from_slice(&text[last_match..m.start()]);
                rep.replace_append(&cap, &mut new);
                last_match = m.end();
            }
            new.extend_from_slice(&text[last_match..]);
            Cow::Owned(new)
        }
    }

    /// Advanced or "lower level" search methods.
    impl Regex {
        /// Returns the end location of a match in the text given.
        ///
        /// This method may have the same performance characteristics as
        /// `is_match`, except it provides an end location for a match. In
        /// particular, the location returned *may be shorter* than the proper end
        /// of the leftmost-first match.
        ///
        /// # Example
        ///
        /// Typically, `a+` would match the entire first sequence of `a` in some
        /// text, but `shortest_match` can give up as soon as it sees the first
        /// `a`.
        ///
        /// ```rust
        /// # extern crate regex; use regex::bytes::Regex;
        /// # fn main() {
        /// let text = b"aaaaa";
        /// let pos = Regex::new(r"a+").unwrap().shortest_match(text);
        /// assert_eq!(pos, Some(1));
        /// # }
        /// ```
        pub fn shortest_match(&self, text: &[u8]) -> Option<usize> {
            self.shortest_match_at(text, 0)
        }

        /// Returns the same as shortest_match, but starts the search at the given
        /// offset.
        ///
        /// The significance of the starting point is that it takes the surrounding
        /// context into consideration. For example, the `\A` anchor can only
        /// match when `start == 0`.
        pub fn shortest_match_at(
            &self,
            text: &[u8],
            start: usize,
        ) -> Option<usize> {
            self.0.searcher().shortest_match_at(text, start)
        }

        /// Returns the same as is_match, but starts the search at the given
        /// offset.
        ///
        /// The significance of the starting point is that it takes the surrounding
        /// context into consideration. For example, the `\A` anchor can only
        /// match when `start == 0`.
        pub fn is_match_at(&self, text: &[u8], start: usize) -> bool {
            self.shortest_match_at(text, start).is_some()
        }

        /// Returns the same as find, but starts the search at the given
        /// offset.
        ///
        /// The significance of the starting point is that it takes the surrounding
        /// context into consideration. For example, the `\A` anchor can only
        /// match when `start == 0`.
        pub fn find_at<'t>(
            &self,
            text: &'t [u8],
            start: usize,
        ) -> Option<Match<'t>> {
            self.0.searcher().find_at(text, start)
                .map(|(s, e)| Match::new(text, s, e))
        }

        /// This is like `captures`, but uses
        /// [`CaptureLocations`](struct.CaptureLocations.html)
        /// instead of
        /// [`Captures`](struct.Captures.html) in order to amortize allocations.
        ///
        /// To create a `CaptureLocations` value, use the
        /// `Regex::capture_locations` method.
        ///
        /// This returns the overall match if this was successful, which is always
        /// equivalence to the `0`th capture group.
        pub fn captures_read<'t>(
            &self,
            locs: &mut CaptureLocations,
            text: &'t [u8],
        ) -> Option<Match<'t>> {
            self.captures_read_at(locs, text, 0)
        }

        /// Returns the same as `captures_read`, but starts the search at the given
        /// offset and populates the capture locations given.
        ///
        /// The significance of the starting point is that it takes the surrounding
        /// context into consideration. For example, the `\A` anchor can only
        /// match when `start == 0`.
        pub fn captures_read_at<'t>(
            &self,
            locs: &mut CaptureLocations,
            text: &'t [u8],
            start: usize,
        ) -> Option<Match<'t>> {
            self.0
                .searcher()
                .captures_read_at(&mut locs.0, text, start)
                .map(|(s, e)| Match::new(text, s, e))
        }

        /// An undocumented alias for `captures_read_at`.
        ///
        /// The `regex-capi` crate previously used this routine, so to avoid
        /// breaking that crate, we continue to provide the name as an undocumented
        /// alias.
        #[doc(hidden)]
        pub fn read_captures_at<'t>(
            &self,
            locs: &mut CaptureLocations,
            text: &'t [u8],
            start: usize,
        ) -> Option<Match<'t>> {
            self.captures_read_at(locs, text, start)
        }
    }

    /// Auxiliary methods.
    impl Regex {
        /// Returns the original string of this regex.
        pub fn as_str(&self) -> &str {
            &self.0.regex_strings()[0]
        }

        /// Returns an iterator over the capture names.
        pub fn capture_names(&self) -> CaptureNames {
            CaptureNames(self.0.capture_names().iter())
        }

        /// Returns the number of captures.
        pub fn captures_len(&self) -> usize {
            self.0.capture_names().len()
        }

        /// Returns an empty set of capture locations that can be reused in
        /// multiple calls to `captures_read` or `captures_read_at`.
        pub fn capture_locations(&self) -> CaptureLocations {
            CaptureLocations(self.0.searcher().locations())
        }

        /// An alias for `capture_locations` to preserve backward compatibility.
        ///
        /// The `regex-capi` crate uses this method, so to avoid breaking that
        /// crate, we continue to export it as an undocumented API.
        #[doc(hidden)]
        pub fn locations(&self) -> CaptureLocations {
            CaptureLocations(self.0.searcher().locations())
        }
    }

    /// An iterator over all non-overlapping matches for a particular string.
    ///
    /// The iterator yields a tuple of integers corresponding to the start and end
    /// of the match. The indices are byte offsets. The iterator stops when no more
    /// matches can be found.
    ///
    /// `'r` is the lifetime of the compiled regular expression and `'t` is the
    /// lifetime of the matched byte string.
    pub struct Matches<'r, 't>(re_trait::Matches<'t, ExecNoSync<'r>>);

    impl<'r, 't> Iterator for Matches<'r, 't> {
        type Item = Match<'t>;

        fn next(&mut self) -> Option<Match<'t>> {
            let text = self.0.text();
            self.0.next().map(|(s, e)| Match::new(text, s, e))
        }
    }

    /// An iterator that yields all non-overlapping capture groups matching a
    /// particular regular expression.
    ///
    /// The iterator stops when no more matches can be found.
    ///
    /// `'r` is the lifetime of the compiled regular expression and `'t` is the
    /// lifetime of the matched byte string.
    pub struct CaptureMatches<'r, 't>(re_trait::CaptureMatches<'t, ExecNoSync<'r>>);

    impl<'r, 't> Iterator for CaptureMatches<'r, 't> {
        type Item = Captures<'t>;

        fn next(&mut self) -> Option<Captures<'t>> {
            self.0.next().map(|locs| Captures {
                text: self.0.text(),
                locs: locs,
                named_groups: self.0.regex().capture_name_idx().clone(),
            })
        }
    }

    /// Yields all substrings delimited by a regular expression match.
    ///
    /// `'r` is the lifetime of the compiled regular expression and `'t` is the
    /// lifetime of the byte string being split.
    pub struct Split<'r, 't> {
        finder: Matches<'r, 't>,
        last: usize,
    }

    impl<'r, 't> Iterator for Split<'r, 't> {
        type Item = &'t [u8];

        fn next(&mut self) -> Option<&'t [u8]> {
            let text = self.finder.0.text();
            match self.finder.next() {
                None => {
                    if self.last >= text.len() {
                        None
                    } else {
                        let s = &text[self.last..];
                        self.last = text.len();
                        Some(s)
                    }
                }
                Some(m) => {
                    let matched = &text[self.last..m.start()];
                    self.last = m.end();
                    Some(matched)
                }
            }
        }
    }

    /// Yields at most `N` substrings delimited by a regular expression match.
    ///
    /// The last substring will be whatever remains after splitting.
    ///
    /// `'r` is the lifetime of the compiled regular expression and `'t` is the
    /// lifetime of the byte string being split.
    pub struct SplitN<'r, 't> {
        splits: Split<'r, 't>,
        n: usize,
    }

    impl<'r, 't> Iterator for SplitN<'r, 't> {
        type Item = &'t [u8];

        fn next(&mut self) -> Option<&'t [u8]> {
            if self.n == 0 {
                return None
            }
            self.n -= 1;
            if self.n == 0 {
                let text = self.splits.finder.0.text();
                Some(&text[self.splits.last..])
            } else {
                self.splits.next()
            }
        }
    }

    /// An iterator over the names of all possible captures.
    ///
    /// `None` indicates an unnamed capture; the first element (capture 0, the
    /// whole matched region) is always unnamed.
    ///
    /// `'r` is the lifetime of the compiled regular expression.
    pub struct CaptureNames<'r>(::std::slice::Iter<'r, Option<String>>);

    impl<'r> Iterator for CaptureNames<'r> {
        type Item = Option<&'r str>;

        fn next(&mut self) -> Option<Option<&'r str>> {
            self.0.next().as_ref()
                .map(|slot| slot.as_ref().map(|name| name.as_ref()))
        }

        fn size_hint(&self) -> (usize, Option<usize>) {
            self.0.size_hint()
        }
    }

    /// CaptureLocations is a low level representation of the raw offsets of each
    /// submatch.
    ///
    /// You can think of this as a lower level
    /// [`Captures`](struct.Captures.html), where this type does not support
    /// named capturing groups directly and it does not borrow the text that these
    /// offsets were matched on.
    ///
    /// Primarily, this type is useful when using the lower level `Regex` APIs
    /// such as `read_captures`, which permits amortizing the allocation in which
    /// capture match locations are stored.
    ///
    /// In order to build a value of this type, you'll need to call the
    /// `capture_locations` method on the `Regex` being used to execute the search.
    /// The value returned can then be reused in subsequent searches.
    #[derive(Clone, Debug)]
    pub struct CaptureLocations(re_trait::Locations);

    /// A type alias for `CaptureLocations` for backwards compatibility.
    ///
    /// Previously, we exported `CaptureLocations` as `Locations` in an
    /// undocumented API. To prevent breaking that code (e.g., in `regex-capi`),
    /// we continue re-exporting the same undocumented API.
    #[doc(hidden)]
    pub type Locations = CaptureLocations;

    impl CaptureLocations {
        /// Returns the start and end positions of the Nth capture group. Returns
        /// `None` if `i` is not a valid capture group or if the capture group did
        /// not match anything. The positions returned are *always* byte indices
        /// with respect to the original string matched.
        #[inline]
        pub fn get(&self, i: usize) -> Option<(usize, usize)> {
            self.0.pos(i)
        }

        /// Returns the total number of capturing groups.
        ///
        /// This is always at least `1` since every regex has at least `1`
        /// capturing group that corresponds to the entire match.
        #[inline]
        pub fn len(&self) -> usize {
            self.0.len()
        }

        /// An alias for the `get` method for backwards compatibility.
        ///
        /// Previously, we exported `get` as `pos` in an undocumented API. To
        /// prevent breaking that code (e.g., in `regex-capi`), we continue
        /// re-exporting the same undocumented API.
        #[doc(hidden)]
        #[inline]
        pub fn pos(&self, i: usize) -> Option<(usize, usize)> {
            self.get(i)
        }
    }

    /// Captures represents a group of captured byte strings for a single match.
    ///
    /// The 0th capture always corresponds to the entire match. Each subsequent
    /// index corresponds to the next capture group in the regex. If a capture
    /// group is named, then the matched byte string is *also* available via the
    /// `name` method. (Note that the 0th capture is always unnamed and so must be
    /// accessed with the `get` method.)
    ///
    /// Positions returned from a capture group are always byte indices.
    ///
    /// `'t` is the lifetime of the matched text.
    pub struct Captures<'t> {
        text: &'t [u8],
        locs: re_trait::Locations,
        named_groups: Arc<HashMap<String, usize>>,
    }

    impl<'t> Captures<'t> {
        /// Returns the match associated with the capture group at index `i`. If
        /// `i` does not correspond to a capture group, or if the capture group
        /// did not participate in the match, then `None` is returned.
        ///
        /// # Examples
        ///
        /// Get the text of the match with a default of an empty string if this
        /// group didn't participate in the match:
        ///
        /// ```rust
        /// # use regex::bytes::Regex;
        /// let re = Regex::new(r"[a-z]+(?:([0-9]+)|([A-Z]+))").unwrap();
        /// let caps = re.captures(b"abc123").unwrap();
        ///
        /// let text1 = caps.get(1).map_or(&b""[..], |m| m.as_bytes());
        /// let text2 = caps.get(2).map_or(&b""[..], |m| m.as_bytes());
        /// assert_eq!(text1, &b"123"[..]);
        /// assert_eq!(text2, &b""[..]);
        /// ```
        pub fn get(&self, i: usize) -> Option<Match<'t>> {
            self.locs.pos(i).map(|(s, e)| Match::new(self.text, s, e))
        }

        /// Returns the match for the capture group named `name`. If `name` isn't a
        /// valid capture group or didn't match anything, then `None` is returned.
        pub fn name(&self, name: &str) -> Option<Match<'t>> {
            self.named_groups.get(name).and_then(|&i| self.get(i))
        }

        /// An iterator that yields all capturing matches in the order in which
        /// they appear in the regex. If a particular capture group didn't
        /// participate in the match, then `None` is yielded for that capture.
        ///
        /// The first match always corresponds to the overall match of the regex.
        pub fn iter<'c>(&'c self) -> SubCaptureMatches<'c, 't> {
            SubCaptureMatches {
                caps: self,
                it: self.locs.iter(),
            }
        }

        /// Expands all instances of `$name` in `replacement` to the corresponding
        /// capture group `name`, and writes them to the `dst` buffer given.
        ///
        /// `name` may be an integer corresponding to the index of the
        /// capture group (counted by order of opening parenthesis where `0` is the
        /// entire match) or it can be a name (consisting of letters, digits or
        /// underscores) corresponding to a named capture group.
        ///
        /// If `name` isn't a valid capture group (whether the name doesn't exist
        /// or isn't a valid index), then it is replaced with the empty string.
        ///
        /// The longest possible name is used. e.g., `$1a` looks up the capture
        /// group named `1a` and not the capture group at index `1`. To exert more
        /// precise control over the name, use braces, e.g., `${1}a`.
        ///
        /// To write a literal `$` use `$$`.
        pub fn expand(&self, replacement: &[u8], dst: &mut Vec<u8>) {
            expand_bytes(self, replacement, dst)
        }

        /// Returns the number of captured groups.
        ///
        /// This is always at least `1`, since every regex has at least one capture
        /// group that corresponds to the full match.
        #[inline]
        pub fn len(&self) -> usize {
            self.locs.len()
        }
    }

    impl<'t> fmt::Debug for Captures<'t> {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            f.debug_tuple("Captures").field(&CapturesDebug(self)).finish()
        }
    }

    struct CapturesDebug<'c, 't: 'c>(&'c Captures<'t>);

    impl<'c, 't> fmt::Debug for CapturesDebug<'c, 't> {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            fn escape_bytes(bytes: &[u8]) -> String {
                let mut s = String::new();
                for &b in bytes {
                    s.push_str(&escape_byte(b));
                }
                s
            }

            fn escape_byte(byte: u8) -> String {
                use std::ascii::escape_default;

                let escaped: Vec<u8> = escape_default(byte).collect();
                String::from_utf8_lossy(&escaped).into_owned()
            }

            // We'd like to show something nice here, even if it means an
            // allocation to build a reverse index.
            let slot_to_name: HashMap<&usize, &String> =
                self.0.named_groups.iter().map(|(a, b)| (b, a)).collect();
            let mut map = f.debug_map();
            for (slot, m) in self.0.locs.iter().enumerate() {
                let m = m.map(|(s, e)| escape_bytes(&self.0.text[s..e]));
                if let Some(name) = slot_to_name.get(&slot) {
                    map.entry(&name, &m);
                } else {
                    map.entry(&slot, &m);
                }
            }
            map.finish()
        }
    }

    /// Get a group by index.
    ///
    /// `'t` is the lifetime of the matched text.
    ///
    /// The text can't outlive the `Captures` object if this method is
    /// used, because of how `Index` is defined (normally `a[i]` is part
    /// of `a` and can't outlive it); to do that, use `get()` instead.
    ///
    /// # Panics
    ///
    /// If there is no group at the given index.
    impl<'t> Index<usize> for Captures<'t> {
        type Output = [u8];

        fn index(&self, i: usize) -> &[u8] {
            self.get(i).map(|m| m.as_bytes())
                .unwrap_or_else(|| panic!("no group at index '{}'", i))
        }
    }

    /// Get a group by name.
    ///
    /// `'t` is the lifetime of the matched text and `'i` is the lifetime
    /// of the group name (the index).
    ///
    /// The text can't outlive the `Captures` object if this method is
    /// used, because of how `Index` is defined (normally `a[i]` is part
    /// of `a` and can't outlive it); to do that, use `name` instead.
    ///
    /// # Panics
    ///
    /// If there is no group named by the given value.
    impl<'t, 'i> Index<&'i str> for Captures<'t> {
        type Output = [u8];

        fn index<'a>(&'a self, name: &'i str) -> &'a [u8] {
            self.name(name).map(|m| m.as_bytes())
                .unwrap_or_else(|| panic!("no group named '{}'", name))
        }
    }

    /// An iterator that yields all capturing matches in the order in which they
    /// appear in the regex.
    ///
    /// If a particular capture group didn't participate in the match, then `None`
    /// is yielded for that capture. The first match always corresponds to the
    /// overall match of the regex.
    ///
    /// The lifetime `'c` corresponds to the lifetime of the `Captures` value, and
    /// the lifetime `'t` corresponds to the originally matched text.
    pub struct SubCaptureMatches<'c, 't: 'c> {
        caps: &'c Captures<'t>,
        it: SubCapturesPosIter<'c>,
    }

    impl<'c, 't> Iterator for SubCaptureMatches<'c, 't> {
        type Item = Option<Match<'t>>;

        fn next(&mut self) -> Option<Option<Match<'t>>> {
            self.it.next()
                .map(|cap| cap.map(|(s, e)| Match::new(self.caps.text, s, e)))
        }
    }

    /// Replacer describes types that can be used to replace matches in a byte
    /// string.
    ///
    /// In general, users of this crate shouldn't need to implement this trait,
    /// since implementations are already provided for `&[u8]` and
    /// `FnMut(&Captures) -> Vec<u8>` (or any `FnMut(&Captures) -> T`
    /// where `T: AsRef<[u8]>`), which covers most use cases.
    pub trait Replacer {
        /// Appends text to `dst` to replace the current match.
        ///
        /// The current match is represented by `caps`, which is guaranteed to
        /// have a match at capture group `0`.
        ///
        /// For example, a no-op replacement would be
        /// `dst.extend(&caps[0])`.
        fn replace_append(&mut self, caps: &Captures, dst: &mut Vec<u8>);

        /// Return a fixed unchanging replacement byte string.
        ///
        /// When doing replacements, if access to `Captures` is not needed (e.g.,
        /// the replacement byte string does not need `$` expansion), then it can
        /// be beneficial to avoid finding sub-captures.
        ///
        /// In general, this is called once for every call to `replacen`.
        fn no_expansion<'r>(&'r mut self) -> Option<Cow<'r, [u8]>> {
            None
        }

        /// Return a `Replacer` that borrows and wraps this `Replacer`.
        ///
        /// This is useful when you want to take a generic `Replacer` (which might
        /// not be cloneable) and use it without consuming it, so it can be used
        /// more than once.
        ///
        /// # Example
        ///
        /// ```
        /// use regex::bytes::{Regex, Replacer};
        ///
        /// fn replace_all_twice<R: Replacer>(
        ///     re: Regex,
        ///     src: &[u8],
        ///     mut rep: R,
        /// ) -> Vec<u8> {
        ///     let dst = re.replace_all(src, rep.by_ref());
        ///     let dst = re.replace_all(&dst, rep.by_ref());
        ///     dst.into_owned()
        /// }
        /// ```
        fn by_ref<'r>(&'r mut self) -> ReplacerRef<'r, Self> {
            ReplacerRef(self)
        }
    }

    /// By-reference adaptor for a `Replacer`
    ///
    /// Returned by [`Replacer::by_ref`](trait.Replacer.html#method.by_ref).
    #[derive(Debug)]
    pub struct ReplacerRef<'a, R: ?Sized + 'a>(&'a mut R);

    impl<'a, R: Replacer + ?Sized + 'a> Replacer for ReplacerRef<'a, R> {
        fn replace_append(&mut self, caps: &Captures, dst: &mut Vec<u8>) {
            self.0.replace_append(caps, dst)
        }
        fn no_expansion<'r>(&'r mut self) -> Option<Cow<'r, [u8]>> {
            self.0.no_expansion()
        }
    }

    impl<'a> Replacer for &'a [u8] {
        fn replace_append(&mut self, caps: &Captures, dst: &mut Vec<u8>) {
            caps.expand(*self, dst);
        }

        fn no_expansion(&mut self) -> Option<Cow<[u8]>> {
            match memchr(b'$', *self) {
                Some(_) => None,
                None => Some(Cow::Borrowed(*self)),
            }
        }
    }

    impl<F, T> Replacer for F where F: FnMut(&Captures) -> T, T: AsRef<[u8]> {
        fn replace_append(&mut self, caps: &Captures, dst: &mut Vec<u8>) {
            dst.extend_from_slice((*self)(caps).as_ref());
        }
    }

    /// `NoExpand` indicates literal byte string replacement.
    ///
    /// It can be used with `replace` and `replace_all` to do a literal byte string
    /// replacement without expanding `$name` to their corresponding capture
    /// groups. This can be both convenient (to avoid escaping `$`, for example)
    /// and performant (since capture groups don't need to be found).
    ///
    /// `'t` is the lifetime of the literal text.
    pub struct NoExpand<'t>(pub &'t [u8]);

    impl<'t> Replacer for NoExpand<'t> {
        fn replace_append(&mut self, _: &Captures, dst: &mut Vec<u8>) {
            dst.extend_from_slice(self.0);
        }

        fn no_expansion(&mut self) -> Option<Cow<[u8]>> {
            Some(Cow::Borrowed(self.0))
        }
    }

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