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    // 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.

    //! Unicode-intensive string manipulations.
    //!
    //! This module provides functionality to `str` that requires the Unicode
    //! methods provided by the unicode parts of the CharExt trait.

    use core::char;
    use core::iter::Filter;
    use core::str::Split;

    /// An iterator over the non-whitespace substrings of a string,
    /// separated by any amount of whitespace.
    #[stable(feature = "split_whitespace", since = "1.1.0")]
    pub struct SplitWhitespace<'a> {
        inner: Filter<Split<'a, fn(char) -> bool>, fn(&&str) -> bool>,
    }

    /// Methods for Unicode string slices
    #[allow(missing_docs)] // docs in libcollections
    pub trait UnicodeStr {
        fn split_whitespace<'a>(&'a self) -> SplitWhitespace<'a>;
        fn is_whitespace(&self) -> bool;
        fn is_alphanumeric(&self) -> bool;
        fn trim(&self) -> &str;
        fn trim_left(&self) -> &str;
        fn trim_right(&self) -> &str;
    }

    impl UnicodeStr for str {
        #[inline]
        fn split_whitespace(&self) -> SplitWhitespace {
            fn is_not_empty(s: &&str) -> bool {
                !s.is_empty()
            }
            let is_not_empty: fn(&&str) -> bool = is_not_empty; // coerce to fn pointer

            fn is_whitespace(c: char) -> bool {
                c.is_whitespace()
            }
            let is_whitespace: fn(char) -> bool = is_whitespace; // coerce to fn pointer

            SplitWhitespace { inner: self.split(is_whitespace).filter(is_not_empty) }
        }

        #[inline]
        fn is_whitespace(&self) -> bool {
            self.chars().all(|c| c.is_whitespace())
        }

        #[inline]
        fn is_alphanumeric(&self) -> bool {
            self.chars().all(|c| c.is_alphanumeric())
        }

        #[inline]
        fn trim(&self) -> &str {
            self.trim_matches(|c: char| c.is_whitespace())
        }

        #[inline]
        fn trim_left(&self) -> &str {
            self.trim_left_matches(|c: char| c.is_whitespace())
        }

        #[inline]
        fn trim_right(&self) -> &str {
            self.trim_right_matches(|c: char| c.is_whitespace())
        }
    }

    // https://tools.ietf.org/html/rfc3629
    static UTF8_CHAR_WIDTH: [u8; 256] = [
    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 0x1F
    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 0x3F
    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 0x5F
    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 0x7F
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 0x9F
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 0xBF
    0,0,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
    2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2, // 0xDF
    3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3, // 0xEF
    4,4,4,4,4,0,0,0,0,0,0,0,0,0,0,0, // 0xFF
    ];

    /// Given a first byte, determine how many bytes are in this UTF-8 character
    #[inline]
    pub fn utf8_char_width(b: u8) -> usize {
        return UTF8_CHAR_WIDTH[b as usize] as usize;
    }

    /// Determines if a vector of `u16` contains valid UTF-16
    pub fn is_utf16(v: &[u16]) -> bool {
        let mut it = v.iter();
        macro_rules! next { ($ret:expr) => {
                match it.next() { Some(u) => *u, None => return $ret }
            }
        }
        loop {
            let u = next!(true);

            match char::from_u32(u as u32) {
                Some(_) => {}
                None => {
                    let u2 = next!(false);
                    if u < 0xD7FF || u > 0xDBFF || u2 < 0xDC00 || u2 > 0xDFFF {
                        return false;
                    }
                }
            }
        }
    }

    /// Iterator adaptor for encoding `char`s to UTF-16.
    #[derive(Clone)]
    pub struct Utf16Encoder<I> {
        chars: I,
        extra: u16,
    }

    impl<I> Utf16Encoder<I> {
        /// Create a UTF-16 encoder from any `char` iterator.
        pub fn new(chars: I) -> Utf16Encoder<I>
            where I: Iterator<Item = char>
        {
            Utf16Encoder {
                chars: chars,
                extra: 0,
            }
        }
    }

    impl<I> Iterator for Utf16Encoder<I>
        where I: Iterator<Item = char>
    {
        type Item = u16;

        #[inline]
        fn next(&mut self) -> Option<u16> {
            if self.extra != 0 {
                let tmp = self.extra;
                self.extra = 0;
                return Some(tmp);
            }

            self.chars.next().map(|ch| {
                let n = CharExt::encode_utf16(ch);
                let n = n.as_slice();
                if n.len() == 2 {
                    self.extra = n[1];
                }
                n[0]
            })
        }

        #[inline]
        fn size_hint(&self) -> (usize, Option<usize>) {
            let (low, high) = self.chars.size_hint();
            // every char gets either one u16 or two u16,
            // so this iterator is between 1 or 2 times as
            // long as the underlying iterator.
            (low, high.and_then(|n| n.checked_mul(2)))
        }
    }

    impl<'a> Iterator for SplitWhitespace<'a> {
        type Item = &'a str;

        fn next(&mut self) -> Option<&'a str> {
            self.inner.next()
        }
    }
    impl<'a> DoubleEndedIterator for SplitWhitespace<'a> {
        fn next_back(&mut self) -> Option<&'a str> {
            self.inner.next_back()
        }
    }

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