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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, FusedIterator};
    use core::str::Split;

    /// An iterator over the non-whitespace substrings of a string,
    /// separated by any amount of whitespace.
    ///
    /// This struct is created by the [`split_whitespace`] method on [`str`].
    /// See its documentation for more.
    ///
    /// [`split_whitespace`]: ../../std/primitive.str.html#method.split_whitespace
    /// [`str`]: ../../std/primitive.str.html
    #[stable(feature = "split_whitespace", since = "1.1.0")]
    #[derive(Clone, Debug)]
    pub struct SplitWhitespace<'a> {
        inner: Filter<Split<'a, IsWhitespace>, IsNotEmpty>,
    }

    /// Methods for Unicode string slices
    #[allow(missing_docs)] // docs in liballoc
    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 {
            SplitWhitespace { inner: self.split(IsWhitespace).filter(IsNotEmpty) }
        }

        #[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())
        }
    }

    /// 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,
                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);
            }

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

    #[unstable(feature = "fused", issue = "35602")]
    impl<I> FusedIterator for Utf16Encoder<I>
        where I: FusedIterator<Item = char> {}

    #[derive(Clone)]
    struct IsWhitespace;

    impl FnOnce<(char, )> for IsWhitespace {
        type Output = bool;

        #[inline]
        extern "rust-call" fn call_once(mut self, arg: (char, )) -> bool {
            self.call_mut(arg)
        }
    }

    impl FnMut<(char, )> for IsWhitespace {
        #[inline]
        extern "rust-call" fn call_mut(&mut self, arg: (char, )) -> bool {
            arg.0.is_whitespace()
        }
    }

    #[derive(Clone)]
    struct IsNotEmpty;

    impl<'a, 'b> FnOnce<(&'a &'b str, )> for IsNotEmpty {
        type Output = bool;

        #[inline]
        extern "rust-call" fn call_once(mut self, arg: (&&str, )) -> bool {
            self.call_mut(arg)
        }
    }

    impl<'a, 'b> FnMut<(&'a &'b str, )> for IsNotEmpty {
        #[inline]
        extern "rust-call" fn call_mut(&mut self, arg: (&&str, )) -> bool {
            !arg.0.is_empty()
        }
    }

    #[stable(feature = "split_whitespace", since = "1.1.0")]
    impl<'a> Iterator for SplitWhitespace<'a> {
        type Item = &'a str;

        fn next(&mut self) -> Option<&'a str> {
            self.inner.next()
        }
    }

    #[stable(feature = "split_whitespace", since = "1.1.0")]
    impl<'a> DoubleEndedIterator for SplitWhitespace<'a> {
        fn next_back(&mut self) -> Option<&'a str> {
            self.inner.next_back()
        }
    }

    #[unstable(feature = "fused", issue = "35602")]
    impl<'a> FusedIterator for SplitWhitespace<'a> {}

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