[libcxx] r210659 - Implement string_view from the library fundamentals TS (n4023). Also works in C++11 and 03, with reduced functionality (mostly in the area of constexpr)

Richard Smith richard at metafoo.co.uk
Wed Jun 11 15:56:28 PDT 2014


On Wed, Jun 11, 2014 at 9:44 AM, Marshall Clow <mclow.lists at gmail.com>
wrote:

> Author: marshall
> Date: Wed Jun 11 11:44:55 2014
> New Revision: 210659
>
> URL: http://llvm.org/viewvc/llvm-project?rev=210659&view=rev
> Log:
> Implement string_view from the library fundamentals TS (n4023). Also works
> in C++11 and 03, with reduced functionality (mostly in the area of
> constexpr)
>
 [...]

> Added: libcxx/trunk/include/experimental/string_view
> URL:
> http://llvm.org/viewvc/llvm-project/libcxx/trunk/include/experimental/string_view?rev=210659&view=auto
>
> ==============================================================================
> --- libcxx/trunk/include/experimental/string_view (added)
> +++ libcxx/trunk/include/experimental/string_view Wed Jun 11 11:44:55 2014
> @@ -0,0 +1,813 @@
> +// -*- C++ -*-
> +//===------------------------ string_view
> ---------------------------------===//
> +//
> +//                     The LLVM Compiler Infrastructure
> +//
> +// This file is distributed under the University of Illinois Open Source
> +// License. See LICENSE.TXT for details.
> +//
>
> +//===----------------------------------------------------------------------===//
> +
> +#ifndef _LIBCPP_LFTS_STRING_VIEW
> +#define _LIBCPP_LFTS_STRING_VIEW
> +
> +/*
> +string_view synopsis
> +
> +namespace std {
> + namespace experimental {
> +  inline namespace library_fundamentals_v1 {
> +
> +    // 7.2, Class template basic_string_view
> +    template<class charT, class traits = char_traits<charT>>
> +        class basic_string_view;
> +
> +    // 7.9, basic_string_view non-member comparison functions
> +    template<class charT, class traits>
> +    constexpr bool operator==(basic_string_view<charT, traits> x,
> +                              basic_string_view<charT, traits> y)
> noexcept;
> +    template<class charT, class traits>
> +    constexpr bool operator!=(basic_string_view<charT, traits> x,
> +                              basic_string_view<charT, traits> y)
> noexcept;
> +    template<class charT, class traits>
> +    constexpr bool operator< (basic_string_view<charT, traits> x,
> +                                 basic_string_view<charT, traits> y)
> noexcept;
> +    template<class charT, class traits>
> +    constexpr bool operator> (basic_string_view<charT, traits> x,
> +                              basic_string_view<charT, traits> y)
> noexcept;
> +    template<class charT, class traits>
> +    constexpr bool operator<=(basic_string_view<charT, traits> x,
> +                                 basic_string_view<charT, traits> y)
> noexcept;
> +    template<class charT, class traits>
> +    constexpr bool operator>=(basic_string_view<charT, traits> x,
> +                              basic_string_view<charT, traits> y)
> noexcept;
> +    // see below, sufficient additional overloads of comparison functions
> +
> +    // 7.10, Inserters and extractors
> +    template<class charT, class traits>
> +      basic_ostream<charT, traits>&
> +        operator<<(basic_ostream<charT, traits>& os,
> +                   basic_string_view<charT, traits> str);
> +
> +    // basic_string_view typedef names
> +    typedef basic_string_view<char> string_view;
> +    typedef basic_string_view<char16_t> u16string_view;
> +    typedef basic_string_view<char32_t> u32string_view;
> +    typedef basic_string_view<wchar_t> wstring_view;
> +
> +  }  // namespace fundamentals_v1
> + }  // namespace experimental
> +
> +  // 7.11, Hash support
> +  template <class T> struct hash;
> +  template <> struct hash<experimental::string_view>;
> +  template <> struct hash<experimental::u16string_view>;
> +  template <> struct hash<experimental::u32string_view>;
> +  template <> struct hash<experimental::wstring_view>;
> +
> +}  // namespace std
> +
> +
> +template<class charT, class traits = char_traits<charT>>
> +class basic_string_view {
>

[Nit: missing std::experimental::library_fundamentals_v1 here. Also, I
think we usually put this part of the comment inside the first declaration
rather than splitting it out like the standard does.]


> +  public:
> +  // types
> +  typedef traits traits_type;
> +  typedef charT value_type;
> +  typedef charT* pointer;
> +  typedef const charT* const_pointer;
> +  typedef charT& reference;
> +  typedef const charT& const_reference;
> +  typedef implementation-defined const_iterator; // See 7.4
>

Should this comment be here?


> +  typedef const_iterator iterator;22) Because basic_string_view refers to
> a constant sequence, iterator and const_iterator are the same type.
>

Should this footnote be here?


> +  typedef reverse_iterator<const_iterator> const_reverse_iterator;
> +  typedef const_reverse_iterator reverse_iterator;
> +  typedef size_t size_type;
> +  typedef ptrdiff_t difference_type;
> +  static constexpr size_type npos = size_type(-1);
> +
> +  // 7.3, basic_string_view constructors and assignment operators
> +  constexpr basic_string_view() noexcept;
> +  constexpr basic_string_view(const basic_string_view&) noexcept =
> default;
> +  basic_string_view& operator=(const basic_string_view&) noexcept =
> default;
> +  template<class Allocator>
> +  basic_string_view(const basic_string<charT, traits, Allocator>& str)
> noexcept;
> +  constexpr basic_string_view(const charT* str);
> +  constexpr basic_string_view(const charT* str, size_type len);
> +
> +  // 7.4, basic_string_view iterator support
> +  constexpr const_iterator begin() const noexcept;
> +  constexpr const_iterator end() const noexcept;
> +  constexpr const_iterator cbegin() const noexcept;
> +  constexpr const_iterator cend() const noexcept;
> +  const_reverse_iterator rbegin() const noexcept;
> +  const_reverse_iterator rend() const noexcept;
> +  const_reverse_iterator crbegin() const noexcept;
> +  const_reverse_iterator crend() const noexcept;
> +
> +  // 7.5, basic_string_view capacity
> +  constexpr size_type size() const noexcept;
> +  constexpr size_type length() const noexcept;
> +  constexpr size_type max_size() const noexcept;
> +  constexpr bool empty() const noexcept;
> +
> +  // 7.6, basic_string_view element access
> +  constexpr const_reference operator[](size_type pos) const;
> +  constexpr const_reference at(size_type pos) const;
> +  constexpr const_reference front() const;
> +  constexpr const_reference back() const;
> +  constexpr const_pointer data() const noexcept;
> +
> +  // 7.7, basic_string_view modifiers
> +  constexpr void clear() noexcept;
> +  constexpr void remove_prefix(size_type n);
> +  constexpr void remove_suffix(size_type n);
> +  constexpr void swap(basic_string_view& s) noexcept;
> +
> +  // 7.8, basic_string_view string operations
> +  template<class Allocator>
> +  explicit operator basic_string<charT, traits, Allocator>() const;
> +  template<class Allocator = allocator<charT>>
> +  basic_string<charT, traits, Allocator> to_string(
> +    const Allocator& a = Allocator()) const;
> +
> +  size_type copy(charT* s, size_type n, size_type pos = 0) const;
> +
> +  constexpr basic_string_view substr(size_type pos = 0, size_type n =
> npos) const;
> +  constexpr int compare(basic_string_view s) const noexcept;
> +  constexpr int compare(size_type pos1, size_type n1, basic_string_view
> s) const;
> +  constexpr int compare(size_type pos1, size_type n1,
> +                        basic_string_view s, size_type pos2, size_type
> n2) const;
> +  constexpr int compare(const charT* s) const;
> +  constexpr int compare(size_type pos1, size_type n1, const charT* s)
> const;
> +  constexpr int compare(size_type pos1, size_type n1,
> +                        const charT* s, size_type n2) const;
> +  constexpr size_type find(basic_string_view s, size_type pos = 0) const
> noexcept;
> +  constexpr size_type find(charT c, size_type pos = 0) const noexcept;
> +  constexpr size_type find(const charT* s, size_type pos, size_type n)
> const;
> +  constexpr size_type find(const charT* s, size_type pos = 0) const;
> +  constexpr size_type rfind(basic_string_view s, size_type pos = npos)
> const noexcept;
> +  constexpr size_type rfind(charT c, size_type pos = npos) const noexcept;
> +  constexpr size_type rfind(const charT* s, size_type pos, size_type n)
> const;
> +  constexpr size_type rfind(const charT* s, size_type pos = npos) const;
> +  constexpr size_type find_first_of(basic_string_view s, size_type pos =
> 0) const noexcept;
> +  constexpr size_type find_first_of(charT c, size_type pos = 0) const
> noexcept;
> +  constexpr size_type find_first_of(const charT* s, size_type pos,
> size_type n) const;
> +  constexpr size_type find_first_of(const charT* s, size_type pos = 0)
> const;
> +  constexpr size_type find_last_of(basic_string_view s, size_type pos =
> npos) const noexcept;
> +  constexpr size_type find_last_of(charT c, size_type pos = npos) const
> noexcept;
> +  constexpr size_type find_last_of(const charT* s, size_type pos,
> size_type n) const;
> +  constexpr size_type find_last_of(const charT* s, size_type pos = npos)
> const;
> +  constexpr size_type find_first_not_of(basic_string_view s, size_type
> pos = 0) const noexcept;
> +  constexpr size_type find_first_not_of(charT c, size_type pos = 0) const
> noexcept;
> +  constexpr size_type find_first_not_of(const charT* s, size_type pos,
> size_type n) const;
> +  constexpr size_type find_first_not_of(const charT* s, size_type pos =
> 0) const;
> +  constexpr size_type find_last_not_of(basic_string_view s, size_type pos
> = npos) const noexcept;
> +  constexpr size_type find_last_not_of(charT c, size_type pos = npos)
> const noexcept;
> +  constexpr size_type find_last_not_of(const charT* s, size_type pos,
> size_type n) const;
> +  constexpr size_type find_last_not_of(const charT* s, size_type pos =
> npos) const;
> +
> + private:
> +  const_pointer data_;  // exposition only
> +  size_type     size_;  // exposition only
> +};
> +
> +
> +*/
> +
> +#include <__config>
> +
> +#include <string>
> +#include <algorithm>
> +#include <iterator>
> +#include <ostream>
> +#include <iomanip>
> +
> +#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
> +#pragma GCC system_header
> +#endif
> +
> +namespace std {
> + namespace experimental {
> +  inline namespace library_fundamentals_v1 {
> +
> +    template<class _CharT, class _Traits = _VSTD::char_traits<_CharT> >
> +    class _LIBCPP_TYPE_VIS_ONLY basic_string_view {
> +    public:
> +        // types
> +        typedef _Traits                                    traits_type;
> +        typedef _CharT                                     value_type;
> +        typedef const _CharT*                              pointer;
> +        typedef const _CharT*                              const_pointer;
> +        typedef const _CharT&                              reference;
> +        typedef const _CharT&
>  const_reference;
> +        typedef const_pointer
>  const_iterator; // See [string.view.iterators]
> +        typedef const_iterator                             iterator;
> +        typedef _VSTD::reverse_iterator<const_iterator>
>  const_reverse_iterator;
> +        typedef const_reverse_iterator
> reverse_iterator;
> +        typedef size_t                                     size_type;
> +        typedef ptrdiff_t
>  difference_type;
> +        static _LIBCPP_CONSTEXPR const size_type npos = -1; //
> size_type(-1);
> +
> +        // [string.view.cons], construct/copy
> +        _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
> +        basic_string_view() _NOEXCEPT : __data (nullptr), __size(0) {}
> +
> +        _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
> +        basic_string_view(const basic_string_view&) _NOEXCEPT = default;
> +
> +        _LIBCPP_INLINE_VISIBILITY
> +        basic_string_view& operator=(const basic_string_view&) _NOEXCEPT
> = default;
> +
> +        template<class _Allocator>
> +        _LIBCPP_INLINE_VISIBILITY
> +        basic_string_view(const basic_string<_CharT, _Traits,
> _Allocator>& __str) _NOEXCEPT
> +            : __data (__str.data()), __size(__str.size()) {}
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        basic_string_view(const _CharT* __s, size_type __len)
> +            : __data(__s), __size(__len)
> +        {
> +            _LIBCPP_ASSERT(__len == 0 || __s != nullptr,
> "string_view::string_view(_CharT *, size_t): recieved nullptr");
>

You could make this constexpr even in C++11 by moving this check into one
of the member initializers. I think this is an important function to make
constexpr.

+        }
> +
> +        _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
> +        basic_string_view(const _CharT* __s)
> +            : __data(__s), __size(_Traits::length(__s)) {}
> +
> +        // [string.view.iterators], iterators
> +        _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
> +        const_iterator begin()  const _NOEXCEPT { return cbegin(); }
> +
> +        _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
> +        const_iterator end()    const _NOEXCEPT { return cend(); }
> +
> +        _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
> +        const_iterator cbegin() const _NOEXCEPT { return __data; }
> +
> +        _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
> +        const_iterator cend()   const _NOEXCEPT { return __data + __size;
> }
> +
> +        _LIBCPP_INLINE_VISIBILITY
> +        const_reverse_iterator rbegin()   const _NOEXCEPT { return
> const_reverse_iterator(cend()); }
> +
> +        _LIBCPP_INLINE_VISIBILITY
> +        const_reverse_iterator rend()     const _NOEXCEPT { return
> const_reverse_iterator(cbegin()); }
> +
> +        _LIBCPP_INLINE_VISIBILITY
> +        const_reverse_iterator crbegin()  const _NOEXCEPT { return
> const_reverse_iterator(cend()); }
> +
> +        _LIBCPP_INLINE_VISIBILITY
> +        const_reverse_iterator crend()    const _NOEXCEPT { return
> const_reverse_iterator(cbegin()); }
> +
> +        // [string.view.capacity], capacity
> +        _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
> +        size_type size()     const _NOEXCEPT { return __size; }
> +
> +        _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
> +        size_type length()   const _NOEXCEPT { return __size; }
> +
> +        _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
> +        size_type max_size() const _NOEXCEPT { return
> _VSTD::numeric_limits<size_type>::max(); }
> +
> +        _LIBCPP_CONSTEXPR bool _LIBCPP_INLINE_VISIBILITY
> +        empty()         const _NOEXCEPT { return __size == 0; }
> +
> +        // [string.view.access], element access
> +        _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
> +        const_reference operator[](size_type __pos) const { return
> __data[__pos]; }
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        const_reference at(size_type __pos) const
> +        {
> +            if (__pos >= size())
> +                throw out_of_range("string_view::at");
> +            return __data[__pos];
>

You can make this one constexpr in c++11 with

  return __data[__pos >= size() ? throw out_of_range(...) : __pos];

+        }
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        const_reference front() const
> +        {
> +            _LIBCPP_ASSERT(!empty(), "string_view::front(): string is
> empty");
> +            return __data[0];
> +        }
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        const_reference back() const
> +        {
> +            _LIBCPP_ASSERT(!empty(), "string_view::back(): string is
> empty");
> +            return __data[__size-1];
> +        }
>

You can do similar things here.

+        _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
> +        const_pointer data() const _NOEXCEPT { return __data; }
> +
> +        // [string.view.modifiers], modifiers:
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        void clear() _NOEXCEPT
> +        {
> +            __data = nullptr;
> +            __size = 0;
> +        }
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        void remove_prefix(size_type __n) _NOEXCEPT
> +        {
> +            if (__n > __size)
> +                __n = __size;
> +            __data += __n;
> +            __size -= __n;
> +        }
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        void remove_suffix(size_type __n) _NOEXCEPT
> +        {
> +            if (__n > __size)
> +                __n = __size;
> +            __size -= __n;
> +        }
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        void swap(basic_string_view& __other) _NOEXCEPT
> +        {
> +               const value_type *__p = __data;
> +               __data = __other.__data;
> +               __other.__data = __p;
> +
> +               size_type __sz = __size;
> +               __size = __other.__size;
> +               __other.__size = __sz;
> +//             _VSTD::swap( __data, __other.__data );
> +//             _VSTD::swap( __size, __other.__size );
> +        }
>

Would it make sense to provide a _LIBCPP_CONSTEXPR_AFTER_CXX11
_VSTD::__swap for use in places like this?


> +        // [string.view.ops], string operations:
> +        template<class _Allocator>
> +        _LIBCPP_INLINE_VISIBILITY
> +        _LIBCPP_EXPLICIT operator basic_string<_CharT, _Traits,
> _Allocator>() const
> +        { return basic_string<_CharT, _Traits, _Allocator>( begin(),
> end()); }
> +
> +        template<class _Allocator = allocator<_CharT> >
> +        _LIBCPP_INLINE_VISIBILITY
> +        basic_string<_CharT, _Traits, _Allocator> to_string( const
> _Allocator& __a = _Allocator())
> +        { return basic_string<_CharT, _Traits, _Allocator> ( begin(),
> end(), __a ); }
> +
> +        size_type copy(_CharT* __s, size_type __n, size_type __pos = 0)
> const
> +        {
> +            if ( __pos > size())
> +                throw out_of_range("string_view::copy");
> +            size_type __rlen = _VSTD::min( __n, size() - __pos );
> +            _VSTD::copy_n(begin() + __pos, __rlen, __s );
> +            return __rlen;
> +        }
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 basic_string_view substr(size_type
> __pos = 0, size_type __n = npos) const
> +        {
> +            if (__pos > size())
> +                throw out_of_range("string_view::substr");
> +            size_type __rlen = _VSTD::min( __n, size() - __pos );
> +            return basic_string_view(data() + __pos, __rlen);
> +        }
>

It also seems like it would be worth making this work in C++11.

+        _LIBCPP_CONSTEXPR_AFTER_CXX11 int compare(basic_string_view __sv)
> const _NOEXCEPT
> +        {
> +            size_type __rlen = _VSTD::min( size(), __sv.size());
> +            int __retval = _Traits::compare(data(), __sv.data(), __rlen);
> +            if ( __retval == 0 ) // first __rlen chars matched
> +                __retval = size() == __sv.size() ? 0 : ( size() <
> __sv.size() ? -1 : 1 );
> +            return __retval;
> +        }
> +
> +        _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
> +        int compare(size_type __pos1, size_type __n1, basic_string_view
> __sv) const
> +        {
> +            return substr(__pos1, __n1).compare(__sv);
> +        }
> +
> +        _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
> +        int compare(                       size_type __pos1, size_type
> __n1,
> +                    basic_string_view _sv, size_type __pos2, size_type
> __n2) const
> +        {
> +            return substr(__pos1, __n1).compare(_sv.substr(__pos2, __n2));
> +        }
> +
> +        _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
> +        int compare(const _CharT* __s) const
> +        {
> +            return compare(basic_string_view(__s));
> +        }
> +
> +        _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
> +        int compare(size_type __pos1, size_type __n1, const _CharT* __s)
> const
> +        {
> +            return substr(__pos1, __n1).compare(basic_string_view(__s));
> +        }
> +
> +        _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
> +        int compare(size_type __pos1, size_type __n1, const _CharT* __s,
> size_type __n2) const
> +        {
> +            return substr(__pos1, __n1).compare(basic_string_view(__s,
> __n2));
> +        }
>

The preceding 5 functions should be CONSTEXPR_AFTER_CXX11, since they can
never be used in constant expressions in C++11 (they unconditionally call
the first 'compare', which is not constexpr in C++11). This code is
ill-formed, no diagnostic required.

+        // find
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        size_type find(basic_string_view __s, size_type __pos = 0) const
> _NOEXCEPT
> +        {
> +            _LIBCPP_ASSERT(__s.size() == 0 || __s.data() != nullptr,
> "string_view::find(): recieved nullptr");
> +            return _VSTD::__str_find<value_type, size_type, traits_type,
> npos>
> +                (data(), size(), __s.data(), __pos, __s.size());
> +        }
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        size_type find(_CharT __c, size_type __pos = 0) const _NOEXCEPT
> +        {
> +            return _VSTD::__str_find<value_type, size_type, traits_type,
> npos>
> +                (data(), size(), __c, __pos);
> +        }
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        size_type find(const _CharT* __s, size_type __pos, size_type __n)
> const
> +        {
> +            _LIBCPP_ASSERT(__n == 0 || __s != nullptr,
> "string_view::find(): recieved nullptr");
> +            return _VSTD::__str_find<value_type, size_type, traits_type,
> npos>
> +                (data(), size(), __s, __pos, __n);
> +        }
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        size_type find(const _CharT* __s, size_type __pos = 0) const
> +        {
> +            _LIBCPP_ASSERT(__s != nullptr, "string_view::find(): recieved
> nullptr");
> +            return _VSTD::__str_find<value_type, size_type, traits_type,
> npos>
> +                (data(), size(), __s, __pos, traits_type::length(__s));
> +        }
> +
> +        // rfind
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        size_type rfind(basic_string_view __s, size_type __pos = npos)
> const _NOEXCEPT
> +        {
> +            _LIBCPP_ASSERT(__s.size() == 0 || __s.data() != nullptr,
> "string_view::find(): recieved nullptr");
> +            return _VSTD::__str_rfind<value_type, size_type, traits_type,
> npos>
> +                (data(), size(), __s.data(), __pos, __s.size());
> +        }
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        size_type rfind(_CharT __c, size_type __pos = npos) const
> _NOEXCEPT
> +        {
> +            return _VSTD::__str_rfind<value_type, size_type, traits_type,
> npos>
> +                (data(), size(), __c, __pos);
> +        }
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        size_type rfind(const _CharT* __s, size_type __pos, size_type
> __n) const
> +        {
> +            _LIBCPP_ASSERT(__n == 0 || __s != nullptr,
> "string_view::rfind(): recieved nullptr");
> +            return _VSTD::__str_rfind<value_type, size_type, traits_type,
> npos>
> +                (data(), size(), __s, __pos, __n);
> +        }
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        size_type rfind(const _CharT* __s, size_type __pos=npos) const
> +        {
> +            _LIBCPP_ASSERT(__s != nullptr, "string_view::rfind():
> recieved nullptr");
> +            return _VSTD::__str_rfind<value_type, size_type, traits_type,
> npos>
> +                (data(), size(), __s, __pos, traits_type::length(__s));
> +        }
> +
> +        // find_first_of
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        size_type find_first_of(basic_string_view __s, size_type __pos =
> 0) const _NOEXCEPT
> +        {
> +            _LIBCPP_ASSERT(__s.size() == 0 || __s.data() != nullptr,
> "string_view::find_first_of(): recieved nullptr");
> +            return _VSTD::__str_find_first_of<value_type, size_type,
> traits_type, npos>
> +                (data(), size(), __s.data(), __pos, __s.size());
> +        }
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        size_type find_first_of(_CharT __c, size_type __pos = 0) const
> _NOEXCEPT
> +        { return find(__c, __pos); }
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        size_type find_first_of(const _CharT* __s, size_type __pos,
> size_type __n) const
> +        {
> +            _LIBCPP_ASSERT(__n == 0 || __s != nullptr,
> "string_view::find_first_of(): recieved nullptr");
> +            return _VSTD::__str_find_first_of<value_type, size_type,
> traits_type, npos>
> +                (data(), size(), __s, __pos, __n);
> +        }
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        size_type find_first_of(const _CharT* __s, size_type __pos=0)
> const
> +        {
> +            _LIBCPP_ASSERT(__s != nullptr, "string_view::find_first_of():
> recieved nullptr");
> +            return _VSTD::__str_find_first_of<value_type, size_type,
> traits_type, npos>
> +                (data(), size(), __s, __pos, traits_type::length(__s));
> +        }
> +
> +        // find_last_of
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        size_type find_last_of(basic_string_view __s, size_type
> __pos=npos) const _NOEXCEPT
> +        {
> +            _LIBCPP_ASSERT(__s.size() == 0 || __s.data() != nullptr,
> "string_view::find_last_of(): recieved nullptr");
> +            return _VSTD::__str_find_last_of<value_type, size_type,
> traits_type, npos>
> +                (data(), size(), __s.data(), __pos, __s.size());
> +        }
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        size_type find_last_of(_CharT __c, size_type __pos = npos) const
> _NOEXCEPT
> +        { return rfind(__c, __pos); }
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        size_type find_last_of(const _CharT* __s, size_type __pos,
> size_type __n) const
> +        {
> +            _LIBCPP_ASSERT(__n == 0 || __s != nullptr,
> "string_view::find_last_of(): recieved nullptr");
> +            return _VSTD::__str_find_last_of<value_type, size_type,
> traits_type, npos>
> +                (data(), size(), __s, __pos, __n);
> +        }
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        size_type find_last_of(const _CharT* __s, size_type __pos=npos)
> const
> +        {
> +            _LIBCPP_ASSERT(__s != nullptr, "string_view::find_last_of():
> recieved nullptr");
> +            return _VSTD::__str_find_last_of<value_type, size_type,
> traits_type, npos>
> +                (data(), size(), __s, __pos, traits_type::length(__s));
> +        }
> +
> +        // find_first_not_of
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        size_type find_first_not_of(basic_string_view __s, size_type
> __pos=0) const _NOEXCEPT
> +        {
> +            _LIBCPP_ASSERT(__s.size() == 0 || __s.data() != nullptr,
> "string_view::find_first_not_of(): recieved nullptr");
> +            return _VSTD::__str_find_first_not_of<value_type, size_type,
> traits_type, npos>
> +                (data(), size(), __s.data(), __pos, __s.size());
> +        }
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        size_type find_first_not_of(_CharT __c, size_type __pos=0) const
> _NOEXCEPT
> +        {
> +            return _VSTD::__str_find_first_not_of<value_type, size_type,
> traits_type, npos>
> +                (data(), size(), __c, __pos);
> +        }
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        size_type find_first_not_of(const _CharT* __s, size_type __pos,
> size_type __n) const
> +        {
> +            _LIBCPP_ASSERT(__n == 0 || __s != nullptr,
> "string_view::find_first_not_of(): recieved nullptr");
> +            return _VSTD::__str_find_first_not_of<value_type, size_type,
> traits_type, npos>
> +                (data(), size(), __s, __pos, __n);
> +        }
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        size_type find_first_not_of(const _CharT* __s, size_type __pos=0)
> const
> +        {
> +            _LIBCPP_ASSERT(__s != nullptr,
> "string_view::find_first_not_of(): recieved nullptr");
> +            return _VSTD::__str_find_first_not_of<value_type, size_type,
> traits_type, npos>
> +                (data(), size(), __s, __pos, traits_type::length(__s));
> +        }
> +
> +        // find_last_not_of
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        size_type find_last_not_of(basic_string_view __s, size_type
> __pos=npos) const _NOEXCEPT
> +        {
> +            _LIBCPP_ASSERT(__s.size() == 0 || __s.data() != nullptr,
> "string_view::find_last_not_of(): recieved nullptr");
> +            return _VSTD::__str_find_last_not_of<value_type, size_type,
> traits_type, npos>
> +                (data(), size(), __s.data(), __pos, __s.size());
> +        }
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        size_type find_last_not_of(_CharT __c, size_type __pos=npos)
> const _NOEXCEPT
> +        {
> +            return _VSTD::__str_find_last_not_of<value_type, size_type,
> traits_type, npos>
> +                (data(), size(), __c, __pos);
> +        }
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        size_type find_last_not_of(const _CharT* __s, size_type __pos,
> size_type __n) const
> +        {
> +            _LIBCPP_ASSERT(__n == 0 || __s != nullptr,
> "string_view::find_last_not_of(): recieved nullptr");
> +            return _VSTD::__str_find_last_not_of<value_type, size_type,
> traits_type, npos>
> +                (data(), size(), __s, __pos, __n);
> +        }
> +
> +        _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +        size_type find_last_not_of(const _CharT* __s, size_type
> __pos=npos) const
> +        {
> +            _LIBCPP_ASSERT(__s != nullptr,
> "string_view::find_last_not_of(): recieved nullptr");
> +            return _VSTD::__str_find_last_not_of<value_type, size_type,
> traits_type, npos>
> +                (data(), size(), __s, __pos, traits_type::length(__s));
> +        }
> +
> +    private:
> +        const   value_type* __data;
> +        size_type           __size;
> +    };
> +
> +
> +    // [string.view.comparison]
> +    // operator ==
> +    template<class _CharT, class _Traits>
> +    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +    bool operator==(basic_string_view<_CharT, _Traits> __lhs,
> +                    basic_string_view<_CharT, _Traits> __rhs) _NOEXCEPT
> +    {
> +        if ( __lhs.size() != __rhs.size()) return false;
> +        return __lhs.compare(__rhs) == 0;
> +    }
> +
> +    template<class _CharT, class _Traits>
> +    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +    bool operator==(basic_string_view<_CharT, _Traits> __lhs,
> +                    typename _VSTD::common_type<basic_string_view<_CharT,
> _Traits> >::type __rhs) _NOEXCEPT
>

Seems weird that we use common_type, not identity, here. Is there some
subtly to this, beyond merely creating a non-deduced context?

+    {
> +        if ( __lhs.size() != __rhs.size()) return false;
> +        return __lhs.compare(__rhs) == 0;
> +    }
> +
> +    template<class _CharT, class _Traits>
> +    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +    bool operator==(typename _VSTD::common_type<basic_string_view<_CharT,
> _Traits> >::type __lhs,
> +                    basic_string_view<_CharT, _Traits> __rhs) _NOEXCEPT
> +    {
> +        if ( __lhs.size() != __rhs.size()) return false;
> +        return __lhs.compare(__rhs) == 0;
> +    }
> +
> +
> +    // operator !=
> +    template<class _CharT, class _Traits>
> +    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +    bool operator!=(basic_string_view<_CharT, _Traits> __lhs,
> basic_string_view<_CharT, _Traits> __rhs) _NOEXCEPT
> +    {
> +        if ( __lhs.size() != __rhs.size())
> +            return true;
> +        return __lhs.compare(__rhs) != 0;
> +    }
> +
> +    template<class _CharT, class _Traits>
> +    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +    bool operator!=(basic_string_view<_CharT, _Traits> __lhs,
> +                    typename _VSTD::common_type<basic_string_view<_CharT,
> _Traits> >::type __rhs) _NOEXCEPT
> +    {
> +        if ( __lhs.size() != __rhs.size())
> +            return true;
> +        return __lhs.compare(__rhs) != 0;
> +    }
> +
> +    template<class _CharT, class _Traits>
> +    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +    bool operator!=(typename _VSTD::common_type<basic_string_view<_CharT,
> _Traits> >::type __lhs,
> +                    basic_string_view<_CharT, _Traits> __rhs) _NOEXCEPT
> +    {
> +        if ( __lhs.size() != __rhs.size())
> +            return true;
> +        return __lhs.compare(__rhs) != 0;
> +    }
> +
> +
> +    // operator <
> +    template<class _CharT, class _Traits>
> +    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +    bool operator<(basic_string_view<_CharT, _Traits> __lhs,
> basic_string_view<_CharT, _Traits> __rhs) _NOEXCEPT
> +    {
> +        return __lhs.compare(__rhs) < 0;
> +    }
> +
> +    template<class _CharT, class _Traits>
> +    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +    bool operator<(basic_string_view<_CharT, _Traits> __lhs,
> +                    typename _VSTD::common_type<basic_string_view<_CharT,
> _Traits> >::type __rhs) _NOEXCEPT
> +    {
> +        return __lhs.compare(__rhs) < 0;
> +    }
> +
> +    template<class _CharT, class _Traits>
> +    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +    bool operator<(typename _VSTD::common_type<basic_string_view<_CharT,
> _Traits> >::type __lhs,
> +                    basic_string_view<_CharT, _Traits> __rhs) _NOEXCEPT
> +    {
> +        return __lhs.compare(__rhs) < 0;
> +    }
> +
> +
> +    // operator >
> +    template<class _CharT, class _Traits>
> +    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +    bool operator> (basic_string_view<_CharT, _Traits> __lhs,
> basic_string_view<_CharT, _Traits> __rhs) _NOEXCEPT
> +    {
> +        return __lhs.compare(__rhs) > 0;
> +    }
> +
> +    template<class _CharT, class _Traits>
> +    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +    bool operator>(basic_string_view<_CharT, _Traits> __lhs,
> +                    typename _VSTD::common_type<basic_string_view<_CharT,
> _Traits> >::type __rhs) _NOEXCEPT
> +    {
> +        return __lhs.compare(__rhs) > 0;
> +    }
> +
> +    template<class _CharT, class _Traits>
> +    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +    bool operator>(typename _VSTD::common_type<basic_string_view<_CharT,
> _Traits> >::type __lhs,
> +                    basic_string_view<_CharT, _Traits> __rhs) _NOEXCEPT
> +    {
> +        return __lhs.compare(__rhs) > 0;
> +    }
> +
> +
> +    // operator <=
> +    template<class _CharT, class _Traits>
> +    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +    bool operator<=(basic_string_view<_CharT, _Traits> __lhs,
> basic_string_view<_CharT, _Traits> __rhs) _NOEXCEPT
> +    {
> +        return __lhs.compare(__rhs) <= 0;
> +    }
> +
> +    template<class _CharT, class _Traits>
> +    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +    bool operator<=(basic_string_view<_CharT, _Traits> __lhs,
> +                    typename _VSTD::common_type<basic_string_view<_CharT,
> _Traits> >::type __rhs) _NOEXCEPT
> +    {
> +        return __lhs.compare(__rhs) <= 0;
> +    }
> +
> +    template<class _CharT, class _Traits>
> +    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +    bool operator<=(typename _VSTD::common_type<basic_string_view<_CharT,
> _Traits> >::type __lhs,
> +                    basic_string_view<_CharT, _Traits> __rhs) _NOEXCEPT
> +    {
> +        return __lhs.compare(__rhs) <= 0;
> +    }
> +
> +
> +    // operator >=
> +    template<class _CharT, class _Traits>
> +    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +    bool operator>=(basic_string_view<_CharT, _Traits> __lhs,
> basic_string_view<_CharT, _Traits> __rhs) _NOEXCEPT
> +    {
> +        return __lhs.compare(__rhs) >= 0;
> +    }
> +
> +
> +    template<class _CharT, class _Traits>
> +    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +    bool operator>=(basic_string_view<_CharT, _Traits> __lhs,
> +                    typename _VSTD::common_type<basic_string_view<_CharT,
> _Traits> >::type __rhs) _NOEXCEPT
> +    {
> +        return __lhs.compare(__rhs) >= 0;
> +    }
> +
> +    template<class _CharT, class _Traits>
> +    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
> +    bool operator>=(typename _VSTD::common_type<basic_string_view<_CharT,
> _Traits> >::type __lhs,
> +                    basic_string_view<_CharT, _Traits> __rhs) _NOEXCEPT
> +    {
> +        return __lhs.compare(__rhs) >= 0;
> +    }
> +
> +
> +    // [string.view.io]
> +    template<class _CharT, class _Traits>
> +    basic_ostream<_CharT, _Traits>&
> +    operator<<(basic_ostream<_CharT, _Traits>& __os,
> basic_string_view<_CharT, _Traits> __sv)
> +    {
> +        return _VSTD::__put_character_sequence(__os, __sv.data(),
> __sv.size());
> +    }
> +
> +  typedef basic_string_view<char>     string_view;
> +  typedef basic_string_view<char16_t> u16string_view;
> +  typedef basic_string_view<char32_t> u32string_view;
> +  typedef basic_string_view<wchar_t>  wstring_view;
> +
> +}}}  // close std::experimental::library_fundamentals_v1
> +
> +_LIBCPP_BEGIN_NAMESPACE_STD
> +
> +// [string.view.hash]
> +// Shamelessly stolen from <string>
> +template<class _CharT, class _Traits>
> +struct _LIBCPP_TYPE_VIS_ONLY
> hash<std::experimental::basic_string_view<_CharT, _Traits> >
> +    : public unary_function<std::experimental::basic_string_view<_CharT,
> _Traits>, size_t>
> +{
> +    size_t operator()(const std::experimental::basic_string_view<_CharT,
> _Traits>& __val) const _NOEXCEPT;
> +};
> +
> +template<class _CharT, class _Traits>
> +size_t
> +hash<std::experimental::basic_string_view<_CharT, _Traits> >::operator()(
> +        const std::experimental::basic_string_view<_CharT, _Traits>&
> __val) const _NOEXCEPT
> +{
> +    return __do_string_hash(__val.data(), __val.data() + __val.size());
> +}
> +
> +#if _LIBCPP_STD_VER > 11
> +template <class _CharT, class _Traits>
> +__quoted_output_proxy<_CharT, const _CharT *, _Traits>
> +quoted ( std::experimental::basic_string_view <_CharT, _Traits> __sv,
> +             _CharT __delim = _CharT('"'), _CharT __escape=_CharT('\\'))
> +{
> +    return __quoted_output_proxy<_CharT, const _CharT *, _Traits>
> +         ( __sv.data(), __sv.data() + __sv.size(), __delim, __escape );
> +}
> +#endif
> +
> +_LIBCPP_END_NAMESPACE_STD
> +
> +#endif // _LIBCPP_LFTS_STRING_VIEW
>
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