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 //
 // process/environment.hpp
 // ~~~~~~~~~~~~~~~~~~~~~~~~
 //
 // Copyright (c) 2021 Klemens D. Morgenstern (klemens dot morgenstern at gmx dot net)
 //
 // Distributed under the Boost Software License, Version 1.0. (See accompanying
 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 
 #ifndef BOOST_PROCESS_V2_ENVIRONMENT_HPP
 #define BOOST_PROCESS_V2_ENVIRONMENT_HPP
 
 #include <boost/process/v2/detail/config.hpp>
 #include <boost/process/v2/cstring_ref.hpp>
 #include <boost/process/v2/detail/utf8.hpp>
 #include <boost/type_traits.hpp>
 #include <functional>
 #include <memory>
 #include <numeric>
 
 #if !defined(GENERATING_DOCUMENTATION)
 #if defined(BOOST_PROCESS_V2_WINDOWS)
 #include <boost/process/v2/detail/environment_win.hpp>
 #else
 #include <boost/process/v2/detail/environment_posix.hpp>
 #endif
 #endif
 
 BOOST_PROCESS_V2_BEGIN_NAMESPACE
 
 /// Namespace for information and functions regarding the calling process.
 namespace environment
 {
 
 #if defined(GENERATING_DOCUMENTATION)
 
 /// A char traits type that reflects the OS rules for string representing environment keys.
 /** Can be an alias of std::char_traits. May only be defined for `char` and `wchar_t`.
  * 
  * Windows treats keys as case-insensitive yet perserving. The char traits are made to reflect 
  * that behaviour.
 */
 tempalte<typename Char>
 using key_char_traits = implementation_defined ;
 
 /// A char traits type that reflects the OS rules for string representing environment values.
 /** Can be an alias of std::char_traits. May only be defined for `char` and `wchar_t`.
 */
 tempalte<typename Char>
 using value_char_traits = implementation_defined ;
 
 /// The character type used by the environment. Either `char` or `wchar_t`.
 using char_type = implementation_defined ;
 
 /// The equal character in an environment string used to separate key and value.
 constexpr char_type equality_sign = implementation_defined;
 
 /// The delimiter in environemtn lists. Commonly used by the `PATH` variable.
 constexpr char_type delimiter = implementation_defined;
 
 /// The native handle of an environment. Note that this can be an owning pointer and is generally not thread safe.
 using native_handle = implementation_defined;
 
 
 #endif
 
 
 /// The iterator used by a value or value_view to iterator through environments that are lists.
 struct value_iterator
 {
     using string_view_type  = basic_string_view<char_type, value_char_traits<char_type>>;
     using difference_type   = int;
     using reference         = string_view_type;
     using iterator_category = std::forward_iterator_tag;
 
     value_iterator & operator++()
     {
         const auto delim = view_.find(delimiter);
         if (delim != string_view_type::npos)
           view_ = view_.substr(delim + 1);
         else
           view_ = view_.substr(view_.size());
         return *this;
     }
 
     value_iterator operator++(int)
     {
         auto last = *this;
         ++(*this);
         return last;
     }
     string_view_type operator*() const
     {
       const auto delim = view_.find(delimiter);
       if (delim == string_view_type::npos)
         return view_;
       else
         return view_.substr(0, delim);
     }
 
     value_iterator() = default;
     value_iterator(const value_iterator & ) = default;
     value_iterator(string_view_type view, std::size_t offset = 0u) : view_(view.substr(offset))
     {
     }
 
     friend bool operator==(const value_iterator & l, const value_iterator & r) { return l.view_ == r.view_; }
     friend bool operator!=(const value_iterator & l, const value_iterator & r) { return l.view_ != r.view_; }
 
   private:
     string_view_type view_;
 };
 
 /// A view type for a key of an environment
 struct key_view
 {
     using value_type       = char_type;
     using traits_type      = key_char_traits<char_type>;
     using string_view_type = basic_string_view<char_type, traits_type>;
     using string_type      = std::basic_string<char_type, key_char_traits<char_type>>;
 
     key_view() noexcept = default;
     key_view( const key_view& p ) = default;
     key_view( key_view&& p ) noexcept = default;
     template<typename Source, 
              typename = typename std::enable_if<is_constructible<string_view_type, Source>::value>::type>
     key_view( const Source& source ) : value_(source) {}
     key_view( const char_type * p) : value_(p) {}
     key_view(       char_type * p) : value_(p) {}
 
     ~key_view() = default;
 
     key_view& operator=( const key_view& p ) = default;
     key_view& operator=( key_view&& p ) noexcept = default;
     key_view& operator=( string_view_type source )
     {
         value_ = source;
         return *this;
     }
 
     void swap( key_view& other ) noexcept
     {
         std::swap(value_, other.value_);
     }
 
     string_view_type native() const noexcept {return value_;}
 
     operator string_view_type() const {return native();}
 
     int compare( const key_view& p ) const noexcept {return value_.compare(p.value_);}
     int compare( string_view_type str ) const {return value_.compare(str);}
     int compare( const value_type* s ) const {return value_.compare(s);}
 
     template< class CharT, class Traits = std::char_traits<CharT>,
             class Alloc = std::allocator<CharT> >
     std::basic_string<CharT,Traits,Alloc>
     basic_string( const Alloc& alloc = Alloc()) const
     {
         return BOOST_PROCESS_V2_NAMESPACE::detail::conv_string<CharT, Traits>(
             value_.data(), value_.size(), alloc);
     }
 
     std::string       string() const {return basic_string<char>();}
     std::wstring     wstring() const {return basic_string<wchar_t>();}
 
     string_type native_string() const
     {
         return basic_string<char_type, key_char_traits<char_type>>();
     }
 
     friend bool operator==(key_view l, key_view r) { return l.value_ == r.value_; }
     friend bool operator!=(key_view l, key_view r) { return l.value_ != r.value_; }
     friend bool operator<=(key_view l, key_view r) { return l.value_ <= r.value_; }
     friend bool operator>=(key_view l, key_view r) { return l.value_ >= r.value_; }
     friend bool operator< (key_view l, key_view r) { return l.value_ <  r.value_; }
     friend bool operator> (key_view l, key_view r) { return l.value_ >  r.value_; }
 
     bool empty() const {return value_.empty(); }
 
     template< class CharT, class Traits >
     friend std::basic_ostream<CharT,Traits>&
     operator<<( std::basic_ostream<CharT,Traits>& os, const key_view& p )
     {
         os << BOOST_PROCESS_V2_NAMESPACE::quoted(p.basic_string<CharT,Traits>());
         return os;
     }
 
     template< class CharT, class Traits >
     friend std::basic_istream<CharT,Traits>&
     operator>>( std::basic_istream<CharT,Traits>& is, key_view& p )
     {
         std::basic_string<CharT, Traits> t;
         is >> BOOST_PROCESS_V2_NAMESPACE::quoted(t);
         p = t;
         return is;
     }
     const value_type * data() const {return value_.data(); }
     std::size_t size() const {return value_.size(); }
   private:
     string_view_type value_;
 };
 
 /// A view for a value in an environment
 struct value_view
 {
     using value_type       = char_type;
     using string_view_type = basic_cstring_ref<char_type, value_char_traits<char_type>>;
     using string_type      = std::basic_string<char_type, value_char_traits<char_type>>;
     using traits_type      = value_char_traits<char_type>;
 
     value_view() noexcept = default;
     value_view( const value_view& p ) = default;
     value_view( value_view&& p ) noexcept = default;
     template<typename Source, typename = typename std::enable_if<is_constructible<string_view_type, Source>::value>::type>
     value_view( const Source& source ) : value_(source) {}
     value_view( const char_type * p) : value_(p) {}
     value_view(       char_type * p) : value_(p) {}
 
     ~value_view() = default;
 
     value_view& operator=( const value_view& p ) = default;
     value_view& operator=( value_view&& p ) noexcept = default;
     value_view& operator=( string_view_type source )
     {
         value_ = source;
         return *this;
     }
 
     void swap( value_view& other ) noexcept
     {
         std::swap(value_, other.value_);
     }
 
     string_view_type native() const noexcept {return value_;}
 
     operator string_view_type() const {return native();}
     operator typename string_view_type::string_view_type() const {return value_; }
 
     int compare( const value_view& p ) const noexcept {return value_.compare(p.value_);}
     int compare( string_view_type str ) const {return value_.compare(str);}
     int compare( const value_type* s ) const {return value_.compare(s);}
 
     template< class CharT, class Traits = std::char_traits<CharT>,
             class Alloc = std::allocator<CharT> >
     std::basic_string<CharT,Traits,Alloc>
     basic_string( const Alloc& alloc = Alloc() ) const
     {
         return BOOST_PROCESS_V2_NAMESPACE::detail::conv_string<CharT, Traits>(
                 value_.data(), value_.size(),  alloc);
     }
 
     std::string string() const       {return basic_string<char>();}
     std::wstring wstring() const     {return basic_string<wchar_t>();}
 
     string_type native_string() const
     {
         return basic_string<char_type, value_char_traits<char_type>>();
     }
 
     bool empty() const {return value_.empty(); }
 
     friend bool operator==(value_view l, value_view r) { return l.value_ == r.value_; }
     friend bool operator!=(value_view l, value_view r) { return l.value_ != r.value_; }
     friend bool operator<=(value_view l, value_view r) { return l.value_ <= r.value_; }
     friend bool operator>=(value_view l, value_view r) { return l.value_ >= r.value_; }
     friend bool operator< (value_view l, value_view r) { return l.value_ <  r.value_; }
     friend bool operator> (value_view l, value_view r) { return l.value_ >  r.value_; }
 
 
     template< class CharT, class Traits >
     friend std::basic_ostream<CharT,Traits>&
     operator<<( std::basic_ostream<CharT,Traits>& os, const value_view& p )
     {
         os << BOOST_PROCESS_V2_NAMESPACE::quoted(p.basic_string<CharT,Traits>());
         return os;
     }
 
     template< class CharT, class Traits >
     friend std::basic_istream<CharT,Traits>&
     operator>>( std::basic_istream<CharT,Traits>& is, value_view& p )
     {
         std::basic_string<CharT, Traits> t;
         is >> BOOST_PROCESS_V2_NAMESPACE::quoted(t);
         p = t;
         return is;
     }
     value_iterator begin() const {return value_iterator(value_.data());}
     value_iterator   end() const {return value_iterator(value_.data() , value_.size());}
 
     const char_type * c_str() {return value_.c_str(); }
     const value_type * data() const {return value_.data(); }
     std::size_t size() const {return value_.size(); }
 
   private:
     string_view_type value_;
 };
 
 /// A view for a key value pair in an environment
 struct key_value_pair_view
 {
   using value_type       = char_type;
   using string_type      = std::basic_string<char_type>;
   using string_view_type = basic_cstring_ref<char_type>;
   using traits_type      = std::char_traits<char_type>;
 
   key_value_pair_view() noexcept = default;
   key_value_pair_view( const key_value_pair_view& p ) = default;
   key_value_pair_view( key_value_pair_view&& p ) noexcept = default;
   template<typename Source,
            typename = typename std::enable_if<is_constructible<string_view_type, Source>::value>::type>
   key_value_pair_view( const Source& source ) : value_(source) {}
 
   key_value_pair_view( const char_type * p) : value_(p) {}
   key_value_pair_view(       char_type * p) : value_(p) {}
 
 
   ~key_value_pair_view() = default;
 
   key_value_pair_view& operator=( const key_value_pair_view& p ) = default;
   key_value_pair_view& operator=( key_value_pair_view&& p ) noexcept = default;
 
   void swap( key_value_pair_view& other ) noexcept
   {
       std::swap(value_, other.value_);
   }
 
   string_view_type native() const noexcept {return value_;}
 
   operator string_view_type() const {return native();}
   operator typename string_view_type::string_view_type() const {return value_; }
 
   int compare( key_value_pair_view p ) const noexcept 
   {
       const auto c = key().compare(p.key());
       if (c != 0)
             return c;
       return value().compare(p.value());
   }
   int compare( const string_type& str ) const
   {
       return compare(key_value_pair_view(str));
   }
   int compare( string_view_type str ) const 
   {
       string_type st(str.data(), str.size());
       return compare(st);
   }
   int compare( const value_type* s ) const
   {
       return compare(key_value_pair_view(s));
   }
 
   template< class CharT, class Traits = std::char_traits<CharT>, class Alloc = std::allocator<CharT> >
   std::basic_string<CharT,Traits,Alloc>
   basic_string( const Alloc& alloc = Alloc()) const
   {
       return BOOST_PROCESS_V2_NAMESPACE::detail::conv_string<CharT, Traits>(value_.begin(), value_.size(), alloc);
   }
 
   std::string string() const       {return basic_string<char>();}
   std::wstring wstring() const     {return basic_string<wchar_t>();}
 
   string_type native_string() const
   {
     return basic_string<char_type>();
   }
 
   bool empty() const {return value_.empty(); }
 
   key_view key() const
   {
       auto eq = value_.find(equality_sign);
       if (eq == 0)
       {
           auto eq2 = value_.find(equality_sign, 1);
           if (eq2 != string_type::npos)
               eq = eq2;
       }
       const auto res = native().substr(0,  eq == string_view_type::npos ? value_.size() : eq);
       return key_view::string_view_type(res.data(), res.size());
   }
   value_view value() const
   {
       auto eq = value_.find(equality_sign);
       if (eq == 0)
       {
           auto eq2 = value_.find(equality_sign, 1);
           if (eq2 != string_type::npos)
               eq = eq2;
       }
       return environment::value_view(native().substr(eq + 1));
   }
 
   friend bool operator==(key_value_pair_view l, key_value_pair_view r) { return l.compare(r) == 0; }
   friend bool operator!=(key_value_pair_view l, key_value_pair_view r) { return l.compare(r) != 0; }
   friend bool operator<=(key_value_pair_view l, key_value_pair_view r) { return l.compare(r) <= 0; }
   friend bool operator>=(key_value_pair_view l, key_value_pair_view r) { return l.compare(r) >= 0; }
   friend bool operator< (key_value_pair_view l, key_value_pair_view r) { return l.compare(r) <  0; }
   friend bool operator> (key_value_pair_view l, key_value_pair_view r) { return l.compare(r) >  0; }
 
 
   template< class CharT, class Traits >
   friend std::basic_ostream<CharT,Traits>&
   operator<<( std::basic_ostream<CharT,Traits>& os, const key_value_pair_view& p )
   {
       os << BOOST_PROCESS_V2_NAMESPACE::quoted(p.basic_string<CharT,Traits>());
       return os;
   }
 
   template< class CharT, class Traits >
   friend std::basic_istream<CharT,Traits>&
   operator>>( std::basic_istream<CharT,Traits>& is, key_value_pair_view& p )
   {
       std::basic_string<CharT, Traits> t;
       is >> BOOST_PROCESS_V2_NAMESPACE::quoted(t);
       p = t;
       return is;
   }
 
   template<std::size_t Idx>
   inline auto get() const -> typename conditional<Idx == 0u, BOOST_PROCESS_V2_NAMESPACE::environment::key_view,
                                                              BOOST_PROCESS_V2_NAMESPACE::environment::value_view>::type;
   const value_type * c_str() const noexcept
   {
     return value_.data();
   }
   const value_type * data() const {return value_.data(); }
   std::size_t size() const {return value_.size(); }
 
  private:
 
   string_view_type value_;
 };
 
 template<>
 inline key_view key_value_pair_view::get<0u>() const
 {
     return key();
 }
 
 template<>
 inline value_view key_value_pair_view::get<1u>() const
 {
     return value();
 }
 
 namespace detail
 {
 
 template<typename Char>
 std::size_t hash_step(std::size_t prev, Char c, std::char_traits<Char>)
 {
     return prev ^ (c << 1);
 }
 
 }
 
 inline std::size_t hash_value(const key_view & value)
 {
     std::size_t hash = 0u;
     for (auto c = value.data(); *c != *v2::detail::null_char_(*c); c++)
         hash = detail::hash_step(hash, *c, key_view::traits_type{});
     return hash ;
 }
 
 
 inline std::size_t hash_value(const BOOST_PROCESS_V2_NAMESPACE::environment::value_view & value)
 {
     std::size_t hash = 0u;
     for (auto c = value.data(); *c != *v2::detail::null_char_(*c); c++)
         hash = detail::hash_step(hash, *c, value_view::traits_type{});
     return hash ;
 }
 
 
 inline std::size_t hash_value(const BOOST_PROCESS_V2_NAMESPACE::environment::key_value_pair_view & value)
 {
     std::size_t hash = 0u;
     for (auto c = value.data(); *c != *v2::detail::null_char_(*c); c++)
         hash = detail::hash_step(hash, *c, key_value_pair_view::traits_type{});
     return hash ;
 }
 
 /// A class representing a key within an environment.
 struct key
 {
     using value_type       = char_type;
     using traits_type      = key_char_traits<char_type>;
     using string_type      = std::basic_string<char_type, traits_type>;
     using string_view_type = basic_string_view<char_type, traits_type>;
 
     key() {}
     key( const key& p ) = default;
     key( key&& p ) noexcept = default;
     key( const string_type& source ) : value_(source) {}
     key( string_type&& source ) : value_(std::move(source)) {}
     key( const value_type * raw ) : value_(raw) {}
     key(       value_type * raw ) : value_(raw) {}
 
     explicit key(key_view kv) : value_(kv.native_string()) {}
 
 
     template< class Source >
     key( const Source& source,
         decltype(std::declval<Source>().data()) = nullptr,
         decltype(std::declval<Source>().size()) = 0u)
         : value_(
              BOOST_PROCESS_V2_NAMESPACE::detail::conv_string<char_type, traits_type>(
                 source.data(), source.size()))
     {
     }
 
     key(const typename conditional<is_same<value_type, char>::value, wchar_t, char>::type  * raw)
         : value_(BOOST_PROCESS_V2_NAMESPACE::detail::conv_string<char_type, traits_type>(
                 raw, std::char_traits<std::decay<std::remove_pointer<decltype(raw)>::type>::type>::length(raw)))
     {
     }
 
     template< class InputIt >
     key( InputIt first, InputIt last)
         : key(std::basic_string<typename std::iterator_traits<typename std::decay<InputIt>::type>::value_type>(first, last))
     {
     }
 
     ~key() = default;
 
     key& operator=( const key& p ) = default;
     key& operator=( key&& p )
     {
       value_ = std::move(p.value_);
       return *this;
     }
     key& operator=( string_type&& source )
     {
         value_ = std::move(source);
         return *this;
     }
     template< class Source >
     key& operator=( const Source& source )
     {
         value_ = BOOST_PROCESS_V2_NAMESPACE::detail::conv_string<char_type, traits_type>(source.data(), source.size());
         return *this;
     }
 
     key& assign( string_type&& source )
     {
         value_ = std::move(source);
         return *this;
     }
     template< class Source >
     key& assign( const Source& source )
     {
         value_ = BOOST_PROCESS_V2_NAMESPACE::detail::conv_string<char_type, traits_type>(source.data(), source.size());
         return *this;
     }
 
     template< class InputIt >
     key& assign( InputIt first, InputIt last )
     {
 
         return assign(std::basic_string<typename std::iterator_traits<typename std::decay<InputIt>::type>::value_type>(first, last));
     }
 
     void clear() {value_.clear();}
 
     void swap( key& other ) noexcept
     {
         std::swap(value_, other.value_);
     }
 
     const value_type* c_str() const noexcept {return value_.c_str();}
     const string_type& native() const noexcept {return value_;}
     string_view_type native_view() const noexcept {return value_;}
 
     operator string_type() const {return native();}
     operator string_view_type() const {return native_view();}
 
     int compare( const key& p ) const noexcept {return value_.compare(p.value_);}
     int compare( const string_type& str ) const {return value_.compare(str);}
     int compare( string_view_type str ) const {return -str.compare(value_);}
     int compare( const value_type* s ) const {return value_.compare(s);}
 
     template< class CharT, class Traits = std::char_traits<CharT>,
         class Alloc = std::allocator<CharT> >
     std::basic_string<CharT,Traits,Alloc>
     basic_string( const Alloc& alloc = Alloc()) const
     {
         return BOOST_PROCESS_V2_NAMESPACE::detail::conv_string<CharT, Traits>(
             value_.data(), value_.size(), alloc);
     }
 
 
     std::string string() const       {return basic_string<char>();}
     std::wstring wstring() const     {return basic_string<wchar_t>();}
 
     const string_type & native_string() const
     {
         return value_;
     }
 
     bool empty() const {return value_.empty(); }
 
     friend bool operator==(const key & l, const key & r) { return l.value_ == r.value_; }
     friend bool operator!=(const key & l, const key & r) { return l.value_ != r.value_; }
     friend bool operator<=(const key & l, const key & r) { return l.value_ <= r.value_; }
     friend bool operator>=(const key & l, const key & r) { return l.value_ >= r.value_; }
     friend bool operator< (const key & l, const key & r) { return l.value_ <  r.value_; }
     friend bool operator> (const key & l, const key & r) { return l.value_ >  r.value_; }
 
     template< class CharT, class Traits >
     friend std::basic_ostream<CharT,Traits>&
     operator<<( std::basic_ostream<CharT,Traits>& os, const key& p )
     {
         os << BOOST_PROCESS_V2_NAMESPACE::quoted(p.basic_string<CharT,Traits>());
         return os;
     }
 
     template< class CharT, class Traits >
     friend std::basic_istream<CharT,Traits>&
     operator>>( std::basic_istream<CharT,Traits>& is, key& p )
     {
         std::basic_string<CharT, Traits> t;
         is >> BOOST_PROCESS_V2_NAMESPACE::quoted(t);
         p = t;
         return is;
     }
     const value_type * data() const {return value_.data(); }
     std::size_t size() const {return value_.size(); }
 
   private:
     string_type value_;
 };
 
 #if !defined(GENERATING_DOCUMENTATION)
 
 template<typename T, typename U>
 typename std::enable_if<
         ((std::is_same<T, key>::value || std::is_same<T, key_view>::value) &&
          std::is_convertible<const U &, key_view>::value)
         ||
         ((std::is_same<U, key>::value || std::is_same<U, key_view>::value) &&
          std::is_convertible<const T & , key_view>::value),
         bool>::type
 operator==(const T  &l, const U & r) { return key_view(l) == key_view(r); }
 
 template<typename T, typename U>
 typename std::enable_if<
         ((std::is_same<T, key>::value || std::is_same<T, key_view>::value) &&
          std::is_convertible<const U &, key_view>::value)
         ||
         ((std::is_same<U, key>::value || std::is_same<U, key_view>::value) &&
          std::is_convertible<const T & , key_view>::value),
         bool>::type
 operator!=(const T  &l, const U & r) { return key_view(l) != key_view(r); }
 
 template<typename T, typename U>
 typename std::enable_if<
         ((std::is_same<T, key>::value || std::is_same<T, key_view>::value) &&
          std::is_convertible<const U &, key_view>::value)
         ||
         ((std::is_same<U, key>::value || std::is_same<U, key_view>::value) &&
          std::is_convertible<const T & , key_view>::value),
         bool>::type
 operator<=(const T  &l, const U & r) { return key_view(l) <= key_view(r); }
 
 template<typename T, typename U>
 typename std::enable_if<
         ((std::is_same<T, key>::value || std::is_same<T, key_view>::value) &&
          std::is_convertible<const U &, key_view>::value)
         ||
         ((std::is_same<U, key>::value || std::is_same<U, key_view>::value) &&
          std::is_convertible<const T & , key_view>::value),
         bool>::type
 operator <(const T  &l, const U & r) { return key_view(l)  < key_view(r); }
 
 template<typename T, typename U>
 typename std::enable_if<
         ((std::is_same<T, key>::value || std::is_same<T, key_view>::value) &&
          std::is_convertible<const U &, key_view>::value)
         ||
         ((std::is_same<U, key>::value || std::is_same<U, key_view>::value) &&
          std::is_convertible<const T & , key_view>::value),
         bool>::type
 operator>=(const T  &l, const U & r) { return key_view(l) >= key_view(r); }
 
 template<typename T, typename U>
 typename std::enable_if<
         ((std::is_same<T, key>::value || std::is_same<T, key_view>::value) &&
          std::is_convertible<const U &, key_view>::value)
         ||
         ((std::is_same<U, key>::value || std::is_same<U, key_view>::value) &&
          std::is_convertible<const T & , key_view>::value),
         bool>::type
 operator >(const T  &l, const U & r) { return key_view(l) >  key_view(r); }
 
 #else
 
 
 bool operator==(const value_view &, const value_view);
 bool operator!=(const value_view &, const value_view);
 bool operator<=(const value_view &, const value_view);
 bool operator< (const value_view &, const value_view);
 bool operator> (const value_view &, const value_view);
 bool operator>=(const value_view &, const value_view);
 
 #endif
 
 
 struct value
 {
     using value_type       = char_type;
     using traits_type      = value_char_traits<char_type>;
     using string_type      = std::basic_string<char_type, traits_type>;
     using string_view_type = basic_cstring_ref<char_type, traits_type>;
 
     value() {}
     value( const value& p ) = default;
 
     value( const string_type& source ) : value_(source) {}
     value( string_type&& source ) : value_(std::move(source)) {}
     value( const value_type * raw ) : value_(raw) {}
     value(       value_type * raw ) : value_(raw) {}
 
     explicit value(value_view kv) : value_(kv.c_str()) {}
 
     template< class Source >
     value( const Source& source,
            decltype(std::declval<Source>().data()) = nullptr,
     decltype(std::declval<Source>().size()) = 0u)
     : value_(BOOST_PROCESS_V2_NAMESPACE::detail::conv_string<char_type, traits_type>(
         source.data(), source.size()))
     {
     }
 
     value(const typename conditional<is_same<value_type, char>::value, wchar_t, char>::type  * raw)
             : value_(BOOST_PROCESS_V2_NAMESPACE::detail::conv_string<char_type, traits_type>(
             raw, std::char_traits<std::decay<std::remove_pointer<decltype(raw)>::type>::type>::length(raw)))
     {
     }
 
     template< class InputIt >
     value( InputIt first, InputIt last)
             : value(std::basic_string<typename std::iterator_traits<typename std::decay<InputIt>::type>::value_type>(first, last))
     {
     }
 
     ~value() = default;
 
     value& operator=( const value& p ) = default;
     value& operator=( value&& p )
     {
       value_ = std::move(p.value_);
       return *this;
     }
     value& operator=( string_type&& source )
     {
         value_ = std::move(source);
         return *this;
     }
     template< class Source >
     value& operator=( const Source& source )
     {
         value_ = BOOST_PROCESS_V2_NAMESPACE::detail::conv_string<char_type, traits_type>(
             source.data(), source.size);
         return *this;
     }
 
     value& assign( string_type&& source )
     {
         value_ = std::move(source);
         return *this;
     }
     template< class Source >
     value& assign( const Source& source )
     {
       value_ = BOOST_PROCESS_V2_NAMESPACE::detail::conv_string<char_type, traits_type>(
           source.data(), source.size());
       return *this;
     }
 
     template< class InputIt >
     value& assign( InputIt first, InputIt last )
     {
         return assign(std::basic_string<typename std::iterator_traits<typename std::decay<InputIt>::type>::value_type>(first, last));
     }
 
     void push_back(const value & sv)
     {
         (value_ += delimiter) += sv;
     }
 
     void clear() {value_.clear();}
 
     void swap( value& other ) noexcept
     {
         std::swap(value_, other.value_);
     }
 
     const value_type* c_str() const noexcept {return value_.c_str();}
     const string_type& native() const noexcept {return value_;}
     string_view_type native_view() const noexcept {return value_;}
 
     operator string_type() const {return native();}
     operator string_view_type() const {return native_view();}
     operator typename string_view_type::string_view_type() const {return value_; }
 
     int compare( const value& p ) const noexcept {return value_.compare(p.value_);}
     int compare( const string_type& str ) const {return value_.compare(str);}
     int compare( string_view_type str ) const {return -str.compare(value_);}
     int compare( const value_type* s ) const {return value_.compare(s);}
 
     template< class CharT, class Traits = std::char_traits<CharT>,
             class Alloc = std::allocator<CharT> >
     std::basic_string<CharT,Traits,Alloc>
     basic_string( const Alloc& alloc = Alloc()) const
     {
         return BOOST_PROCESS_V2_NAMESPACE::detail::conv_string<CharT, Traits>(
             value_.data(), value_.size(),alloc);
     }
 
     std::string string() const       {return basic_string<char>();}
     std::wstring wstring() const     {return basic_string<wchar_t>();}
 
 
     const string_type & native_string() const
     {
         return value_;
     }
 
     bool empty() const {return value_.empty(); }
 
     friend bool operator==(const value & l, const value & r) { return l.value_ == r.value_; }
     friend bool operator!=(const value & l, const value & r) { return l.value_ != r.value_; }
     friend bool operator<=(const value & l, const value & r) { return l.value_ <= r.value_; }
     friend bool operator>=(const value & l, const value & r) { return l.value_ >= r.value_; }
     friend bool operator< (const value & l, const value & r) { return l.value_ <  r.value_; }
     friend bool operator> (const value & l, const value & r) { return l.value_ >  r.value_; }
 
     template< class CharT, class Traits >
     friend std::basic_ostream<CharT,Traits>&
     operator<<( std::basic_ostream<CharT,Traits>& os, const value& p )
     {
         os << BOOST_PROCESS_V2_NAMESPACE::quoted(p.basic_string<CharT,Traits>());
         return os;
     }
 
     template< class CharT, class Traits >
     friend std::basic_istream<CharT,Traits>&
     operator>>( std::basic_istream<CharT,Traits>& is, value& p )
     {
         std::basic_string<CharT, Traits> t;
         is >> BOOST_PROCESS_V2_NAMESPACE::quoted(t);
         p = t;
         return is;
     }
 
     value_iterator begin() const {return value_iterator(value_.data());}
     value_iterator   end() const {return value_iterator(value_.data(), value_.size());}
     const value_type * data() const {return value_.data(); }
     std::size_t size() const {return value_.size(); }
 
   private:
     string_type value_;
 };
 
 
 #if !defined(GENERATING_DOCUMENTATION)
 
 template<typename T, typename U>
 typename std::enable_if<
         ((std::is_same<T, value>::value || std::is_same<T, value_view>::value) &&
          std::is_convertible<const U &, value_view>::value)
         ||
         ((std::is_same<U, value>::value || std::is_same<U, value_view>::value) &&
          std::is_convertible<const T & , value_view>::value),
         bool>::type
 operator==(const T  &l, const U & r) { return value_view(l) == value_view(r); }
 
 template<typename T, typename U>
 typename std::enable_if<
         ((std::is_same<T, value>::value || std::is_same<T, value_view>::value) &&
          std::is_convertible<const U &, value_view>::value)
         ||
         ((std::is_same<U, value>::value || std::is_same<U, value_view>::value) &&
          std::is_convertible<const T & , value_view>::value),
         bool>::type
 operator!=(const T  &l, const U & r) { return value_view(l) != value_view(r); }
 
 template<typename T, typename U>
 typename std::enable_if<
         ((std::is_same<T, value>::value || std::is_same<T, value_view>::value) &&
          std::is_convertible<const U &, value_view>::value)
         ||
         ((std::is_same<U, value>::value || std::is_same<U, value_view>::value) &&
          std::is_convertible<const T & , value_view>::value),
         bool>::type
 operator<=(const T  &l, const U & r) { return value_view(l) <= value_view(r); }
 
 template<typename T, typename U>
 typename std::enable_if<
         ((std::is_same<T, value>::value || std::is_same<T, value_view>::value) &&
          std::is_convertible<const U &, value_view>::value)
         ||
         ((std::is_same<U, value>::value || std::is_same<U, value_view>::value) &&
          std::is_convertible<const T & , value_view>::value),
         bool>::type
 operator <(const T  &l, const U & r) { return value_view(l)  < value_view(r); }
 
 template<typename T, typename U>
 typename std::enable_if<
         ((std::is_same<T, value>::value || std::is_same<T, value_view>::value) &&
          std::is_convertible<const U &, value_view>::value)
         ||
         ((std::is_same<U, value>::value || std::is_same<U, value_view>::value) &&
          std::is_convertible<const T & , value_view>::value),
         bool>::type
 operator>=(const T  &l, const U & r) { return value_view(l) >= value_view(r); }
 
 template<typename T, typename U>
 typename std::enable_if<
         ((std::is_same<T, value>::value || std::is_same<T, value_view>::value) &&
          std::is_convertible<const U &, value_view>::value)
         ||
         ((std::is_same<U, value>::value || std::is_same<U, value_view>::value) &&
          std::is_convertible<const T & , value_view>::value),
         bool>::type
 operator >(const T  &l, const U & r) { return value_view(l) >  value_view(r); }
 
 #else
 
 bool operator==(const value_view &, const value_view);
 bool operator!=(const value_view &, const value_view);
 bool operator<=(const value_view &, const value_view);
 bool operator< (const value_view &, const value_view);
 bool operator> (const value_view &, const value_view);
 bool operator>=(const value_view &, const value_view);
 
 #endif
 
 struct key_value_pair
 {
     using value_type       = char_type;
     using traits_type      = std::char_traits<char_type>;
     using string_type      = std::basic_string<char_type>;
     using string_view_type = basic_cstring_ref<char_type>;
 
     key_value_pair() {}
     key_value_pair( const key_value_pair& p ) = default;
     key_value_pair( key_value_pair&& p ) noexcept = default;
     key_value_pair(key_view key, value_view value) : value_(key.basic_string<char_type, traits_type>() + equality_sign + 
                                                             value.basic_string<char_type, traits_type>()) {}
 
     key_value_pair(key_view key, std::initializer_list<basic_string_view<char_type>> values)
     {
         const auto sz = std::accumulate(values.begin(), values.end(),
                                         key.size(), [](std::size_t sz, const basic_string_view<char_type> & str) { return sz + str.size() + 1;});
 
         value_.reserve(sz);
         value_.append(key.data(), key.size());
         value_ += equality_sign;
         for (auto & value : values)
         {
             if (value_.back() != equality_sign)
                 value_ += delimiter;
             value_.append(value.data(), value.size());
         }
     }
 
     key_value_pair( const string_type& source ) : value_(source) {}
     key_value_pair( string_type&& source ) : value_(std::move(source)) {}
     key_value_pair( const value_type * raw ) : value_(raw) {}
     key_value_pair(       value_type * raw ) : value_(raw) {}
 
     explicit key_value_pair(key_value_pair_view kv) : value_(kv.c_str()) {}
 
     template< class Source >
     key_value_pair( const Source& source,
            decltype(std::declval<Source>().data()) = nullptr,
            decltype(std::declval<Source>().size()) = 0u)
             : value_(BOOST_PROCESS_V2_NAMESPACE::detail::conv_string<char_type, traits_type>(
                 source.data(), source.size()))
     {
     }
 
     template< typename Key, 
               typename Value >
     key_value_pair(
          const std::pair<Key, Value> & kv/*,
          typename std::enable_if<std::is_constructible<struct key,   Key >::value && 
                                  std::is_constructible<struct value, Value>::value
                 >::type = 0*/) : value_(((struct key)(kv.first)).basic_string<char_type, traits_type>() + equality_sign 
                                       + ((struct value)(kv.second)).basic_string<char_type, traits_type>())
     {}
 
     key_value_pair(const typename conditional<is_same<value_type, char>::value, wchar_t, char>::type  * raw)
             : value_(BOOST_PROCESS_V2_NAMESPACE::detail::conv_string<char_type, traits_type>(
                      raw,
                      std::char_traits<std::decay<std::remove_pointer<decltype(raw)>::type>::type>::length(raw)))
     {
     }
 
     template< class InputIt , typename std::iterator_traits<InputIt>::iterator_category>
     key_value_pair( InputIt first, InputIt last )
             : key_value_pair(std::basic_string<typename std::iterator_traits<typename std::decay<InputIt>::type>::value_type>(first, last))
     {
     }
 
     ~key_value_pair() = default;
 
     key_value_pair& operator=( const key_value_pair& p ) = default;
     key_value_pair& operator=( key_value_pair&& p )
     {
       value_ = std::move(p.value_);
       return *this;
     }
     key_value_pair& operator=( string_type&& source )
     {
         value_ = std::move(source);
         return *this;
     }
     template< class Source >
     key_value_pair& operator=( const Source& source )
     {
         value_ = BOOST_PROCESS_V2_NAMESPACE::detail::conv_string<char_type, traits_type>(
             source.data(), source.size());
         return *this;
     }
 
     key_value_pair& assign( string_type&& source )
     {
         value_ = std::move(source);
         return *this;
     }
     template< class Source >
     key_value_pair& assign( const Source& source )
     {
         value_ = BOOST_PROCESS_V2_NAMESPACE::detail::conv_string<char_type, traits_type>(
             source.data(), source.size());
         return *this;
     }
 
 
     template< class InputIt >
     key_value_pair& assign( InputIt first, InputIt last )
     {
         return assign(std::basic_string<typename std::iterator_traits<typename std::decay<InputIt>::type>::value_type>(first, last));
     }
 
     void clear() {value_.clear();}
 
     void swap( key_value_pair& other ) noexcept
     {
         std::swap(value_, other.value_);
     }
 
     const value_type* c_str() const noexcept {return value_.c_str();}
     const string_type& native() const noexcept {return value_;}
     string_view_type native_view() const noexcept {return value_;}
 
     operator string_type() const {return native();}
     operator string_view_type() const {return native_view();}
     operator typename string_view_type::string_view_type() const {return native_view();}
     operator key_value_pair_view() const {return native_view();}
 
     int compare( const key_value_pair& p ) const noexcept 
     {
         return key_value_pair_view(*this).compare(key_value_pair_view(p));
     }
     
     int compare( const string_type& str ) const 
     {
         return key_value_pair_view(*this).compare(str);
     }
     int compare( string_view_type str ) const   
     {
         return key_value_pair_view(*this).compare(str);
     }
     int compare( const value_type* s ) const
     {
         return key_value_pair_view(*this).compare(s);
     }
 
     template< class CharT, class Traits = std::char_traits<CharT>, class Alloc = std::allocator<CharT> >
     std::basic_string<CharT,Traits,Alloc>
     basic_string( const Alloc& alloc = Alloc() ) const
     {
         return BOOST_PROCESS_V2_NAMESPACE::detail::conv_string<CharT, Traits>(value_.data(), value_.size(), alloc);
     }
 
     std::string string() const       {return basic_string<char>();}
     std::wstring wstring() const     {return basic_string<wchar_t>();}
 
     const string_type & native_string() const
     {
         return value_;
     }
 
     friend bool operator==(const key_value_pair & l, const key_value_pair & r) { return l.compare(r) == 0; }
     friend bool operator!=(const key_value_pair & l, const key_value_pair & r) { return l.compare(r) != 0; }
     friend bool operator<=(const key_value_pair & l, const key_value_pair & r) { return l.compare(r) <= 0; }
     friend bool operator>=(const key_value_pair & l, const key_value_pair & r) { return l.compare(r) >= 0; }
     friend bool operator< (const key_value_pair & l, const key_value_pair & r) { return l.compare(r) <  0; }
     friend bool operator> (const key_value_pair & l, const key_value_pair & r) { return l.compare(r) >  0; }
 
     bool empty() const {return value_.empty(); }
 
     struct key_view key() const
     {
         auto eq = value_.find(equality_sign);
         if (eq == 0)
         {
             auto eq2 = value_.find(equality_sign, 1);
             if (eq2 != string_type::npos)
               eq = eq2;
         }
         const auto k = native_view().substr(0, eq);
 
         return BOOST_PROCESS_V2_NAMESPACE::environment::key_view::string_view_type (k.data(), k.size());
     }
     struct value_view value() const
     {
         auto eq = value_.find(equality_sign);
         if (eq == 0)
         {
             auto eq2 = value_.find(equality_sign, 1);
             if (eq2 != string_type::npos)
                eq = eq2;
         }
         return value_view::string_view_type(native_view().substr(eq + 1));
     }
 
     template< class CharT, class Traits >
     friend std::basic_ostream<CharT,Traits>&
     operator<<( std::basic_ostream<CharT,Traits>& os, const key_value_pair& p )
     {
         os << BOOST_PROCESS_V2_NAMESPACE::quoted(p.basic_string<CharT,Traits>());
         return os;
     }
 
     template< class CharT, class Traits >
     friend std::basic_istream<CharT,Traits>&
     operator>>( std::basic_istream<CharT,Traits>& is, key_value_pair& p )
     {
         is >> BOOST_PROCESS_V2_NAMESPACE::quoted(p.value_);
         return is;
     }
 
     const value_type * data() const {return value_.data(); }
     std::size_t size() const {return value_.size(); }
 
     template<std::size_t Idx>
     inline auto get() const 
             -> typename conditional<Idx == 0u, BOOST_PROCESS_V2_NAMESPACE::environment::key_view,
                                             BOOST_PROCESS_V2_NAMESPACE::environment::value_view>::type;
 
 private:
     string_type value_;
 };
 
 #if !defined(GENERATING_DOCUMENTATION)
 
 template<typename T, typename U>
 typename std::enable_if<
         ((std::is_same<T, key_value_pair>::value || std::is_same<T, key_value_pair_view>::value) &&
          std::is_convertible<const U &, key_value_pair_view>::value)
         ||
         ((std::is_same<U, key_value_pair>::value || std::is_same<U, key_value_pair_view>::value) &&
          std::is_convertible<const T & , key_value_pair_view>::value),
         bool>::type
 operator==(const T  &l, const U & r) { return key_value_pair_view(l) == key_value_pair_view(r); }
 
 template<typename T, typename U>
 typename std::enable_if<
         ((std::is_same<T, key_value_pair>::value || std::is_same<T, key_value_pair_view>::value) &&
          std::is_convertible<const U &, key_value_pair_view>::value)
         ||
         ((std::is_same<U, key_value_pair>::value || std::is_same<U, key_value_pair_view>::value) &&
          std::is_convertible<const T & , key_value_pair_view>::value),
         bool>::type
 operator!=(const T  &l, const U & r) { return key_value_pair_view(l) != key_value_pair_view(r); }
 
 template<typename T, typename U>
 typename std::enable_if<
         ((std::is_same<T, key_value_pair>::value || std::is_same<T, key_value_pair_view>::value) &&
          std::is_convertible<const U &, key_value_pair_view>::value)
         ||
         ((std::is_same<U, key_value_pair>::value || std::is_same<U, key_value_pair_view>::value) &&
          std::is_convertible<const T & , key_value_pair_view>::value),
         bool>::type
 operator<=(const T  &l, const U & r) { return key_value_pair_view(l) <= key_value_pair_view(r); }
 
 template<typename T, typename U>
 typename std::enable_if<
         ((std::is_same<T, key_value_pair>::value || std::is_same<T, key_value_pair_view>::value) &&
          std::is_convertible<const U &, key_value_pair_view>::value)
         ||
         ((std::is_same<U, key_value_pair>::value || std::is_same<U, key_value_pair_view>::value) &&
          std::is_convertible<const T & , key_value_pair_view>::value),
         bool>::type
 operator <(const T  &l, const U & r) { return key_value_pair_view(l)  < key_value_pair_view(r); }
 
 template<typename T, typename U>
 typename std::enable_if<
         ((std::is_same<T, key_value_pair>::value || std::is_same<T, key_value_pair_view>::value) &&
          std::is_convertible<const U &, key_value_pair_view>::value)
         ||
         ((std::is_same<U, key_value_pair>::value || std::is_same<U, key_value_pair_view>::value) &&
          std::is_convertible<const T & , key_value_pair_view>::value),
         bool>::type
 operator>=(const T  &l, const U & r) { return key_value_pair_view(l) >= key_value_pair_view(r); }
 
 template<typename T, typename U>
 typename std::enable_if<
         ((std::is_same<T, key_value_pair>::value || std::is_same<T, key_value_pair_view>::value) &&
          std::is_convertible<const U &, key_value_pair_view>::value)
         ||
         ((std::is_same<U, key_value_pair>::value || std::is_same<U, key_value_pair_view>::value) &&
          std::is_convertible<const T & , key_value_pair_view>::value),
         bool>::type
 operator >(const T  &l, const U & r) { return key_value_pair_view(l) >  key_value_pair_view(r); }
 
 #else
 
 bool operator==(const key_value_pair_view &, const key_value_pair_view);
 bool operator!=(const key_value_pair_view &, const key_value_pair_view);
 bool operator<=(const key_value_pair_view &, const key_value_pair_view);
 bool operator< (const key_value_pair_view &, const key_value_pair_view);
 bool operator> (const key_value_pair_view &, const key_value_pair_view);
 bool operator>=(const key_value_pair_view &, const key_value_pair_view);
 
 #endif
 
 
 template<>
 inline key_view key_value_pair::get<0u>() const
 {
     return key();
 }
 
 template<>
 inline value_view key_value_pair::get<1u>() const
 {
     return value();
 }
 
 }
 BOOST_PROCESS_V2_END_NAMESPACE
 
 namespace std
 {
 
 template<>
 class tuple_size<BOOST_PROCESS_V2_NAMESPACE::environment::key_value_pair> : integral_constant<std::size_t, 2u> {};
 
 template<>
 class tuple_element<0u, BOOST_PROCESS_V2_NAMESPACE::environment::key_value_pair> 
 {
   public: 
     using type = BOOST_PROCESS_V2_NAMESPACE::environment::key_view;
 };
 
 template<>
 class tuple_element<1u, BOOST_PROCESS_V2_NAMESPACE::environment::key_value_pair> 
 {
   public: 
     using type = BOOST_PROCESS_V2_NAMESPACE::environment::value_view;
 };
 
 template<std::size_t Idx>
 inline auto get(const BOOST_PROCESS_V2_NAMESPACE::environment::key_value_pair & kvp) 
         -> typename std::tuple_element<Idx, BOOST_PROCESS_V2_NAMESPACE::environment::key_value_pair>::type
 {
     return kvp.get<Idx>();
 }
 
 template<>
 class tuple_size<BOOST_PROCESS_V2_NAMESPACE::environment::key_value_pair_view> : integral_constant<std::size_t, 2u> {};
 
 template<>
 class tuple_element<0u, BOOST_PROCESS_V2_NAMESPACE::environment::key_value_pair_view>
 {
   public:
     using type = BOOST_PROCESS_V2_NAMESPACE::environment::key_view;
 };
 
 template<>
 class tuple_element<1u, BOOST_PROCESS_V2_NAMESPACE::environment::key_value_pair_view>
 {
   public:
     using type = BOOST_PROCESS_V2_NAMESPACE::environment::value_view;
 };
 
 template<std::size_t Idx>
 inline auto get(BOOST_PROCESS_V2_NAMESPACE::environment::key_value_pair_view kvp) 
         -> typename std::tuple_element<Idx, BOOST_PROCESS_V2_NAMESPACE::environment::key_value_pair_view>::type
 {
     return kvp.get<Idx>();
 }
 
 }
 
 BOOST_PROCESS_V2_BEGIN_NAMESPACE
 namespace environment 
 {
 
 
 /// A view object for the current environment of this process.
 /**
  * The view might (windows) or might not (posix) be owning;
  * if it owns it will deallocate the on destruction, like a unique_ptr.
  * 
  * Note that accessing the environment in this way is not thread-safe.
  * 
  * @code
  * 
  * void dump_my_env(current_view env = current())
  * {
  *    for (auto  & [k, v] : env)
  *        std::cout << k.string() << " = "  << v.string() << std::endl;
  * }
  * 
  * @endcode
  * 
  * 
  */ 
 struct current_view
 {
     using native_handle_type = environment::native_handle_type;
     using value_type = key_value_pair_view;
 
     current_view() = default;
     current_view(current_view && nt) = default;
 
     native_handle_type  native_handle() { return handle_.get(); }
 
     struct iterator
     {
         using value_type        = key_value_pair_view;
         using difference_type   = int;
         using reference         = key_value_pair_view;
         using pointer           = key_value_pair_view;
         using iterator_category = std::forward_iterator_tag;
 
         iterator() = default;
         iterator(const iterator & ) = default;
         iterator(const native_iterator &native_handle) : iterator_(native_handle) {}
 
         iterator & operator++()
         {
             iterator_ = detail::next(iterator_);
             return *this;
         }
 
         iterator operator++(int)
         {
             auto last = *this;
             iterator_ = detail::next(iterator_);
             return last;
         }
         key_value_pair_view operator*() const
         {
             return detail::dereference(iterator_);
         }
 
         friend bool operator==(const iterator & l, const iterator & r) {return l.iterator_ == r.iterator_;}
         friend bool operator!=(const iterator & l, const iterator & r) {return l.iterator_ != r.iterator_;}
 
       private:
         environment::native_iterator iterator_;
     };
 
     iterator begin() const {return iterator(handle_.get());}
     iterator   end() const {return iterator(detail::find_end(handle_.get()));}
 
  private:
 
   std::unique_ptr<typename remove_pointer<native_handle_type>::type,
                     detail::native_handle_deleter> handle_{environment::detail::load_native_handle()};
 };
 
 /// Obtain a handle to the current environment
 inline current_view current() {return current_view();}
 
 namespace detail
 {
 
 template<typename Environment>
 auto find_key(Environment & env, key_view ky) 
     -> typename std::enable_if<std::is_convertible<decltype(*std::begin(env)), key_value_pair_view>::value, value_view>::type
 {
     const auto itr = std::find_if(std::begin(env), std::end(env),
                                   [&](key_value_pair_view vp)
                                   {
                                     auto tmp = std::get<0>(vp) == ky;
                                     if (tmp)
                                       return true;
                                     else
                                       return false;
                                   });
     
     if (itr != std::end(env))
       return key_value_pair_view(*itr).value();
     else
       return {};
 }
 
 template<typename Environment>
 auto find_key(Environment & env, key_view ky) 
     -> typename std::enable_if<
     !std::is_convertible<decltype(*std::begin(env)), key_value_pair_view>::value && 
      std::is_convertible<decltype(*std::begin(env)), key_value_pair>::value, 
     value>::type
 {
     const auto itr = std::find_if(std::begin(env), std::end(env),
                                   [&](key_value_pair vp)
                                   {
                                     auto tmp = std::get<0>(vp) == ky;
                                     if (tmp)
                                       return true;
                                     else
                                       return false;
                                   });
     if (itr != std::end(env))
       return key_value_pair(*itr).value();
     else
       return {};
 }
 
 
 }
 
 
 /// Find the home folder in an environment-like type.
 /** 
  * @param env The environment to search. Defaults to the current environment of this process
  * 
  * The environment type passed in must be a range with value T that fulfills the following requirements:
  * 
  *  For `T value`
  *
  *  - std::get<0>(value) must return a type comparable to `key_view`.
  *  - std::get<1>(value) must return a type convertible to filesystem::path.
  * 
  * @return A filesystem::path to the home directory or an empty path if it cannot be found.
  * 
  */
 template<typename Environment = current_view>
 inline filesystem::path home(Environment && env = current())
 {
 #if defined(BOOST_PROCESS_V2_WINDOWS)
   return detail::find_key(env, L"HOMEDRIVE").native_string() 
        + detail::find_key(env, L"HOMEPATH").native_string();
 #else
   return detail::find_key(env, "HOME").native_string();
 #endif
 }
 
 /// Find the executable `name` in an environment-like type.
 /** 
  * @param env The environment to search. Defaults to the current environment of this process
  * 
  * The environment type passed in must be a range with value T that fulfills the following requirements:
  * 
  *  For `T value`
  *
  *  - std::get<0>(value) must return a type comparable to `key_view`.
  *  - std::get<1>(value) must return a type convertible to `value_view`.
  * 
  * 
  * @return A filesystem::path to the executable or an empty path if it cannot be found.
  * 
  */
 template<typename Environment = current_view>
 inline BOOST_PROCESS_V2_NAMESPACE::filesystem::path find_executable(
                                              BOOST_PROCESS_V2_NAMESPACE::filesystem::path name,
                                              Environment && env = current())
 {
 
 #if defined(BOOST_PROCESS_V2_WINDOWS)
     auto path = detail::find_key(env, L"PATH");
     auto pathext = detail::find_key(env, L"PATHEXT");
     for (auto pp_view : path)
     {
         // first check if it has the extension already
         BOOST_PROCESS_V2_NAMESPACE::filesystem::path full_nm(name);
         BOOST_PROCESS_V2_NAMESPACE::filesystem::path pp(pp_view.begin(), pp_view.end());
         auto p = pp / full_nm;
         error_code ec;
 
         if (detail::is_executable(p, ec) && !ec)
             return p;
 
         for (auto ext : pathext)
         {
             ec.clear();
             BOOST_PROCESS_V2_NAMESPACE::filesystem::path nm(name);
             nm.concat(ext.begin(), ext.end());
 
             auto p = pp / nm;
 
             if (detail::is_executable(p, ec) && !ec)
                 return p;
         }
     }
 #else
     for (auto pp_view : detail::find_key(env, "PATH"))
     {
         auto p = BOOST_PROCESS_V2_NAMESPACE::filesystem::path(pp_view.begin(), pp_view.end()) / name;
         error_code ec;
         bool is_exec = detail::is_executable(p, ec);
         if (!ec && is_exec)
             return p;
     }
 #endif
     return {};
 }
 
 /// Get an environment variable from the current process.
 inline value get(const key & k, error_code & ec) { return detail::get(k.c_str(), ec);}
 /// Throwing @overload value get(const key & k, error_code & ec)
 inline value get(const key & k)
 {
   error_code ec;
   auto tmp = detail::get(k.c_str(), ec);
   BOOST_PROCESS_V2_NAMESPACE::detail::throw_error(ec, "environment::get");
   return tmp;
 }
 
 /// Disambiguating @overload value get(const key & k, error_code & ec)
 inline value get(basic_cstring_ref<char_type, key_char_traits<char_type>> k, error_code & ec)
 {
   return detail::get(k, ec);
 }
 /// Disambiguating @overload value get(const key & k)
 inline value get(basic_cstring_ref<char_type, key_char_traits<char_type>> k)
 {
   error_code ec;
   auto tmp = detail::get(k, ec);
   BOOST_PROCESS_V2_NAMESPACE::detail::throw_error(ec, "environment::get");
   return tmp;
 }
 
 
 /// Disambiguating @overload value get(const key & k, error_code & ec)
 inline value get(const char_type * c, error_code & ec) { return detail::get(c, ec);}
 /// Disambiguating @overload value get(const key & k)
 inline value get(const char_type * c)
 {
   error_code ec;
   auto tmp = detail::get(c, ec);
   BOOST_PROCESS_V2_NAMESPACE::detail::throw_error(ec, "environment::get");
   return tmp;
 }
 
 /// Set an environment variable for the current process.
 inline void set(const key & k, value_view vw, error_code & ec) { detail::set(k, vw, ec);}
 /// Throwing @overload void set(const key & k, value_view vw, error_code & ec)
 inline void set(const key & k, value_view vw)
 {
   error_code ec;
   detail::set(k, vw, ec);
   BOOST_PROCESS_V2_NAMESPACE::detail::throw_error(ec, "environment::set");
 }
 
 /// Disambiguating @overload void set(const key & k, value_view vw, error_code & ec)
 inline void set(basic_cstring_ref<char_type, key_char_traits<char_type>> k, value_view vw, error_code & ec) { detail::set(k, vw, ec);}
 /// Disambiguating @overload void set(const key & k, value_view vw, error_code & ec)
 inline void set(basic_cstring_ref<char_type, key_char_traits<char_type>> k, value_view vw)
 {
   error_code ec;
   detail::set(k, vw, ec);
   BOOST_PROCESS_V2_NAMESPACE::detail::throw_error(ec, "environment::set");
 }
 
 
 /// Disambiguating @overload void set(const key & k, value_view vw, error_code & ec)
 inline void set(const char_type * k, value_view vw, error_code & ec) { detail::set(k, vw, ec);}
 /// Disambiguating @overload void set(const key & k, value_view vw, error_code & ec)
 inline void set(const char_type * k, value_view vw)
 {
   error_code ec;
   detail::set(k, vw, ec);
   BOOST_PROCESS_V2_NAMESPACE::detail::throw_error(ec, "environment::set");
 }
 
 /// Disambiguating @overload void set(const key & k, value_view vw, error_code & ec)
 template<typename Char, typename = typename std::enable_if<!std::is_same<Char, char_type>::value>::type>
 inline void set(const key & k, const Char * vw, error_code & ec)
 {
     value val{vw};
     detail::set(k, val, ec);
 }
 /// Disambiguating @overload void set(const key & k, value_view vw, error_code & ec)
 template<typename Char, typename = typename std::enable_if<!std::is_same<Char, char_type>::value>::type>
 inline void set(const key & k, const Char * vw)
 {
     error_code ec;
     value val{vw};
     detail::set(k, val, ec);
     BOOST_PROCESS_V2_NAMESPACE::detail::throw_error(ec, "environment::set");
 }
 
 /// Disambiguating @overload void set(const key & k, value_view vw, error_code & ec)
 template<typename Char, typename = typename std::enable_if<!std::is_same<Char, char_type>::value>::type>
 inline void set(basic_cstring_ref<char_type, key_char_traits<char_type>> k, const Char * vw, error_code & ec)
 {
     value val{vw};
     detail::set(k, val, ec);
 }
 
 /// Disambiguating @overload void set(const key & k, value_view vw, error_code & ec)
 template<typename Char, typename = typename std::enable_if<!std::is_same<Char, char_type>::value>::type>
 inline void set(basic_cstring_ref<char_type, key_char_traits<char_type>> k, const Char * vw)
 {
     error_code ec;
     value val{vw};
     detail::set(k, val, ec);
     BOOST_PROCESS_V2_NAMESPACE::detail::throw_error(ec, "environment::set");
 }
 
 /// Disambiguating @overload void set(const key & k, value_view vw, error_code & ec)
 template<typename Char, typename = typename std::enable_if<!std::is_same<Char, char_type>::value>::type>
 inline void set(const char_type * k, const Char * vw, error_code & ec)
 {
     value val{vw};
     detail::set(k, val, ec);
 }
 
 /// Disambiguating @overload void set(const key & k, value_view vw, error_code & ec)
 template<typename Char, typename = typename std::enable_if<!std::is_same<Char, char_type>::value>::type>
 inline void set(const char_type * k, const Char * vw)
 {
     error_code ec;
     value val{vw};
     detail::set(k, val, ec);
     BOOST_PROCESS_V2_NAMESPACE::detail::throw_error(ec, "environment::set");
 }
 
 
 /// Remove an environment variable from the current process.
 inline void unset(const key & k, error_code & ec) { detail::unset(k, ec);}
 /// Throwing @overload void unset(const key & k, error_code & ec)
 inline void unset(const key & k)
 {
   error_code ec;
   detail::unset(k, ec);
   BOOST_PROCESS_V2_NAMESPACE::detail::throw_error(ec, "environment::unset");
 }
 
 /// Disambiguating @overload void unset(const key & k, error_code & ec)
 inline void unset(basic_cstring_ref<char_type, key_char_traits<char_type>> k, error_code & ec)
 {
   detail::unset(k, ec);
 }
 
 /// Disambiguating @overload void unset(const key & k, error_code & ec)
 inline void unset(basic_cstring_ref<char_type, key_char_traits<char_type>> k)
 {
   error_code ec;
   detail::unset(k, ec);
   BOOST_PROCESS_V2_NAMESPACE::detail::throw_error(ec, "environment::unset");
 }
 
 /// Disambiguating @overload void unset(const key & k, error_code & ec)
 inline void unset(const char_type * c, error_code & ec) { detail::unset(c, ec);}
 
 /// Disambiguating @overload void unset(const key & k, error_code & ec)
 inline void unset(const char_type * c)
 {
   error_code ec;
   detail::unset(c, ec);
   BOOST_PROCESS_V2_NAMESPACE::detail::throw_error(ec, "environment::unset");
 }
 }
 
 // sub process environment stuff
 
 #if defined(BOOST_PROCESS_V2_WINDOWS)
 namespace windows { struct default_launcher ;}
 #else
 namespace posix { struct default_launcher ;}
 #endif 
 
 /// Initializer for the environment of sub process.
 /**
  * This will set the environment in a subprocess:
  * 
  * @code {.cpp}
  * 
  * process proc{executor, find_executable("printenv"), {"foo"}, process_environment{"foo=bar"}};
  * @endcode
  * 
  * The environment initializer will persist it's state, so that it can
  * be used multiple times. Do however note the the Operating System is
  * allowed to modify the internal state.
  * 
  * @code {.cpp}
  * auto exe = find_executable("printenv");
  * process_environment env = {"FOO=BAR", "BAR=FOO"};
  * 
  * process proc1(executor, exe, {"FOO"}, env);
  * process proc2(executor, exe, {"BAR"}, env);
  * @endcode
  * 
  * 
  */
 struct process_environment
 {
 
 #if defined(BOOST_PROCESS_V2_WINDOWS)
 
 
   template<typename Args>
   static
   std::vector<wchar_t> build_env(Args && args,
                                       typename std::enable_if<
                                               std::is_convertible<
                                                       decltype(*std::begin(std::declval<Args>())),
                                                       wcstring_ref>::value>::type * = nullptr)
   {
     std::vector<wchar_t> res;
     std::size_t sz = 1;
     for (wcstring_ref cs : std::forward<Args>(args))
         sz =+ cs.size() + 1;
     res.reserve(sz);
     
     for (wcstring_ref cs : std::forward<Args>(args))
         res.insert(res.end(), cs.begin(), std::next(cs.end()));
         
 
     res.push_back(L'\0');
     return res;
   }
 
   template<typename Args>
   std::vector<wchar_t> build_env(Args && args,
                                       typename std::enable_if<
                                               !std::is_convertible<
                                                       decltype(*std::begin(std::declval<Args>())),
                                                       wcstring_ref>::value>::type * = nullptr)
   {
     for (auto && arg: std::forward<Args>(args))
       env_buffer.emplace_back(arg);
     return build_env(env_buffer);
   }
 
   process_environment(std::initializer_list<string_view> sv)  : unicode_env{build_env(sv)} {}
   process_environment(std::initializer_list<wstring_view> sv) : unicode_env{build_env(sv)} {}
 
   template<typename Args>
   process_environment(Args && args) : unicode_env{build_env(std::forward<Args>(args))}
   {
   }
 
   error_code error() {return ec;}
   error_code ec;
   std::vector<environment::key_value_pair> env_buffer;
   std::vector<wchar_t> unicode_env;
 
   BOOST_PROCESS_V2_DECL
   error_code on_setup(windows::default_launcher & launcher,
                       const filesystem::path &, const std::wstring &);
 
 #else
 
   template<typename Args>
   static
   std::vector<const char *> build_env(Args && args,
                                       typename std::enable_if<
                                               std::is_convertible<
                                                       decltype(*std::begin(std::declval<Args>())),
                                                       cstring_ref>::value>::type * = nullptr)
   {
     std::vector<const char *> env;
     for (auto && e : args)
       env.push_back(e.c_str());
 
     env.push_back(nullptr);
     return env;
   }
 
   template<typename Args>
   std::vector<const char *> build_env(Args && args,
                                       typename std::enable_if<
                                               !std::is_convertible<
                                                       decltype(*std::begin(std::declval<Args>())),
                                                       cstring_ref>::value>::type * = nullptr)
   {
     std::vector<const char *> env;
 
     for (auto && arg: std::forward<Args>(args))
       env_buffer.emplace_back(arg);
 
     for (auto && e : env_buffer)
       env.push_back(e.c_str());
     env.push_back(nullptr);
     return env;
   }
 
 
   process_environment(std::initializer_list<string_view> sv) : env{build_env(sv)}  {  }
 
   template<typename Args>
   process_environment(Args && args) : env(build_env(std::forward<Args>(args)))
   {
   }
 
 
   BOOST_PROCESS_V2_DECL
   error_code on_setup(posix::default_launcher & launcher, 
                       const filesystem::path &, const char * const *);
 
   std::vector<environment::key_value_pair> env_buffer;
   std::vector<const char *> env;
 
 #endif
 
 };
 
 
 
 BOOST_PROCESS_V2_END_NAMESPACE
 
 
 namespace std
 {
 
 template<>
 struct hash<BOOST_PROCESS_V2_NAMESPACE::environment::key_view>
 {
     std::size_t operator()( BOOST_PROCESS_V2_NAMESPACE::environment::key_view kv) const noexcept
     {
         return BOOST_PROCESS_V2_NAMESPACE::environment::hash_value(kv);
     }
 };
 
 
 template<>
 struct hash<BOOST_PROCESS_V2_NAMESPACE::environment::value_view>
 {
     std::size_t operator()( BOOST_PROCESS_V2_NAMESPACE::environment::value_view kv) const noexcept
     {
         return BOOST_PROCESS_V2_NAMESPACE::environment::hash_value(kv);
     }
 };
 
 template<>
 struct hash<BOOST_PROCESS_V2_NAMESPACE::environment::key_value_pair_view>
 {
     std::size_t operator()( BOOST_PROCESS_V2_NAMESPACE::environment::key_value_pair_view kv) const noexcept
     {
         return BOOST_PROCESS_V2_NAMESPACE::environment::hash_value(kv);
     }
 };
 
 
 template<>
 struct hash<BOOST_PROCESS_V2_NAMESPACE::environment::key>
 {
     std::size_t operator()( BOOST_PROCESS_V2_NAMESPACE::environment::key_view kv) const noexcept
     {
         return BOOST_PROCESS_V2_NAMESPACE::environment::hash_value(kv);
     }
 };
 
 
 template<>
 struct hash<BOOST_PROCESS_V2_NAMESPACE::environment::value>
 {
     std::size_t operator()( BOOST_PROCESS_V2_NAMESPACE::environment::value_view kv) const noexcept
     {
         return BOOST_PROCESS_V2_NAMESPACE::environment::hash_value(kv);
     }
 };
 
 template<>
 struct hash<BOOST_PROCESS_V2_NAMESPACE::environment::key_value_pair>
 {
     std::size_t operator()( BOOST_PROCESS_V2_NAMESPACE::environment::key_value_pair_view kv) const noexcept
     {
         return BOOST_PROCESS_V2_NAMESPACE::environment::hash_value(kv);
     }
 };
 
 }
 
 
 
 #if defined(BOOST_PROCESS_V2_HEADER_ONLY)
 
 #include <boost/process/v2/impl/environment.ipp>
 #include <boost/process/v2/detail/impl/environment.ipp>
 
 #endif
 
 #endif //BOOST_PROCESS_V2_ENVIRONMENT_HPP