Add arg_iter and arg_view.

include/boost/program_options_2/parse_command_line.hpp

@@ -62,6 +62,44 @@ namespace boost { namespace program_options_2 {
         std::string_view help_description = "Print this help message and exit";
     };
 
+    /** TODO */
+    template<typename Char>
+    struct arg_iter : stl_interfaces::proxy_iterator_interface<
+                          arg_iter<Char>,
+                          std::random_access_iterator_tag,
+                          std::basic_string_view<Char>>
+    {
+        arg_iter() = default;
+        arg_iter(Char const ** ptr) : it_(ptr) { BOOST_ASSERT(ptr); }
+
+        std::basic_string_view<Char> operator*() const { return {*it_}; }
+
+    private:
+        friend boost::stl_interfaces::access;
+        Char const **& base_reference() noexcept { return it_; }
+        Char const ** base_reference() const noexcept { return it_; }
+        Char const ** it_;
+    };
+
+    /** TODO */
+    template<typename Char>
+    struct arg_view : stl_interfaces::view_interface<arg_view<Char>>
+    {
+        using iterator = arg_iter<Char>;
+
+        arg_view() = default;
+        arg_view(int argc, Char const ** argv) :
+            first_(argv), last_(argv + argc)
+        {}
+
+        iterator begin() const { return first_; }
+        iterator end() const { return last_; }
+
+    private:
+        iterator first_;
+        iterator last_;
+    };
+
     namespace detail {
         template<typename BidiIter, typename T>
         BidiIter find_last(BidiIter first, BidiIter last, T const & x)