Improve MQTT_STD_XXX behavior

include/mqtt/broker/retained_topic_map.hpp

@@ -358,7 +358,7 @@ class retained_topic_map {
     void dump(Output &out) {
         auto const& direct_index = map.template get<direct_index_tag>();
         for (auto const& i : direct_index) {
-            out << i.parent_id << " " << i.name << " " << (i.value ? "init" : "-") << " " << i.count << std::endl;
+            out << i.parent_id << " " << i.name << " " << (i.value ? "init" : "-") << " " << i.count << '\n';
         }
     }
 

include/mqtt/broker/security.hpp

@@ -19,7 +19,6 @@
 
 #include <boost/property_tree/ptree.hpp>
 #include <boost/property_tree/json_parser.hpp>
-#include <boost/optional.hpp>
 #include <boost/iterator/function_output_iterator.hpp>
 
 #include <boost/algorithm/hex.hpp>
@@ -595,27 +594,17 @@ struct security {
 
             if (is_hash(auth)) {
                 append_result(
-                    string_view(
+                    make_string_view(
                         subscription_begin,
-                        static_cast<size_t>(
-                            std::distance(
-                                subscription_begin,
-                                subscription_filter.end()
-                            )
-                        )
+                        subscription_filter.end()
                     )
                 );
                 return result;
             }
 
-            auto sub = string_view(
+            auto sub = make_string_view(
                 subscription_begin,
-                static_cast<size_t>(
-                    std::distance(
-                        subscription_begin,
-                        subscription_next
-                    )
-                )
+                subscription_next
             );
 
             if (is_hash(sub)) {

include/mqtt/broker/topic_filter.hpp

@@ -43,9 +43,10 @@ inline std::size_t topic_filter_tokenizer(string_view str, Output write) {
         std::end(str),
         [&write](string_view::const_iterator token_begin, string_view::const_iterator token_end) {
             return write(
-                string_view(
+                make_string_view(
                     token_begin,
-                    static_cast<std::size_t>(std::distance(token_begin, token_end)))
+                    token_end
+                )
             );
         }
     );

include/mqtt/endpoint.hpp

@@ -19,7 +19,6 @@
 #include <atomic>
 #include <algorithm>
 
-#include <boost/any.hpp>
 #include <boost/lexical_cast.hpp>
 #include <boost/asio.hpp>
 #include <boost/lexical_cast.hpp>
@@ -149,7 +148,7 @@ constexpr bool check_qos_value(publish_options pubopts) {
 
 template<typename ... Params>
 constexpr bool should_generate_packet_id(Params const& ... params) {
-#if __cplusplus >= 201703L // C++20 date is not determined yet
+#if __cplusplus >= 201703L
     return (check_qos_value(params) || ...); // defaults to false for empty.
 #else  // __cplusplus >= 201703L
     const bool results[] = {false, check_qos_value(params)... };

include/mqtt/shared_ptr_array.hpp

@@ -47,11 +47,11 @@ using shared_ptr_array = std::shared_ptr<char []>;
 using const_shared_ptr_array = std::shared_ptr<char const []>;
 
 inline shared_ptr_array make_shared_ptr_array(std::size_t size) {
-#if __cplusplus > 201703L // C++20 date is not determined yet
+#if __cpp_lib_shared_ptr_arrays >= 201707L
     return std::make_shared<char[]>(size);
-#else  // __cplusplus > 201703L
+#else  // __cpp_lib_shared_ptr_arrays >= 201707L
     return std::shared_ptr<char[]>(new char[size]);
-#endif // __cplusplus > 201703L
+#endif // __cpp_lib_shared_ptr_arrays >= 201707L
 }
 
 } // namespace MQTT_NS

include/mqtt/string_view.hpp

@@ -7,6 +7,8 @@
 #if !defined(MQTT_STRING_VIEW_HPP)
 #define MQTT_STRING_VIEW_HPP
 
+#include <iterator>
+
 #include <mqtt/namespace.hpp>
 
 #ifdef MQTT_STD_STRING_VIEW
@@ -75,4 +77,30 @@ using basic_string_view = boost::basic_string_ref<CharT, Traits>;
 
 #endif // !defined(MQTT_STD_STRING_VIEW)
 
+namespace MQTT_NS {
+
+namespace detail {
+
+template<class T>
+T* to_address(T* p) noexcept
+{
+    return p;
+}
+
+template<class T>
+auto to_address(const T& p) noexcept
+{
+    return detail::to_address(p.operator->());
+}
+
+} // namespace detail
+
+// Make a string_view from a pair of iterators.
+template<typename Begin, typename End>
+string_view make_string_view(Begin begin, End end) {
+    return string_view(detail::to_address(begin), static_cast<string_view::size_type>(std::distance(begin, end)));
+}
+
+} // namespace MQTT_NS
+
 #endif // MQTT_STRING_VIEW_HPP

include/mqtt/v5_message.hpp

@@ -14,7 +14,6 @@
 #include <numeric>
 
 #include <boost/asio/buffer.hpp>
-#include <boost/optional.hpp>
 #include <boost/container/static_vector.hpp>
 #include <boost/numeric/conversion/cast.hpp>
 
@@ -37,6 +36,7 @@
 #include <mqtt/packet_id_type.hpp>
 #include <mqtt/move.hpp>
 #include <mqtt/variant_visit.hpp>
+#include <mqtt/optional.hpp>
 
 #if !defined(MQTT_ALWAYS_SEND_REASON_CODE)
 #define MQTT_ALWAYS_SEND_REASON_CODE false