From 201a7e20d0a14c41f234ea4fbc25f19de8dae213 Mon Sep 17 00:00:00 2001
From: Andrey Semashev <andrey.semashev@gmail.com>
Date: Sun, 15 Mar 2020 18:13:07 +0300
Subject: [PATCH] Fix argument value selection with an rvalue default.

In C++11 mode, when named parameter pack was a single tagged argument,
parameter value was not extracted when an rvalue default value was
provided by the user (instead, the default value was returned). This
commit adds a missing overload for default_r_, which returns the parameter
value.

Fixes https://github.com/boostorg/parameter/issues/97.
---
 include/boost/parameter/aux_/tagged_argument.hpp | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/include/boost/parameter/aux_/tagged_argument.hpp b/include/boost/parameter/aux_/tagged_argument.hpp
index 964dd8f..bdc1eb1 100644
--- a/include/boost/parameter/aux_/tagged_argument.hpp
+++ b/include/boost/parameter/aux_/tagged_argument.hpp
@@ -295,6 +295,15 @@ namespace boost { namespace parameter { namespace aux {
             return this->get_value();
         }
 
+        template <typename Default>
+        inline BOOST_CONSTEXPR reference
+            operator[](
+                ::boost::parameter::aux::default_r_<key_type,Default> const&
+            ) const
+        {
+            return this->get_value();
+        }
+
         template <typename F>
         inline BOOST_CONSTEXPR reference
             operator[](
@@ -662,7 +671,7 @@ namespace boost { namespace parameter { namespace aux {
             ::boost::parameter::aux::tagged_argument<Keyword,Arg>
           , ::boost::parameter::aux::arg_list<
                 ::boost::parameter::aux::tagged_argument<Keyword2,Arg2>
-            > 
+            >
         >
             operator,(
                 ::boost::parameter::aux
@@ -673,7 +682,7 @@ namespace boost { namespace parameter { namespace aux {
                 ::boost::parameter::aux::tagged_argument<Keyword,Arg>
               , ::boost::parameter::aux::arg_list<
                     ::boost::parameter::aux::tagged_argument<Keyword2,Arg2>
-                > 
+                >
             >(
                 *this
               , ::boost::parameter::aux::arg_list<