1 files changed, 89 insertions, 0 deletions
diff --git a/boost/parameter/aux_/pack/tag_type.hpp b/boost/parameter/aux_/pack/tag_type.hpp
new file mode 100644
index 0000000000..81d1a1476f
--- /dev/null
+++ b/boost/parameter/aux_/pack/tag_type.hpp
@@ -0,0 +1,89 @@
+// Copyright David Abrahams, Daniel Wallin 2003.
+// 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_PARAMETER_AUX_PACK_TAG_TYPE_HPP
+#define BOOST_PARAMETER_AUX_PACK_TAG_TYPE_HPP
+
+namespace boost { namespace parameter { namespace aux {
+
+    // helper for tag_type<...>, below.
+    template <typename T>
+    struct get_tag_type0
+    {
+        typedef typename T::key_type type;
+    };
+}}} // namespace boost::parameter::aux
+
+#include <boost/parameter/deduced.hpp>
+#include <boost/parameter/config.hpp>
+
+#if defined(BOOST_PARAMETER_CAN_USE_MP11)
+#include <boost/mp11/utility.hpp>
+#else
+#include <boost/mpl/eval_if.hpp>
+#endif
+
+namespace boost { namespace parameter { namespace aux {
+
+    template <typename T>
+    struct get_tag_type
+#if defined(BOOST_PARAMETER_CAN_USE_MP11)
+      : ::boost::mp11::mp_if<
+#else
+      : ::boost::mpl::eval_if<
+#endif
+            ::boost::parameter::aux::is_deduced0<T>
+          , ::boost::parameter::aux::get_tag_type0<typename T::key_type>
+          , ::boost::parameter::aux::get_tag_type0<T>
+        >
+    {
+    };
+}}} // namespace boost::parameter::aux
+
+#include <boost/parameter/required.hpp>
+#include <boost/parameter/optional.hpp>
+
+#if defined(BOOST_PARAMETER_CAN_USE_MP11)
+#include <boost/mp11/integral.hpp>
+
+namespace boost { namespace parameter { namespace aux {
+
+    template <typename T>
+    using tag_type = ::boost::mp11::mp_if<
+        ::boost::mp11::mp_if<
+            ::boost::parameter::aux::is_optional<T>
+          , ::boost::mp11::mp_true
+          , ::boost::parameter::aux::is_required<T>
+        >
+      , ::boost::parameter::aux::get_tag_type<T>
+      , ::boost::mp11::mp_identity<T>
+    >;
+}}} // namespace boost::parameter::aux
+
+#else   // !defined(BOOST_PARAMETER_CAN_USE_MP11)
+#include <boost/mpl/bool.hpp>
+#include <boost/mpl/if.hpp>
+#include <boost/mpl/identity.hpp>
+
+namespace boost { namespace parameter { namespace aux {
+
+    template <typename T>
+    struct tag_type
+      : ::boost::mpl::eval_if<
+            typename ::boost::mpl::if_<
+                ::boost::parameter::aux::is_optional<T>
+              , ::boost::mpl::true_
+              , ::boost::parameter::aux::is_required<T>
+            >::type
+          , ::boost::parameter::aux::get_tag_type<T>
+          , ::boost::mpl::identity<T>
+        >
+    {
+    };
+}}} // namespace boost::parameter::aux
+
+#endif  // BOOST_PARAMETER_CAN_USE_MP11
+#endif  // include guard
+