Imported Upstream version 1.57.0upstream/1.57.0

1 files changed, 53 insertions, 0 deletions

diff --git a/boost/type_erasure/deduced.hpp b/boost/type_erasure/deduced.hpp
new file mode 100644
index 0000000000..b9ed96094c
--- /dev/null
+++ b/boost/type_erasure/deduced.hpp
@@ -0,0 +1,53 @@
+// Boost.TypeErasure library
+//
+// Copyright 2011 Steven Watanabe
+//
+// 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)
+//
+// $Id$
+
+#ifndef BOOST_TYPE_ERASURE_DEDUCED_HPP_INCLUDED
+#define BOOST_TYPE_ERASURE_DEDUCED_HPP_INCLUDED
+
+#include <boost/mpl/eval_if.hpp>
+#include <boost/mpl/identity.hpp>
+#include <boost/mpl/set.hpp>
+#include <boost/mpl/empty.hpp>
+#include <boost/type_erasure/detail/get_placeholders.hpp>
+#include <boost/type_erasure/placeholder.hpp>
+
+namespace boost {
+namespace type_erasure {
+
+/**
+ * A placeholder for an associated type.  The type corresponding
+ * to this placeholder is deduced by substituting placeholders
+ * in the arguments of the metafunction and then evaluating it.
+ * 
+ * When using @ref deduced in a template context, if it is possible for
+ * Metafunction to contain no placeholders at all, use the nested type,
+ * to automatically evaluate it early as needed.
+ */
+template<class Metafunction>
+struct deduced : ::boost::type_erasure::placeholder
+{
+    typedef typename ::boost::mpl::eval_if<
+        ::boost::mpl::empty<
+            typename ::boost::type_erasure::detail::get_placeholders<
+                Metafunction,
+                ::boost::mpl::set0<>
+            >::type
+        >,
+        Metafunction,
+        ::boost::mpl::identity<
+            ::boost::type_erasure::deduced<Metafunction>
+        >
+    >::type type;
+};
+
+}
+}
+
+#endif