is_placeholder, is_bind_expression added.

[SVN r34468]

include/boost/bind/arg.hpp

@@ -19,18 +19,44 @@
 //  See http://www.boost.org/libs/bind/bind.html for documentation.
 //
 
+#include <boost/config.hpp>
+#include <boost/is_placeholder.hpp>
+
 namespace boost
 {
 
-template<int I> class arg
+template< int I > struct arg
 {
+    arg()
+    {
+    }
+
+    template< class T > arg( T const & /* t */ )
+    {
+        // static assert I == is_placeholder<T>::value
+        typedef char T_must_be_placeholder[ I == is_placeholder<T>::value? 1: -1 ];
+    }
 };
 
-template<int I> bool operator==(arg<I> const &, arg<I> const &)
+template< int I > bool operator==( arg<I> const &, arg<I> const & )
 {
     return true;
 }
 
+#if !defined( BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION )
+
+template< int I > struct is_placeholder< arg<I> >
+{
+    enum _vt { value = I };
+};
+
+template< int I > struct is_placeholder< arg<I> (*) () >
+{
+    enum _vt { value = I };
+};
+
+#endif
+
 } // namespace boost
 
 #endif // #ifndef BOOST_BIND_ARG_HPP_INCLUDED