Support use of standard placeholders with boost::bind

include/boost/bind/bind.hpp

@@ -28,6 +28,7 @@
 #include <boost/is_placeholder.hpp>
 #include <boost/bind/arg.hpp>
 #include <boost/bind/detail/result_traits.hpp>
+#include <boost/bind/std_placeholders.hpp>
 #include <boost/detail/workaround.hpp>
 #include <boost/visit_each.hpp>
 #include <boost/core/enable_if.hpp>

include/boost/bind/std_placeholders.hpp

@@ -0,0 +1,39 @@
+#ifndef BOOST_BIND_STD_PLACEHOLDERS_HPP_INCLUDED
+#define BOOST_BIND_STD_PLACEHOLDERS_HPP_INCLUDED
+
+// MS compatible compilers support #pragma once
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1020)
+# pragma once
+#endif
+
+// Copyright 2021 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/is_placeholder.hpp>
+#include <boost/config.hpp>
+
+#if !defined(BOOST_NO_CXX11_HDR_FUNCTIONAL) && !defined(BOOST_NO_CXX11_DECLTYPE) && !defined(BOOST_NO_CXX11_HDR_TYPE_TRAITS)
+
+#include <functional>
+#include <type_traits>
+
+namespace boost
+{
+
+template<> struct is_placeholder< typename std::decay<decltype(std::placeholders::_1)>::type > { enum _vt { value = 1 }; };
+template<> struct is_placeholder< typename std::decay<decltype(std::placeholders::_2)>::type > { enum _vt { value = 2 }; };
+template<> struct is_placeholder< typename std::decay<decltype(std::placeholders::_3)>::type > { enum _vt { value = 3 }; };
+template<> struct is_placeholder< typename std::decay<decltype(std::placeholders::_4)>::type > { enum _vt { value = 4 }; };
+template<> struct is_placeholder< typename std::decay<decltype(std::placeholders::_5)>::type > { enum _vt { value = 5 }; };
+template<> struct is_placeholder< typename std::decay<decltype(std::placeholders::_6)>::type > { enum _vt { value = 6 }; };
+template<> struct is_placeholder< typename std::decay<decltype(std::placeholders::_7)>::type > { enum _vt { value = 7 }; };
+template<> struct is_placeholder< typename std::decay<decltype(std::placeholders::_8)>::type > { enum _vt { value = 8 }; };
+template<> struct is_placeholder< typename std::decay<decltype(std::placeholders::_9)>::type > { enum _vt { value = 9 }; };
+
+} // namespace boost
+
+#endif
+
+#endif // #ifndef BOOST_BIND_STD_PLACEHOLDERS_HPP_INCLUDED