Support use of standard placeholders with boost::bind

test/Jamfile.v2

@@ -78,3 +78,4 @@ run bind_cpp20_test.cpp ;
 run protect_test2.cpp ;
 run protect_cpp20_test.cpp ;
 run bind_noexcept_mf2_test.cpp ;
+run std_placeholders_test.cpp ;

test/std_placeholders_test.cpp

@@ -0,0 +1,50 @@
+// Copyright 2021 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/bind/bind.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <functional>
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if defined(BOOST_NO_CXX11_HDR_FUNCTIONAL)
+
+BOOST_PRAGMA_MESSAGE( "Skipping test due to BOOST_NO_CXX11_HDR_FUNCTIONAL being defined" )
+int main() {}
+
+#elif defined(BOOST_NO_CXX11_DECLTYPE)
+
+BOOST_PRAGMA_MESSAGE( "Skipping test due to BOOST_NO_CXX11_DECLTYPE being defined" )
+int main() {}
+
+#elif defined(BOOST_NO_CXX11_HDR_TYPE_TRAITS)
+
+BOOST_PRAGMA_MESSAGE( "Skipping test due to BOOST_NO_CXX11_HDR_TYPE_TRAITS being defined" )
+int main() {}
+
+#else
+
+int f( int x )
+{
+    return -x;
+}
+
+int main()
+{
+    using namespace std::placeholders;
+
+    BOOST_TEST_EQ( boost::bind( f, _1 )( 1 ), -1 );
+    BOOST_TEST_EQ( boost::bind( f, _2 )( 1, 2 ), -2 );
+    BOOST_TEST_EQ( boost::bind( f, _3 )( 1, 2, 3 ), -3 );
+    BOOST_TEST_EQ( boost::bind( f, _4 )( 1, 2, 3, 4 ), -4 );
+    BOOST_TEST_EQ( boost::bind( f, _5 )( 1, 2, 3, 4, 5 ), -5 );
+    BOOST_TEST_EQ( boost::bind( f, _6 )( 1, 2, 3, 4, 5, 6 ), -6 );
+    BOOST_TEST_EQ( boost::bind( f, _7 )( 1, 2, 3, 4, 5, 6, 7 ), -7 );
+    BOOST_TEST_EQ( boost::bind( f, _8 )( 1, 2, 3, 4, 5, 6, 7, 8 ), -8 );
+    BOOST_TEST_EQ( boost::bind( f, _9 )( 1, 2, 3, 4, 5, 6, 7, 8, 9 ), -9 );
+
+    return boost::report_errors();
+}
+
+#endif