Resolve C++20 issue with fn == bind(...). Fixes #45.

include/boost/function/detail/epilogue.hpp

@@ -0,0 +1,39 @@
+// Boost.Function library
+
+#ifndef BOOST_FUNCTION_EPILOGUE_HPP
+#define BOOST_FUNCTION_EPILOGUE_HPP
+
+// Copyright 2023 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+// Resolve C++20 issue with fn == bind(...)
+// https://github.com/boostorg/function/issues/45
+
+#if !defined(BOOST_FUNCTION_NO_FUNCTION_TYPE_SYNTAX)
+
+namespace boost
+{
+
+namespace _bi
+{
+
+template<class R, class F, class L> class bind_t;
+
+} // namespace _bi
+
+template<class S, class R, class F, class L> bool operator==( function<S> const& f, _bi::bind_t<R, F, L> const& b )
+{
+    return f.contains( b );
+}
+
+template<class S, class R, class F, class L> bool operator!=( function<S> const& f, _bi::bind_t<R, F, L> const& b )
+{
+    return !f.contains( b );
+}
+
+} // namespace boost
+
+#endif // #if !defined(BOOST_FUNCTION_NO_FUNCTION_TYPE_SYNTAX)
+
+#endif // #ifndef BOOST_FUNCTION_EPILOGUE_HPP