refactor: drop Boost.Move dependency

Implement constexpr definitions of forward and move to replace usage
of boost::move and boost::forward from the Boost.Move library.

Alter tests to use std::move instead of boost::move.

Remove the dependency on Boost.Move from build.jam

include/boost/optional/detail/optional_reference_spec.hpp

@@ -39,7 +39,7 @@ BOOST_DEDUCED_TYPENAME boost::remove_reference<T>::type& forward_reference(T&& r
 {
     BOOST_STATIC_ASSERT_MSG(boost::is_lvalue_reference<T>::value,
                             "binding rvalue references to optional lvalue references is disallowed");
-    return boost::forward<T>(r);
+    return optional_detail::forward<T>(r);
 }
 
 #endif // BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES

include/boost/optional/detail/optional_swap.hpp

@@ -54,7 +54,7 @@ struct swap_selector<true>
 #endif
 
 #ifndef BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
-# define BOOST_OPTIONAL_DETAIL_MOVE(EXPR_) boost::move(EXPR_)
+# define BOOST_OPTIONAL_DETAIL_MOVE(EXPR_) optional_detail::move(EXPR_)
 #else
 # define BOOST_OPTIONAL_DETAIL_MOVE(EXPR_) EXPR_
 #endif

include/boost/optional/detail/optional_trivially_copyable_base.hpp

@@ -54,7 +54,7 @@ class tc_optional_base : public optional_tag
       :
       m_initialized(false)
     {
-      construct(boost::forward<Expr>(expr),tag);
+      construct(optional_detail::forward<Expr>(expr),tag);
     }
 
     // tc_optional_base& operator= ( tc_optional_base const& ) = default;
@@ -102,7 +102,7 @@ class tc_optional_base : public optional_tag
     template<class Expr, class ExprPtr>
     void assign_expr ( Expr&& expr, ExprPtr const* tag )
     {
-       construct(boost::forward<Expr>(expr),tag);
+       construct(optional_detail::forward<Expr>(expr),tag);
     }
 
 #endif
@@ -138,14 +138,14 @@ class tc_optional_base : public optional_tag
     template<class... Args>
     void construct ( in_place_init_t, Args&&... args )
     {
-      m_storage = value_type( boost::forward<Args>(args)... ) ;
+      m_storage = value_type( optional_detail::forward<Args>(args)... ) ;
       m_initialized = true ;
     }
 
     template<class... Args>
     void emplace_assign ( Args&&... args )
     {
-      construct(in_place_init, boost::forward<Args>(args)...);
+      construct(in_place_init, optional_detail::forward<Args>(args)...);
     }
 
     template<class... Args>
@@ -153,7 +153,7 @@ class tc_optional_base : public optional_tag
       :
       m_initialized(false)
     {
-      construct(in_place_init, boost::forward<Args>(args)...);
+      construct(in_place_init, optional_detail::forward<Args>(args)...);
     }
 
     template<class... Args>
@@ -162,7 +162,7 @@ class tc_optional_base : public optional_tag
       m_initialized(false)
     {
       if ( cond )
-        construct(in_place_init, boost::forward<Args>(args)...);
+        construct(in_place_init, optional_detail::forward<Args>(args)...);
     }
 
 #ifndef BOOST_OPTIONAL_NO_INPLACE_FACTORY_SUPPORT
@@ -207,7 +207,7 @@ class tc_optional_base : public optional_tag
     template<class Expr>
     void construct ( Expr&& expr, void const* )
     {
-      m_storage = value_type(boost::forward<Expr>(expr)) ;
+      m_storage = value_type(optional_detail::forward<Expr>(expr)) ;
       m_initialized = true ;
     }
 
@@ -218,7 +218,7 @@ class tc_optional_base : public optional_tag
     template<class Expr>
     void assign_expr_to_initialized ( Expr&& expr, void const* )
     {
-      assign_value( boost::forward<Expr>(expr) );
+      assign_value( optional_detail::forward<Expr>(expr) );
     }
 
 #ifdef BOOST_OPTIONAL_WEAK_OVERLOAD_RESOLUTION
@@ -243,7 +243,7 @@ class tc_optional_base : public optional_tag
        {
          // An exception can be thrown here.
          // It it happens, THIS will be left uninitialized.
-         m_storage = value_type(boost::move(expr.get())) ;
+         m_storage = value_type(optional_detail::move(expr.get())) ;
          m_initialized = true ;
        }
      }

include/boost/optional/detail/optional_utility.hpp

@@ -0,0 +1,38 @@
+// Copyright (C) 2024 Andrzej Krzemienski.
+//
+// Use, modification, and distribution is subject to 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)
+//
+// See http://www.boost.org/libs/optional for documentation.
+//
+// You are welcome to contact the author at:
+//  akrzemi1@gmail.com
+
+#ifndef BOOST_OPTIONAL_OPTIONAL_DETAIL_OPTIONAL_UTILITY_HPP
+#define BOOST_OPTIONAL_OPTIONAL_DETAIL_OPTIONAL_UTILITY_HPP
+
+namespace boost {
+namespace optional_detail {
+
+// Workaround: forward and move aren't constexpr in C++11
+template <class T> inline constexpr T&& forward(typename boost::remove_reference<T>::type& t) noexcept
+{
+  return static_cast<T&&>(t);
+}
+
+template <class T> inline constexpr T&& forward(typename boost::remove_reference<T>::type&& t) noexcept
+{
+  BOOST_STATIC_ASSERT_MSG(!boost::is_lvalue_reference<T>::value, "Can not forward an rvalue as an lvalue.");
+  return static_cast<T&&>(t);
+}
+
+template <class T> inline constexpr typename boost::remove_reference<T>::type&& move(T&& t) noexcept
+{
+  return static_cast<typename boost::remove_reference<T>::type&&>(t);
+}
+
+} // namespace optional_detail
+} // namespace boost
+
+#endif