整理

include/boost/iterator/detail/config_def.hpp

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+// (C) Copyright David Abrahams 2002.
+// (C) Copyright Jeremy Siek    2002.
+// (C) Copyright Thomas Witt    2002.
+// Distributed under 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)
+
+// no include guard multiple inclusion intended
+
+//
+// This is a temporary workaround until the bulk of this is
+// available in boost config.
+// 23/02/03 thw
+//
+
+#include <boost/config.hpp> // for prior
+#include <boost/detail/workaround.hpp>
+
+#ifdef BOOST_ITERATOR_CONFIG_DEF
+# error you have nested config_def #inclusion.
+#else
+# define BOOST_ITERATOR_CONFIG_DEF
+#endif
+
+// We enable this always now.  Otherwise, the simple case in
+// libs/iterator/test/constant_iterator_arrow.cpp fails to compile
+// because the operator-> return is improperly deduced as a non-const
+// pointer.
+
+// Recall that in general, compilers without partial specialization
+// can't strip constness.  Consider counting_iterator, which normally
+// passes a const Value to iterator_facade.  As a result, any code
+// which makes a std::vector of the iterator's value_type will fail
+// when its allocator declares functions overloaded on reference and
+// const_reference (the same type).
+//
+// Furthermore, Borland 5.5.1 drops constness in enough ways that we
+// end up using a proxy for operator[] when we otherwise shouldn't.
+// Using reference constness gives it an extra hint that it can
+// return the value_type from operator[] directly, but is not
+// strictly necessary.  Not sure how best to resolve this one.
+
+# define BOOST_ITERATOR_REF_CONSTNESS_KILLS_WRITABILITY 1
+
+// no include guard; multiple inclusion intended