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Why not compromise? 1. Make the lexical_cast changes for optional that Andrew Troschinetz suggested. 2. Add the following convert_to.hpp file: #include <boost/lexical_cast.hpp> #include <boost/optional.hpp> namespace boost { template <typename Target, typename Source> inline Target convert_to(const Source& arg) { return lexical_cast< optional<Target> >(arg).get_value_or(Target()); } template <typename Target, typename Source> inline Target convert_to(const Source& arg, const Target& fallback) { return lexical_cast< optional<Target> >(arg).get_value_or(fallback); } } 3. Use convert_to instead of lexical_cast. 4. Everyone happy? Regards, Anders Dalvander