Hi, I was wondering if we can add the declval utility function template to the Boost.Utility library 20.3.4 Function template declval [declval] 1 The library provides the function template declval to simplify the definition of expressions which occur as unevaluated operands (Clause 5). template <class T> typename add_rvalue_reference<T>::type declval() noexcept; // as unevaluated operand 2 Remarks: If this function is used (as defined by (3.2)), the program is ill-formed. 3 Remarks: The template parameter T of declval may be an incomplete type. [ Example: template <class To, class From> decltype(static_cast<To>(declval<From>())) convert(From&&); declares a function template convert which only participats in overloading if the type From can be explicitly converted to type To. For another example see class template common_type (20.7.6.6). -end example ] BTW, add_rvalue_reference is not available on Boost.TypeTraits, add_rvalue_reference_layer. Any problem to add it? Best, _____________________ Vicente Juan Botet Escribá http://viboes.blogspot.com/