On Tuesday 04 September 2012 11:07:39 you wrote:
Jeffrey have suggested a good solution in his reply. I think it can be described in the result_of docs to resolve the confusion in the future. I can update the docs if noone objects.
I've added a clarification note to the result_of docs in trunk. Here is the added section: <quote> The result template must be specialized for every valid calling signature of the function object. If the operator() accepts arguments by (possibly const) reference and/or is const qualified, the result specialization must take this into account. Type traits and more generic specializations may help to reduce the number of result specializations. This way result_of users will be able to specify argument types exactly according to the function object call expression. For example: struct functor { template<class> struct result; // Use template parameter F to match the function object. This will allow result deduction for both const and non-const functor. template<class F, class T> struct result<F(T)> { // When argument type is matched like above, remember that the type may be a (const-qualified) reference. // Use type traits to transform the argument type. typedef typename remove_cv<typename remove_reference<T>::type>::type argument_type; typedef argument_type type; }; // The operator can be called on both const and non-const functor. The argument can be lvalue or rvalue. template<class T> T operator()(T const& x) const { return x; } }; // All following result_of uses are valid and result in int typedef boost::result_of< functor(int) >::type type1; // the argument is rvalue functor f; type1 r1 = f(10); typedef boost::result_of< const functor(int) >::type type2; // the function object is const const functor cf; type2 r2 = cf(10); typedef boost::result_of< functor(int&) >::type type3; // the argument is lvalue int a = 10; type3 r3 = f(a); typedef boost::result_of< functor(int const&) >::type type4; // the argument is const lvalue const int ca = 10; type4 r4 = f(ca); </quote> You can find the complete page tere: http://svn.boost.org/svn/boost/trunk/libs/utility/utility.htm If noone objects I will merge it to release branch in a few days.