The latest 16.6 update to Visual Studio 2019 removed std::plus::result_type
, std::minus::result_type
, and related typedefs. (They're deprecated in C++17 and removed in C++20.) A greatly simplified version of the code looks like this:
template <typename FF>
struct function_wrapper {
function_wrapper(FF func, const std::string& name) : func_(func), name_(name) { }
int operator()(int i1, int i2) const { return func_(i1, i2); }
// ... other stuff ...
FF func_;
std::string name_;
};
template <typename FF>
int use_function(const function_wrapper<FF>& func, const std::pair<int, int>& args) {
return func(args.first, args.second);
}
funcWrapper<boost::function<int(int, int)>> plus_func(std::plus<int>(), "plus");
std::cout << use_function(plus_func, std::make_pair<int, int>(1, 2)) << std::endl;
After the update, this no longer compiles, generating the error:
boost\1.72.0\boost\bind\bind.hpp(75,25): error C2039: 'result_type': is not a member of 'std::plus<int>'
I can't add a result_type
typedef back into std::plus
, so I need another way to fix this. The thing is, the resulting code needs to compile under C++03, too, so lambdas and >=C++11 constructs are not a viable option. I can re-implement std::plus
and add in the now-removed typedefs myself to make Boost happy, but is there a better way?
Wrap old functors with:
template <typename F>
struct functor;
template <template <typename> class F, typename T>
struct functor<F<T> > : F<T>
{
typedef T result_type;
typedef T first_argument_type;
typedef T second_argument_type;
};
Then:
function_wrapper<boost::function<int(int, int)> >
plus_func(functor<std::plus<int> >(), "plus");
// ~~~~~~~^ ~^~
Alternatively, you can call boost::bind
specifying the result type as a template argument:
boost::bind<int>(func, args...);
or:
boost::bind(boost::type<int>(), func, args...);