Advertisements I’m used to using x macros to have powerful code generation. One of the features I like specifically is that I can’t mess up the order of the values nor can I forget one. I want to know if there’s a similar strategy for arrays and function params For example: If a library provides… Read More Expand constexpr array into positional function arguments

Advertisements I’ve recently gotten back into C++ after many years in C# and java land, and am loving where C++ has gone in my absence (since pre C++11, am now soaking up C++20!). The power of templates is really exciting to me. However, I quickly ran into something that seems impossible to deal with. I’ve… Read More How to handle template class static members and storage in situations where leaving to static cleanup isn't desired

Advertisements I’m not sure what I want to achieve is possible, but I need my templated function (my_func) to be able to take both variable arguments as well as a tuple argument. Clearer description is in the code comments. struct A{ static void call_func(int a, std::string b) { std::cout<<"int is: "<<a<<", string is: "<<b<<"\n"; }… Read More Convert tuple to variadic arguments

Advertisements How can I sum all the std::size_t parameters passed through the template into one std::size_t value that will define the size of the array. template<typename T, std::size_t… N> class Example { std::array<T, N + …> data; // std::array<T, sum of all N…> }; >Solution : You almost have it. You need to use a… Read More C++ Sum parameter pack into a template argument

Advertisements I have this code with error: template <typename T1> struct A { template <typename T2> struct B { using type = char /* actually some class depending on T1 and T2 */; }; template <typename T2> using type = B<T2>; }; template <template <typename> class TT> struct C { template <typename T> using type… Read More How to use template template as template argument properly?

Advertisements I try to write a template function to initialize given systems and run the app and at the end run shutdown function on initialized systems. This code should work in my eye and intellisense doesn’t give any error but compiler: 1>C:\VisualStudio\DirectApp\AppMain.cpp(32,2): error C2668: ‘initialize_these’: ambiguous call to overloaded function 1>C:\VisualStudio\DirectApp\AppMain.cpp(28,13): message : could be… Read More variadic template 'ambiguous call to overloaded function' seems a false error

Advertisements I’m working on a templated class, and given an incoming type T the template needs to map to a "safe" const reference. (This is essentially to avoid handing the ability to mutate to a wrapped function when it’s called; see here for the real code). The original author wrote something equivalent to this: template… Read More Why is the const lost in an expression like `const T&` where T is an rvalue reference?

Advertisements I’m trying to develop a wrapper to help people use pthread on calling any member function. template <typename> struct signature; template <typename C, typename R, typename… Args> struct signature<R (C::*)(Args…)> { using return_type = R; using pure_argument_type = std::tuple<C*, std::tuple<Args…>>; // obj, {args…} using argument_type = std::tuple<R (C::*)(Args…), pure_argument_type>; // obj.mem_fn, {obj, args…} };… Read More Why can't I std::apply for a member function

Advertisements I use std::experimental::is_detected to determine if class has certain member functions: #include <utility> #include <experimental/type_traits> template<typename USC> class Descriptor { private: template<class T> using has_member1_t = decltype(std::declval<T>().member1(std::declval<std::vector<char> &>())); public: static constexpr bool has_member1 = std::experimental::is_detected_convertible_v<long long, has_member1_t, USC>; }; The problem is I also need to determine if class has certain template member function… Read More Can you detect template member of a class using std::is_detected