When using just pointers/references to std::variant<T…> defined from T… where some of T is only forward declared – I have this problem that I cannot even use pointers nor references to this std::variant – because its bases classes wanted to be instantiated – and they require std::is_default_constructible and other traits. See example code: #include <variant>… Read More Is required for class templates to be instantiated to use only pointer or reference to them?

I’m trying to turn a vector of variants into a tuple of vectors variadicly (i.e. I’d like to factor out the following code into a variadic template std::variant<Ts…>). std::vector<std::variant<float, int>> vector_of_variants; vector_of_variants.emplace_back(1); vector_of_variants.emplace_back(2.f); std::tuple<std::vector<float>, std::vector<int>> result; for (auto& el : vector_of_variants) { auto index = el.index(); std::get<index>(result).pushback(std::get<index>(el)); // error: index is runtime value } However,… Read More runtime indexing with std::get

I have two variant objects of the following type struct FigureMove {}; struct PieceMove {}; using Move = std::variant<FigureMove, PieceMove>; I want to supply two Move objects to a function and call different functions depending on the underlying types in the variants. I have two different versions of the function which takes the Move objects.… Read More Difference in supplying two variant objects separately vs in an array

I have been struggling a bit to get my code using std::variant in combination with std::visit to work. I have now reduced my code to a minimum of just using one type in my variant and still the compiler complains about no matching call to visit. #include <iostream> #include <variant> #include <vector> #include <array> class… Read More Correct use of std::variant and std::visit when functor requires multiple arguments

In C++ we have std::variant for creating a sum-types. For example, the following will allow v to hold either a std::string or an int: #include <variant> #include <string> //… std::variant< std::string, int> v; v = "aaa"; // now v holds a std::string v = 5; // now v holds an int In addition – the… Read More C# Equivalent for C++ std::variant (sum type)

Consider the following: class Foo { […] public: Foo(int); } class Bar { […] public: Bar(int); } using MyVariant = std::variant<Foo,Bar>; How can one direct initialize (i.e no copy and no Foo building involved) an instance of MyVariant as a Bar ? >Solution : Pass the a tag of type std::in_place_type_t<Bar> as first constructor parameter:… Read More How to direct initialize a C++ variant with one of its non-default option?

I am trying to make range(cells(1,1), cells(10,1) to have value in Range AAA and when value is empty in AAA, it shows value in Range BBB. But the result what I got is only have Range BBB in given range. For example: When AAA(1) = 12345, Cells(1,1) = 12345 When AAA(2) = empty, Cells(2,1) =… Read More when value of Variant is empty assign value in another Variant

I have two vectors: A vector of a type that acts as a union, whose type I can retrieve. The other vector is a vector of variants of another type. I want to use std::transform to do a conversion to one of my variant types. However, I receive a compile error that std::transform or rather… Read More std::transform with variant