Get type of a std::variant member at a given index during compile time

Question

I have defined the following variant:

std::variant<int, bool, MyType, int> myVar;

The type of the member at index 2 is MyType. How to get this during compile time? (so that I can use it in a constexpr context etc..)

Debacle

Answer 1

Use std::variant_alternative

Provides compile-time indexed access to the types of the alternatives of the possibly cv-qualified variant, combining cv-qualifications of the variant (if any) with the cv-qualifications of the alternative.

using T = std::variant_alternative_t<2, decltype(myVar)>;

Yahoo

Answer 2

Since C++17, you can use std::variant_alternative_t

std::variant_alternative_t<0, std::variant<int, std::string>> i; // int
std::variant_alternative_t<1, std::variant<int, std::string>> s; // string

Allo

Thanks for the answer. Shouldn't we swap the template typenames. i.e. index goes first ? – Debacle

@Sumudu yup. fixed – Allo