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

user_1547699 0
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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..)

c++17 variant c++
2 Answers

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)>;
user_8176430

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
user_1061040
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