CODEWITHSUNDEEP
c++c++17variant
Anubis
Anubis

Reputation: 7435

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

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..)

Upvotes: 6

Views: 969

Answers (2)

Criticize SE actions means ban
Criticize SE actions means ban

Reputation: 58848

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

Upvotes: 8

StoryTeller - Unslander Monica
StoryTeller - Unslander Monica

Reputation: 170055

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)>;

Upvotes: 10

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