< cpp‎ | utility‎ | variant
Utilities library
Language support
Type support (basic types, RTTI)
Library feature-test macros (C++20)
Dynamic memory management
Program utilities
Coroutine support (C++20)
Variadic functions
Debugging support
Three-way comparison
General utilities
Date and time
Function objects
Formatting library (C++20)
Relational operators (deprecated in C++20)
Integer comparison functions
Swap and type operations
Common vocabulary types
Elementary string conversions

template< class Self, class Visitor >
constexpr decltype(auto) visit( this Self&& self, Visitor&& vis );
(1) (since C++26)
template< class R, class Self, class Visitor >
constexpr R visit( this Self&& self, Visitor&& vis );
(2) (since C++26)

Applies the visitor vis (a Callable that can be called with any combination of types from the variant) to the variant held by self.

Given type V as decltype(std::forward_like<Self>(std::declval<variant>())), the equivalent call is:

1) return std::visit(std::forward<Visitor>(vis), (V) self);.
2) return std::visit<R>(std::forward<Visitor>(vis), (V) self);.


[edit] Parameters

vis - a Callable that accepts every possible alternative from the variant
self - variant to pass to the visitor

[edit] Return value

1) The result of the std::visit invocation.
2) Nothing if R is (possibly cv-qualified) void; otherwise the result of the std::visit<R> invocation.

[edit] Exceptions

Only throws if the call to std::visit throws.

[edit] Notes

Feature-test macro Value Std Feature
__cpp_lib_variant 202306L (C++26) member visit

[edit] Example

#include <iostream>
#include <string>
#include <variant>
// helper type for the visitor
template<class... Ts>
struct overloads : Ts... { using Ts::operator()...; };
int main()
    std::variant<int, std::string> var1{42}, var2{"abc"};
    auto use_int = [](int i){ std::cout << "int = " << i << '\n'; };
    auto use_str = [](std::string s){ std::cout << "string = " << s << '\n'; };
#if (__cpp_lib_variant >= 202306L)
    var1.visit(overloads{use_int, use_str});
    var2.visit(overloads{use_int, use_str});
    std::visit(overloads{use_int, use_str}, var1);
    std::visit(overloads{use_int, use_str}, var2);


int = 42
string = abc