std::variant<Types...>::visit

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);.

Parameters

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

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.

Exceptions

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

Notes

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

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});
#else
    std::visit(overloads{use_int, use_str}, var1);
    std::visit(overloads{use_int, use_str}, var2);
#endif
}

Output:

int = 42
string = abc

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