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

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.

# Declarations

template< class Self, class Visitor >
constexpr decltype(auto) visit( this Self&& self, Visitor&& vis );

(since C++26)

template< class R, class Self, class Visitor >
constexpr R visit( this Self&& self, Visitor&& vis );

(since C++26)

# Parameters

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

# Notes

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

# Example

#include <print>
#include <string>
#include <string_view>
#include <variant>
 
struct Base {};
struct Derived : Base {};
 
// helper type for the visitor
template<class... Ts>
struct overloads : Ts... { using Ts::operator()...; };
 
// the variant to visit
using var_t = std::variant<int, std::string, Derived>;
 
int main()
{
    const auto visitor = overloads
    {
        [](int i){ std::print("int = {}\n", i); },
        [](std::string_view s){ std::println("string = “{}”", s); },
        [](const Base&){ std::println("base"); }
    };
 
    const var_t var1 = 42, var2 = "abc", var3 = Derived();
 
#if (__cpp_lib_variant >= 202306L)
    var1.visit(visitor);
    var2.visit(visitor);
    var3.visit(visitor);
#else
    std::visit(visitor, var1);
    std::visit(visitor, var2);
    std::visit(visitor, var3);
#endif
}

# See also

visit