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Showing content from https://en.cppreference.com/w/cpp/language/../algorithm/../utility/variant/visit.html below:

std::variant<Types...>::visit - cppreference.com

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 [edit] 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
}

Output:

int = 42
string = “abc”
base
[edit] See also calls the provided functor with the arguments held by one or more variants
(function template) [edit]

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