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.

Given V as decltype(std::forward_like<Self>(std::declval<variant>())), these overloads are equivalent to forwarding to the non-member std::visit overload set:

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

# Return value

The result of the corresponding std::visit invocation.
Nothing if R is cv-qualified void; otherwise, the result of the corresponding std::visit<R> invocation.

# Exceptions

Only throws if the underlying 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 <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::cout << "int = " << i << '\n'; },
        [](std::string_view s){ std::cout << "string = \"" << s << "\"\n"; },
        [](const Base&){ std::cout << "base\n"; }
    };
 
    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