std::variant<Types...>::visit
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std::variant
variant::visit
(C++26)
template< class Self, class Visitor >
constexpr decltype(auto) visit( this Self&& self, Visitor&& vis );
(1)
(since C++26)
constexpr decltype(auto) visit( this Self&& self, Visitor&& vis );
template< class R, class Self, class Visitor >
constexpr R visit( this Self&& self, Visitor&& vis );
(2)
(since C++26)
constexpr R visit( this Self&& self, Visitor&& vis );
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
Run this code
#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