std::variant<Types...>::visit - cppreference.com (original) (raw)
| 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:
return std::visit(std::forward<Visitor>(vis), (V) self);.
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
The result of the std::visit invocation.
Nothing if
Ris (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
#include #include #include #include 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); }, 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] | | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |