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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 visitorvis (aCallable that can be called with any combination of types from the variant) to the variant held byself.
Given typeV asdecltype(std::forward_like<Self>(std::declval<variant>())), the equivalent call is:
Contents |
| vis | - | aCallable that accepts every possible alternative from the variant |
| self | - | variant to pass to the visitor |
R is (possibly cv-qualified)void; otherwise the result of thestd::visit<R> invocation.Only throws if the call tostd::visit throws.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_variant | 202306L | (C++26) | membervisit |
#include <print>#include <string>#include <string_view>#include <variant> struct Base{};struct Derived: Base{}; // helper type for the visitortemplate<class...Ts>struct overloads: Ts...{using Ts::operator()...;}; // the variant to visitusing var_t=std::variant<int,std::string, Derived>; int main(){constauto 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 = 42string = “abc”base
(C++17) | calls the provided functor with the arguments held by one or morevariants(function template)[edit] |
