std::variant<Types...>::visit
|
(1) | (since C++26) |
|
(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);.
Parameters
| vis | - | a Callable that accepts every possible alternative from the variant |
| self | - | variant to pass to the visitor |
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.
Exceptions
Only throws if the 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 <variant>
// helper type for the visitor
template<class... Ts>
struct overloads : Ts... { using Ts::operator()...; };
int main()
{
std::variant<int, std::string> var1{42}, var2{"abc"};
auto use_int = [](int i){ std::cout << "int = " << i << '\n'; };
auto use_str = [](std::string s){ std::cout << "string = " << s << '\n'; };
#if (__cpp_lib_variant >= 202306L)
var1.visit(overloads{use_int, use_str});
var2.visit(overloads{use_int, use_str});
#else
std::visit(overloads{use_int, use_str}, var1);
std::visit(overloads{use_int, use_str}, var2);
#endif
}Output:
int = 42
string = abc© cppreference.com
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https://en.cppreference.com/w/cpp/utility/variant/visit2