std::variant<Types...>::visit
From cppreference.com
|
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> ( ) ) )
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>
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
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
See also
|
(C++17)
|
calls the provided functor with the arguments held by one or more variants (function template) |