I have a C++ 17 std::variant
. How can I reduce it to a single instance of one type using lambdas?
I am looking for something like this:
std::variant<int, std::string> v = getIntOrString();
std::string x = reduce(
v,
[](int i) {
return "It's an int: " + std::to_string(i);
},
[](std::string i) {
return "It's a string: " + i;
});
Building on the example at cppreference, you'd use std::visit
:
#include <variant>
#include <string>
#include <iostream>
template<class... Ts> struct overloaded : Ts... { using Ts::operator()...; };
template<class... Ts> overloaded(Ts...) -> overloaded<Ts...>;
int main() {
using v_type = std::variant<int, std::string>;
v_type v1{1}, v2{"2"};
auto v_to_str = overloaded{
[](int i) { return std::to_string(i) + " was an int"; },
[](std::string const& s) { return s + " was already a string"; }
};
std::cout << std::visit(v_to_str, v1) << '\n'
<< std::visit(v_to_str, v2);
}