The following code example is taken from the book
C++17 - The Complete Guide
by Nicolai M. Josuttis,
Leanpub, 2017
The code is licensed under a
Creative Commons Attribution 4.0 International License.
// raw code
#include "customer2.hpp"
#include <utility> // for tuple-like API
// provide a tuple-like API for class Customer for structured bindings:
template<>
struct std::tuple_size<Customer> {
static constexpr int value = 3; // we have 3 attributes
};
template<>
struct std::tuple_element<2, Customer> {
using type = long; // last attribute is a long
};
template<std::size_t Idx>
struct std::tuple_element<Idx, Customer> {
using type = std::string; // the other attributes are strings
};
// define specific getters:
template<std::size_t I> decltype(auto) get(Customer& c) {
static_assert(I < 3);
if constexpr (I == 0) {
return c.firstname();
}
else if constexpr (I == 1) {
return c.lastname();
}
else { // I == 2
return c.value();
}
}
template<std::size_t I> decltype(auto) get(const Customer& c) {
static_assert(I < 3);
if constexpr (I == 0) {
return c.firstname();
}
else if constexpr (I == 1) {
return c.lastname();
}
else { // I == 2
return c.value();
}
}
template<std::size_t I> decltype(auto) get(Customer&& c) {
static_assert(I < 3);
if constexpr (I == 0) {
return std::move(c.firstname());
}
else if constexpr (I == 1) {
return std::move(c.lastname());
}
else { // I == 2
return c.value();
}
}