cpp check member exist

check_if_member_exist.cpp

// should read
// https://hedzr.com/c++/algorithm/cxx-is_detected-and-detection-idioms

#include <iostream>
#include <type_traits>
#include <experimental/type_traits>
// AClass definition
class AClass {
public:
    std::string dueDate;
    std::string title;

    void setDueDate(const std::string& date) {
        dueDate = date;
    }
};

// BClass definition
class BClass {
public:
    std::string title;
};

template<typename T>
using setDueDate_t = decltype( std::declval<T&>().setDueDate("") );

template<typename T>
constexpr bool has_setDueDate = std::experimental::is_detected_v<setDueDate_t, T>;

// MetaDataSetter class
template <typename T>
class MetaDataSetter {
public:
    static void setMetaData(T& obj) {
        obj.title = "example";
        if constexpr (has_setDueDate<T>) {
            std::cout << "in" << std::endl;
            obj.setDueDate("example date ehere!");
        } else {
            std::cout << "out" << std::endl;

        }
    }
};

int main() {
    AClass aObj;
    BClass bObj;

    MetaDataSetter<AClass>::setMetaData(aObj);
    MetaDataSetter<BClass>::setMetaData(bObj);

    std::cout << "AClass: " << aObj.title << ", " << aObj.dueDate << std::endl;
    std::cout << "BClass: " << bObj.title << std::endl;

    return 0;
}