C++ Concept Example

concept.cpp

template<typename T, typename=void>
struct has_release : std::false_type {};

template<typename T>
struct has_release<T, decltype(std::declval<T>().Release())> : std::true_type {};

template<typename T>
class Wrapper {
  T mData;
  
public:
 ~Wrapper() {
   if constexpr(has_release<T>::value) { mData.Release(); }
 }
};

// C++20 Templates - the Next Level: Concepts and More - Andreas Fertig [ ACCU 2021 ]
// https://www.youtube.com/watch?v=ZGPz4hoBPck

// https://andreasfertig.info/

concept_2.cpp

#include <type_traits>
#include <concepts>
#include <iostream>

template <typename T>
constexpr bool critical_code_v() { return false;};

struct critical_code_semantics_tag {};
template <typename T> requires std::is_base_of_v<critical_code_semantics_tag,T>
constexpr bool critical_code_v() { return true;};

template<typename T>
concept critical_code = critical_code_v<T>();

template<typename T>
struct mark_critical : public T, public critical_code_semantics_tag {
    using T::operator();
};
//deduction guide
template<typename T> mark_critical(T) -> mark_critical<T>;

template<critical_code Alert>
void run_with_priviliges(const std::string& msg, Alert alert) {
    alert(msg);
}

int main() {
    run_with_priviliges("hello world", mark_critical{[](const auto& msg) { std::cout << msg << std::endl;}});
    return 0;
}