Hi
did anybody use so far destroying delete in CRTP base class templates
for correctly deleting via base pointer in C++20?
See my example:

https://godbolt.org/z/PWPxYdj5q


==========
#include <iostream>
#include <memory>
#include <type_traits>
template<typename TAG, typename destroyer_t>
constexpr
TAG *destroyer_cast(destroyer_t*ptr){
  static_assert(std::is_base_of_v<destroyer_t,TAG>);
  return static_cast<TAG*>(ptr);
}
template<typename derived>
struct base {
    ~base() { std::cout << "base dtor \n";}
    // simulate mix-in function:
    friend void print(derived const& d){
        std::cout << typeid(decltype(d)).name()<<'\n';

    }
    // only available in C++20
#ifdef __cpp_impl_destroying_delete
void operator delete( base* ptr, std::destroying_delete_t )
{
    // cannot check if TAG is subtype here directly,
    // because derived might be incomplete
    // therefore indirect the static_cast
    destroyer_cast<derived>(ptr)->~derived();
    ::operator delete((void*)ptr);
}
#endif
};

struct d: base<d> {
    using base = base<d>;
    ~d() { std::cout << "derived dtor\n";}
};


int main(){
auto p = std::make_unique<d>();
print(*p);
std::unique_ptr<d::base> pb {std::move(p)};
}
========

-- 
Peter Sommerlad
Better Software: Consulting, Training, Reviews
Modern, Safe & Agile C++
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