struct A
{
   //~A() {}
};

int main()
{
   A* a = new A[10];
   delete a;    //  heap corruption when the user destructor is defined

   int *b = new int[100];
   delete b;    //  no heap corruption
};

struct NonTrivialDestructor {
   std::string s;
};
struct NotTrivialEither : NonTrivialDestructor {};

v
 +------+---+---+---+--
 | size | T | T | T |...
 +------+---+---+---+--
        ^

pseudo-delete[](T * p) {
   size_t *size = reinterpret_cast<size_t*>(p)-1;
   for (size_t i = 0; i < *size; ++i)
      (p+i)->~T();
   deallocate(size);
}

v
 +---+---+---+--
 | T | T | T |...
 +---+---+---+--
 ^