How to use move constructor with deleted default consturctor

I have an existing piece of code like this:

struct Base {      Base() = default;  };    struct Derive: public Base  {      Derive() = default;      Derive(const Derive&) = delete;      Derive(Derive&& p) { *this = std::move(p); }      Derive& operator = (const Derive& p) = delete;      Derive& operator = (Derive&& p) {          return *this;      }  };    int main() {    Derive p;  }  

It compiles and works. Now I want to change class definition a little bit so that Base or Derived class is always constructed with certain integer parameter and never constructed without such param.

So if I try the following changes:

struct Base {      Base() = delete;      Base(int a_) : a{a_} {};  private:    int a; //new mandatory param;  };    struct Derive: public Base  {      Derive() = delete;      Derive(int a_) : Base(a_) {};      Derive(const Derive&) = delete;      Derive(Derive&& p) { *this = std::move(p); }      Derive& operator = (const Derive& p) = delete;      Derive& operator = (Derive&& p) {          return *this;      }  };    int main() {    Derive p{1};  }  

I get the compilation error

main.cpp:15:2: error: call to deleted constructor of 'Base'          Derive(Derive&& p) { *this = std::move(p); }          ^  main.cpp:4:2: note: 'Base' has been explicitly marked deleted here          Base() = delete;          ^  1 error generated.  

Apparently this way doesn't work. So how do I modify the code so it compiles and no param constructor is never called without error?

https://stackoverflow.com/questions/65571811/how-to-use-move-constructor-with-deleted-default-consturctor January 05, 2021 at 08:49AM