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Re: Virtual functions in constructors. Is it possible?

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Werner ha scritto:
> On Jul 2, 11:25 am, Anonymous <anonym...@no.net> wrote:
> 
> 
>> no, because init() is called from a destructor of an object passed as
>> argument to the constructor. From top down, if init() throws an
>> exception, then the destruction fails, then the construction fails..
> 
> Init() may not fail by throwing, since it's called from a
> destructor, and throwing would imply terminating (15.2.3).
> 
> Kind Regards,
> 
> Werner

Ok, after all I think that if necessary init() might handle failures 
inside its body.

class VirtualBase {
protected:
     class Initializer;
     friend class Initializer;

     class Initializer {
     public:

         Initializer() {
             std::cout << "Initializer" << std::endl;
             p = 0;
         }

         ~Initializer() {
             std::cout << "~Initializer" << std::endl;
             if (p)
                 p->Init(); // call the virtual function
         }
         // might be private if VirtualBase is declared as friend...

         void Register(VirtualBase* b) const {
             p = b;
         }
     private:
         mutable VirtualBase* p;
         // private and not implemented
         Initializer(const Initializer&);
         void operator =(const Initializer&);
     };
public:

     VirtualBase(const Initializer& i) {
         std::cout << "VirtualBase" << std::endl;
         i.Register(this);
     }
private:
     virtual void Init() = 0;
     // will be called immediately after the constructor
     // of the most derived class
};

// This is the actual hierarchy

class Base : public virtual VirtualBase {
public:

     Base(const VirtualBase::Initializer& i = Initializer()) : 
VirtualBase(i) {
         std::cout << "Base" << std::endl;
     }

     ~Base() {
         std::cout << "~Base" << std::endl;
     }

     void Init() {
         std::cout << "Base::Init()" << std::endl;
     }
};

class Derived : public Base {
public:
     //  Derived() : Base() {} // compile-time error as wanted

     Derived(const VirtualBase::Initializer& i = Initializer()) :
     Base(i), /* Base(i) is optional...*/
     VirtualBase(i)
     {
         std::cout << "Derived" << std::endl;
     }

     ~Derived() {
         std::cout << "~Derived" << std::endl;
     }

     void Init() {
         std::cout << "Derived::Init()" << std::endl;
     }
};


int main()  {
   Base x;  // calls Base::Init
   Derived y ; // calls Derived::Init
   return( 0 ) ;
}

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Virtual functions in constructors. Is it possible? Anonymous <anonymous@no.net> - 2011-07-02 00:19 +0200
  Re: Virtual functions in constructors. Is it possible? "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-07-02 00:37 +0200
    Re: Virtual functions in constructors. Is it possible? Anonymous <anonymous@no.net> - 2011-07-02 01:19 +0200
      Re: Virtual functions in constructors. Is it possible? "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-07-02 08:50 +0200
        Re: Virtual functions in constructors. Is it possible? Anonymous <anonymous@no.net> - 2011-07-02 10:50 +0200
          Re: Virtual functions in constructors. Is it possible? "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-07-02 11:17 +0200
            Re: Virtual functions in constructors. Is it possible? Anonymous <anonymous@no.net> - 2011-07-02 11:25 +0200
              Re: Virtual functions in constructors. Is it possible? Anonymous <anonymous@no.net> - 2011-07-02 11:31 +0200
              Re: Virtual functions in constructors. Is it possible? "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-07-02 12:00 +0200
              Re: Virtual functions in constructors. Is it possible? Werner <werasm@gmail.com> - 2011-07-04 01:10 -0700
                Re: Virtual functions in constructors. Is it possible? Anonymous <anonymous@no.net> - 2011-07-04 20:41 +0200
                Re: Virtual functions in constructors. Is it possible? "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-07-04 21:35 +0200
                Re: Virtual functions in constructors. Is it possible? Leo Equinox Gaspard <ekinox1995@gmail.com> - 2011-07-04 23:59 +0200
                Re: Virtual functions in constructors. Is it possible? "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-07-05 11:09 +0200
                Re: Virtual functions in constructors. Is it possible? Leo Equinox Gaspard <ekinox1995@gmail.com> - 2011-07-05 13:15 +0200
                Re: Virtual functions in constructors. Is it possible? "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-07-05 14:51 +0200
                Re: Virtual functions in constructors. Is it possible? Leo Equinox Gaspard <ekinox1995@gmail.com> - 2011-07-05 19:55 +0200
                Re: Virtual functions in constructors. Is it possible? Anonymous <anonymous@no.net> - 2011-07-05 20:46 +0200
                Re: Virtual functions in constructors. Is it possible? "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-07-05 21:23 +0200
                Re: Virtual functions in constructors. Is it possible? Werner <werasm@gmail.com> - 2011-07-06 00:14 -0700
  Re: Virtual functions in constructors. Is it possible? Virchanza <virtual@lavabit.com> - 2011-07-05 14:58 -0700
    Re: Virtual functions in constructors. Is it possible? "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-07-06 01:28 +0200

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