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* RE: Non-default ctors, virtual base classes, & multiple inheritance all at  once!
@ 2000-09-06 10:13 Jan Reimers
  2000-09-06 11:15 ` Non-default ctors, virtual base classes, & multiple inheritan ce " sidster
  0 siblings, 1 reply; 8+ messages in thread
From: Jan Reimers @ 2000-09-06 10:13 UTC (permalink / raw)
  To: 'sidster'
  Cc: 'gcc@gcc.gnu.org', 'scherrey@switchco.com'

> -----Original Message-----
> From: sidster [ mailto:patrick@mail.boxsoft.com ]
> Sent: Wednesday, September 06, 2000 9:33 AM
> To: Alexandre Oliva
> Cc: scherrey@switchco.com; gcc@gcc.gnu.org
> Subject: Re: Non-default ctors, virtual base classes, & multiple
> inheritance all at once!
> 
> If I understand what you are suggesting correctly then it is
> _impossible_ to get the desired behavior with the given code.
> 
> Since  template <typename X> class HoldX  has no knowledge of what
> base classes  X  might have to even provide constructors to specify
> them in its "mem-initializer-list".

template <typename X> class HoldX : public virtual X
{
  HoldX(int) : A(int),X(int) {};
};

Now the template parameter X is required to derive from A, restricting the
utility of HoldX.  But most template code places requirements on the
template parameters, STL being an example.  There is nothing earth
shattering about this.  Make virtual base classes abstract with no data, and
everything will work out.

JR

^ permalink raw reply	[flat|nested] 8+ messages in thread
* Re: Non-default ctors, virtual base classes, & multiple inheritance all atonce!
@ 2000-09-05 12:12 rlau
  2000-09-05 16:35 ` Non-default ctors, virtual base classes, & multiple inheritance all at once! llewelly
  0 siblings, 1 reply; 8+ messages in thread
From: rlau @ 2000-09-05 12:12 UTC (permalink / raw)
  To: gcc

your template class do not have a corresponding constructor that accepts
(int) as argument.
Check with comp.prog.c++.moderate!

Good luck!





Benjamin Scherrey <scherrey@switchco.com>@gcc.gnu.org on 09/05/2000
12:58:20 PM

Please respond to scherrey@switchco.com

Sent by:  gcc-owner@gcc.gnu.org


To:   gcc@gcc.gnu.org
cc:
Subject:  Non-default ctors, virtual base classes, & multiple inheritance
      all at once!


    I'm having some trouble getting non-default constructors called for
virtual baseclasses in certain instances.. I've attached some code that
demonstrates this problem. In some cases, I can pass a parameter up the
tree to the virtual base class, in others, the default ctor is always
called even though my code clearly specifies the ctor taking a parm. Is
this a compiler bug or a language design issue?

    thanx & later,

        Ben Scherrey

//
//   vinherit.cpp - Tests resolution of virtual inheritance.
//

#include <iostream>
#include <string>

class A
{
public:
     A( void ) : v(0) { cout << "A ctor @ " << this << ", v = " << v <<
endl; }
     A( int a ) : v(a) { cout << "A int ctor @ " << this << ", v = " << v
<< endl; }
     A( const A& a ) : v(a.v) { cout << "A copy ctor @ " << this << " from
" << &a << ", v = " << v << endl; }
     virtual ~A( void ) { cout << "A dtor @ " << this << ", v = " << v <<
endl; }

     virtual void f1( void ) { cout << "A::f1 v = " << v << endl; }
     virtual void f2( void ) = 0;
     int v;
};

class B : public A
{
public:
     B( void ) : A() { cout << "B ctor @ " << this << endl; }
     B( int i ) : A( i ) { cout << "B int ctor @ " << this << endl; }
     B( const B& a ) : A(a) { cout << "B copy ctor @ " << this << " from "
<< &a << endl; }
     virtual ~B( void ) { cout << "B dtor @ " << this << endl; }
     virtual void f2( void ) { cout << "B::f2" << endl; }
};

class C : public virtual A
{
public:
     C( void ) : A() { cout << "C ctor @ " << this << endl; }
     C( int i ) : A(i) { cout << "C int ctor @ " << this << endl; }
     C( const C& a ) : A(a) { cout << "C copy ctor @ " << this << " from "
<< &a << endl; }
     virtual ~C( void ) { cout << "C dtor @ " << this << endl; }
     virtual void f2( void ) { cout << "C::f2" << endl; }
};

template < typename X >
class HoldX : public virtual X
{
public:
     template < typename T >
     HoldX( T t ) : X( t ) { cout << "T HoldX ctor @ " << this << endl; }
     HoldX( void ) : X() { cout << "HoldX ctor @ " << this << endl; }
     HoldX( const HoldX& a ) : X(a) { cout << "HoldX copy ctor @ " << this
<< " from " << &a << endl; }
     virtual ~HoldX( void ) { cout << "HoldX dtor @ " << this << endl; }
     virtual void f2( void ) { cout << "HoldX::f2" << endl; }
};

template < typename Y, typename X >
class HoldY : public Y, public HoldX< X >
{
public:
     template < typename T >
     HoldY( T t ) : Y( t ), HoldX< X >( t ) { cout << "T HoldY ctor @ " <<
this << endl; }
     HoldY( void ) : Y(), HoldX< X >() { cout << "HoldY ctor @ " << this
<< endl; }
     HoldY( const HoldY& a ) : Y(a), HoldX< X >(a) { cout << "HoldY copy
ctor @ " << this << " from " << &a << endl; }
     virtual ~HoldY( void ) { cout << "HoldY dtor @ " << this << endl; }
     virtual void f2( void ) { cout << "HoldY::f2" << endl; }
};

template < typename Y, typename X >
class HoldZ : public Y, virtual public HoldX< X >
{
public:
     template < typename T >
     HoldZ( T t ) : Y(t), HoldX< X >(t) { cout << "\nT HoldZ ctor @ " <<
this << endl; }
     HoldZ( void ) : Y(), HoldX< X >() { cout << "\nHoldZ ctor @ " << this
<< endl; }
     HoldZ( const HoldZ& a ) : Y(a), HoldX< X >(a) { cout << "\nHoldZ copy
ctor @ " << this << " from " << &a << endl; }
     virtual ~HoldZ( void ) { cout << "HoldZ dtor @ " << this << endl; }
     virtual void f2( void ) { cout << "HoldZ::f2" << endl; }
};

int main( void )
{
     cout << "Test case for virtual inheritance." << endl;

     cout << "\nConstructing HoldX< A > X1;" << endl;
     HoldX< A > X1;      // OK

     cout << "\nConstructing HoldX< A > X2(2);" << endl;
     HoldX< A > X2(2);   // OK

     cout << "\nConstructing HoldX< B > X3;" << endl;
     HoldX< B > X3;      // OK

     cout << "\nConstructing HoldX< B > X4(4);" << endl;
     HoldX< B > X4(4);   // OK

     cout << "\nConstructing HoldX< C > X5;" << endl;
     HoldX< C > X5;      // OK

     cout << "\nConstructing HoldX< C > X6(6);" << endl;
     HoldX< C > X6(6);   // Huh? Why no A(int) call?

     cout << "\nConstructing HoldY< B, A > Y1;" << endl;
     HoldY< B, A > Y1;   // OK

     cout << "\nConstructing HoldY< C, A > Y2;" << endl;
     HoldY< C, A > Y2;   // OK

     cout << "\nConstructing HoldY< C, A > Y3(3);" << endl;
     HoldY< C, A > Y3(3);// Huh? No A(int) again!

     cout << "\nConstructing HoldZ< B, A > Z1;" << endl;
     HoldZ< B, A > Z1;   // OK

     cout << "\nConstructing HoldZ< C, A > Z2;" << endl;
     HoldZ< C, A > Z2;   // OK

     cout << "\nConstructing HoldZ< C, A > Z3(3);" << endl;
     HoldZ< C, A > Z3(3);// Again no A(int)!
     Z3.f1();
     Z3.f2();

     cout << "\nConstructing C C1(1);" << endl;
     C C1(1);            // OK

     cout << "\nTest complete." << endl;
     return 0;
}

//
// eof( vinherit.cpp )
//




^ permalink raw reply	[flat|nested] 8+ messages in thread
* Non-default ctors, virtual base classes, & multiple inheritance all at once!
@ 2000-09-05 11:15 Benjamin Scherrey
  2000-09-06  3:27 ` Alexandre Oliva
  0 siblings, 1 reply; 8+ messages in thread
From: Benjamin Scherrey @ 2000-09-05 11:15 UTC (permalink / raw)
  To: gcc

    I'm having some trouble getting non-default constructors called for
virtual baseclasses in certain instances.. I've attached some code that
demonstrates this problem. In some cases, I can pass a parameter up the
tree to the virtual base class, in others, the default ctor is always
called even though my code clearly specifies the ctor taking a parm. Is
this a compiler bug or a language design issue?

    thanx & later,

        Ben Scherrey

^ permalink raw reply	[flat|nested] 8+ messages in thread
end of thread, other threads:[~2000-09-06 11:15 UTC | newest]

Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2000-09-06 10:13 Non-default ctors, virtual base classes, & multiple inheritance all at once! Jan Reimers
2000-09-06 11:15 ` Non-default ctors, virtual base classes, & multiple inheritan ce " sidster
  -- strict thread matches above, loose matches on Subject: below --
2000-09-05 12:12 Non-default ctors, virtual base classes, & multiple inheritance all atonce! rlau
2000-09-05 16:35 ` Non-default ctors, virtual base classes, & multiple inheritance all at once! llewelly
2000-09-05 22:59   ` Benjamin Scherrey
2000-09-05 11:15 Benjamin Scherrey
2000-09-06  3:27 ` Alexandre Oliva
2000-09-06  8:39   ` Joe Buck
2000-09-06  9:37   ` sidster

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