Re: [sigc] TypeTraits

[Martin Schulze <martin-ml hippogriff de>]

Hi Arnaud!

Thanks for reporting this! You are right, the instance() method is  
completely ununsed. It was needed for some early alpha versions of  
libsigc++2 that used gcc's non-portable typeof() keyword. I never  
thought of removing it.

The problem is: formally, the type_trait<> template is part of the  
public API so I hesitate to silently remove the instance() method. On  
the hand, it doesn't really make sense to conditionally generate it -  
our only alternative.

So, I'm asking the list: is there anybody against completely removing  
the (internally unused) type_trait<>::instance() method?

Regards,

 Martin


Am 28.07.2004 18:25:51 schrieb(en) Arnaud Debaene:
> The following doesn't compile neither with VC 7.1 neither with Comeau
> (but it's ok with GCC) :
>
>
>
> class VirtualClass
>
> {
>
> public:
>
>    virtual void f()=0;
>
>
>
>    sigc::signal<void> event;
>
>    void CallbackFunc()  {};
>
>
>
>    void DoConnection()
>
>    {
>
>       event.connect(sigc::mem_fun(this, &VirtualClass:: 
> CallbackFunc));
>
>    }
>
> };
>
>
>
> This is because of the implementation of type_traits :
>
> truct type_trait
>
> {
>
>   typedef T_type  type;
>
>   typedef T_type& pass;
>
>   typedef const T_type& take;
>
>   typedef T_type* pointer;
>
>   static  T_type  instance(); /* not implemented */
>
> };
>
>
>
> When instanciating is_base_and_derived<trackable, VirtualClass>, the
> compiler refuses to generate instance() because VirtualClass is
> virtual.
> However, the instance() method is never used in the code. I do not
> know
> m4, but it seems that this method is only used with GCC to circumvent
> a
> GCC bug / use the typeof facility : see operator.h.m4, line 91.
> Therefore, I guess those type_trait::instance() methods should be
> removed, or at least generated only conditionnally.
>
>
>
> Here is the complete compiler error message with VC 7.1 :
>
>
>
>
>
> d:\users\adb\utils\libsigcplusplus\libsigc++-2.0.3\sigc++ 
> \type_traits.h(
> 33) : error C2259: 'VirtualClass' : cannot instantiate abstract class
>
>         due to following members:
>
>         'void VirtualClass::f(void)' : pure virtual function was not
> defined
>
>
> d:\users\adb\dev\temp\test_libsigcplusplus_abstractclass 
> \test_libsigcplu
> splus_abstractclass\test_libsigcplusplus_abstractclass.cpp(12) : see
> declaration of 'VirtualClass::f'
>
>
> d:\users\adb\utils\libsigcplusplus\libsigc++-2.0.3\sigc++ 
> \type_traits.h(
> 116) : see reference to class template instantiation
> 'sigc::type_trait<T_type>' being compiled
>
>         with
>
>         [
>
>             T_type=VirtualClass
>
>         ]
>
>
> d:\users\adb\utils\libsigcplusplus\libsigc++-2.0.3\sigc++\visit_each. 
> h(7
> 2) : see reference to class template instantiation
> 'sigc::is_base_and_derived<T_base,T_derived>' being compiled
>
>         with
>
>         [
>
>             T_base=sigc::trackable,
>
>             T_derived=VirtualClass
>
>         ]
>
>
> d:\users\adb\utils\libsigcplusplus\libsigc++-2.0.3\sigc++\visit_each. 
> h(1
> 13) : see reference to function template instantiation 'void
> sigc::internal::limit_derived_target<T_target,T_action>::operator
> ()<T_functor>(const T_type &) const' being compiled
>
>         with
>
>         [
>
>             T_target=sigc::trackable *,
>
>             T_action=sigc::internal::slot_do_bind,
>
>             T_functor=VirtualClass,
>
>             T_type=VirtualClass
>
>         ]
>
>
> d:\users\adb\utils\libsigcplusplus\libsigc++-2.0.3\sigc++\functors 
> \mem_f
> un.h(1798) : see reference to function template instantiation 'void
> sigc::visit_each<T_action,T_obj>(const T_action &,const T_functor &)'
> being compiled
>
>         with
>
>         [
>
>
> T_action=sigc::internal::limit_derived_target<sigc::trackable
> *,sigc::internal::slot_do_bind>,
>
>             T_obj=VirtualClass,
>
>             T_functor=VirtualClass
>
>         ]
>
>
> d:\users\adb\utils\libsigcplusplus\libsigc++-2.0.3\sigc++\adaptors 
> \adapt
> or_trait.h(267) : see reference to function template instantiation
> 'void
> sigc::visit_each<T_action,void,VirtualClass>(const T_action &,const
> sigc::bound_mem_functor0<T_return,T_obj> &)' being compiled
>
>         with
>
>         [
>
>             T_action=sig
>
> c::internal::limit_derived_target<sigc::trackable
> *,sigc::internal::slot_do_bind>,
>
>             T_return=void,
>
>             T_obj=VirtualClass
>
>         ]
>
>
> d:\users\adb\utils\libsigcplusplus\libsigc++-2.0.3\sigc++\visit_each. 
> h(1
> 24) : see reference to function template instantiation 'void
> sigc::visit_each<sigc::internal::limit_derived_target<T_target, 
> T_action>
> ,sigc::adaptor_trait<T_functor>::functor_type>(const
> sigc::internal::limit_derived_target<T_target,T_action> &,const
> sigc::adaptor_functor<T_functor> &)' being compiled
>
>         with
>
>         [
>
>             T_target=sigc::trackable *,
>
>             T_action=sigc::internal::slot_do_bind,
>
>             T_functor=sigc::bound_mem_functor0<void,VirtualClass>
>
>         ]
>
>
> d:\users\adb\utils\libsigcplusplus\libsigc++-2.0.3\sigc++\functors 
> \slot.
> h(39) : see reference to function template instantiation 'void
> sigc::visit_each_type<sigc::trackable*,sigc::internal::slot_do_bind, 
> sigc
> ::internal::typed_slot_rep<T_functor>::adaptor_type>(const T_action
> &,const sigc::adaptor_functor<T_functor> &)' being compiled
>
>         with
>
>         [
>
>             T_functor=sigc::bound_mem_functor0<void,VirtualClass>,
>
>             T_action=sigc::internal::slot_do_bind
>
>         ]
>
>
> d:\users\adb\utils\libsigcplusplus\libsigc++-2.0.3\sigc++\functors 
> \slot.
> h(37) : while compiling class-template member function
> 'sigc::internal::typed_slot_rep<T_functor>::typed_slot_rep(const
> T_functor &)'
>
>         with
>
>         [
>
>             T_functor=sigc::bound_mem_functor0<void,VirtualClass>
>
>         ]
>
>
> d:\users\adb\utils\libsigcplusplus\libsigc++-2.0.3\sigc++\functors 
> \slot.
> h(436) : see reference to class template instantiation
> 'sigc::internal::typed_slot_rep<T_functor>' being compiled
>
>         with
>
>         [
>
>             T_functor=sigc::bound_mem_functor0<void,VirtualClass>
>
>         ]
>
>
> d:\users\adb\utils\libsigcplusplus\libsigc++-2.0.3\sigc++\functors 
> \slot.
> h(1089) : see reference to function template instantiation
> 'sigc::slot0<T_return>::slot0<T_functor>(const T_functor &)' being
> compiled
>
>         with
>
>         [
>
>             T_return=void,
>
>             T_functor=sigc::bound_mem_functor0<void,VirtualClass>
>
>         ]
>
>
> d:\users\adb\dev\temp\test_libsigcplusplus_abstractclass 
> \test_libsigcplu
> splus_abstractclass\test_libsigcplusplus_abstractclass.cpp(19) : see
> reference to function template instantiation
> 'sigc::slot<T_return>::slot<sigc::bound_mem_functor0<T_return,T_obj>> 
> (co
> nst T_functor &)' being compiled
>
>         with
>
>         [
>
>             T_return=void,
>
>             T_obj=VirtualClass,
>
>             T_functor=sigc::bound_mem_functor0<void,VirtualClass>
>
>         ]
>
>
>
>
>
> Arnaud
>
>
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