Re: [Boost-users] [Boost.TypeTraits] Adding specialisations

From: Kirit Sælensminde (kirit.saelensminde_at_[hidden])
Date: 2007-10-01 11:38:48

John Maddock wrote:
> Kirit Sælensminde wrote:
>> I'm wondering if finding the need to add specialisations of
>> boost::detail::function_traits_helper is a result of missing headers,
>> incorrect usage or just things that have not been added to
>> Boost.TypeTraits on purpose?
> 
> Not added on purpose: function_traits works for *function types*, and not 
> *pointer to function types*.
> 
> So:
> 
> functions_traits<int(double)>  OK.
> function_traits<int(*)(double)> bad: argument not a function type.
> 
> You can always use remove_pointer to strip a function-pointer down to a 
> function type.
> 
> HTH, John. 

That makes perfect sense, unfortunately it doesn't help.

 From the worker thread example I've removed the specialisation for 
R(**)(void) - I can't work out why there is a double indirection there, 
but it might well be contributing to the problem.

I've also changed the functor that does the type handling to this:

template< typename F >
boost::shared_ptr< Future< typename boost::function_traits< F 
 >::result_type > > operator()( F f ) {
     return run< typename boost::function_traits< typename 
boost::remove_pointer< F >::type >::result_type >( f );
}

And even to this:

template< typename F >
boost::shared_ptr< Future< typename boost::function_traits< F 
 >::result_type > > operator()( F f ) {
     return run< typename boost::function_traits< typename 
boost::remove_pointer< typename boost::remove_pointer< F >::type >::type 
 >::result_type >( f );
}

I get exactly the same error in either case:

1>e:\dev\trunk\clients\kirit saelensminde\samples\boost cookbook\worker 
thread\worker thread.cpp(112) : warning C4355: 'this' : used in base 
member initializer list
1>e:\dev\boost\install\basic\include\boost-1_34\boost\type_traits\function_traits.hpp(170) 
: error C2504: 'boost::detail::function_traits_helper<Function>' : base 
class undefined
1>        with
1>        [
1>            Function=int (__cdecl **)(void)
1>        ]
1>        e:\dev\trunk\clients\kirit saelensminde\samples\boost 
cookbook\worker thread\worker thread.cpp(209) : see reference to class 
template instantiation 'boost::function_traits<Function>' being compiled
1>        with
1>        [
1>            Function=int (__cdecl *)(void)
1>        ]
1>e:\dev\trunk\clients\kirit saelensminde\samples\boost cookbook\worker 
thread\worker thread.cpp(209) : error C2893: Failed to specialize 
function template 
'boost::shared_ptr<Worker::Future<boost::function_traits<Function>::result_type>> 
Worker::operator ()(F)'
1>        With the following template arguments:
1>        'int (__cdecl *)(void)'

Is this a dependant type problem stopping the remove_pointer from working?

K