Re: [Boost-users] [mpl] Is it possible to mpl_assert dependingonthe derivation of a class

From: Hughes, James (jhughes_at_[hidden])
Date: 2007-08-21 10:37:34

> -----Original Message-----
> From: boost-users-bounces_at_[hidden] 
> [mailto:boost-users-bounces_at_[hidden]] On Behalf Of Martin Apel
> Sent: 21 August 2007 15:00
> To: boost-users_at_[hidden]
> Subject: Re: [Boost-users] [mpl] Is it possible to mpl_assert 
> dependingonthe derivation of a class
> 
> Hughes, James wrote:
> >
> >     Just a quick addendum to this. I tried out a combination of the
> >     two - using a BOOST_STATIC_ASSERT((boost::is_base_of<Base, T>
> >     >::value)) inside the do_it function described above, and found
> >     what I thought was odd behaviour with is_base_of.
> >
> >     The following excerpt shows the behaviour
> >
> >     class A {};
> >
> >     class B : public A {};
> >
> >     typedef A C;
> >
> >      BOOST_STATIC_ASSERT((boost::is_base_of<A,B> >::value)) 
>    // this
> >     passes
> >
> >      BOOST_STATIC_ASSERT((boost::is_base_of<A,C> >::value)) 
>    // this
> >     fails
> >
> >     I would expect both to pass, as is_base_of should 
> return true when
> >     both parameters are the same, and I thought that 
> typedef did make
> >     classes the same/equivalent
> >
> >     
> > 
> http://www.boost.org/doc/html/boost_typetraits/reference.html#boost_ty
> > petraits.is_base_of
> >
> >     Is there something I am missing about typedef? Or is
> >     boost::is_base_of unable to handles the aliasing?
> >
> >     James
> >
> >      
> >
> Hi James,
> 
> I tried this with GCC 4.2 and 3.4.6 under Linux. It passes 
> for both cases. So it might be your compiler, which is doing 
> something wrong.
> 
> Martin
> 
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> 
> 

I'm using gcc 3.4.3 (Cross compiler to Arm). I had a thought it might be
down to having some pure virtual functions in A, which meant that my
typedef resulting in an incomplete type, but I removed those as a test
and still got the same error. But that wouldn't explain why changing
from a typedef to a derivation fixed the problem.

Using boost 1.33.1 btw.

I'll assume it's the compiler for now!!

James

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