[boost] cannot get lambda::bind to work with abstract class (even with boost::ref)

From: Jaakko Jarvi (jajarvi_at_[hidden])
Date: 2003-10-24 14:12:43

This is a bug. Type struct_a ends up in a tuple type, and even though
a tuple object is never instantiated, the type is. In this type,
struct_a is used as a member variable type, which is not allowed.

For a quick fix, I'd need is_abstract_base type traits, 
(there seemst to be one proposed by rani sharoni) but it's not part of
type_traits right.

But there is a better but less quick fix too, hopefully will get fixed
with the new TR tuples and fusion.

  Jaakko

In our last exciting episode "Brock Peabody" wrote:
> Importance: Normal

> I'm sure I'm missing something simple again, but if I try to compile:

>    #include <boost/lambda/bind.hpp>

>    struct a_struct {

>       virtual void f() = 0;
>    };

>    void f(a_struct&);

>    int
>    main() {

>       a_struct* a;

>       boost::lambda::bind(&f, boost::ref(*a));  

>       return 0;
>    }

> With MSVC 7.1 I get an error message like: "c:\Program Files\Microsoft
> Visual Studio .NET 2003\Vc7\include\boost\tuple\detail\tuple_basic.hpp(354)
> : error C2259: 'a_struct' : cannot instantiate abstract class
>         due to following members:
>         'void a_struct::f(void)' : pure virtual function was not defined..."

> If I change it to use plain boost::bind instead of boost::lambda::bind it
> works.  Lambda::var doesn't do the trick either.  Interestingly, if I change
> the definition of a_struct to:

>    struct a_struct : boost::noncopyable {
>    private:

>       a_struct();
>    };

> It works with lambda::bind.  As far as I can tell you shouldn't be able to
> do anything with this version that you couldn't with the abstract base class
> version.

> Any ideas?

> Thanks!

> Brock

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Sincerely,
Jaakko Järvi