Re: [Boost-users] [lambda] typeid & abstract base class

From: Jaakko Järvi (jarvi_at_[hidden])
Date: 2006-02-17 09:41:31

On Feb 17, 2006, at 8:09 AM, Roman Krylov wrote:

> Hi all.
> I want to make function comparing two typeid's 'const T&'s , but in
> context I have only two T* pointers.
> T is abstract class having pure virtual functions.
> typeid operator takes reference, not pointer.
> If I use * operator on placeholder (ll_typeid(*_1)==ll_typeid(*_2)) -
> compiler complains that it could not instantiate T somewhere in some
> complex template.

This is a known nasty bug in lambda, that arises with abstract base  
classes, and
I haven't fixed it. It is fixable but not quickly.

   Best, Jaakko

> I also tried to use ll_static_cast in expression, but it didn't help.
> I don't attach those error messages, but anyway why should T be
> instantiated to construct L-expression with *(T*)?
> By the way I made simple functor and it works the way I want, but  
> it's 6
> lines long instead of one in_place expr. :
>>     template<typename T>
>>     struct compareRefsByTypeID
>>     {
>>     bool operator()(const T* t1, const T* t2)
>>         { return typeid((const T&)(*t1))==typeid((const T&)(*t2)); }
>>     };
> regards,
>     Roman.
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