Re: [Boost-users] Determine Parent Class from boost::any

Subject: Re: [Boost-users] Determine Parent Class from boost::any
From: Ovanes Markarian (om_boost_at_[hidden])
Date: 2009-11-23 11:58:35

Hi!
what do you mean by parent? boost::any does not derive from any other class.
Just a note, using that version of cast:

       boost::any_cast<a*>(&any);
or
       boost::any_cast<a const*>(&any);

will not throw, but return a null pointer if any does not contain the
expected type. Consider using boost::variant, which supports visitor-pattern
for dispatching.

Best Regards,
Ovanes

On Mon, Nov 23, 2009 at 5:18 PM, Yan Cheng Cheok <yccheok_at_[hidden]> wrote:

>
> May I know is there any way to determine parent class from boost::any?
>
> #include <iostream>
> #include <boost/any.hpp>
>
> class a {
> public:
>    virtual ~a() {}
> };
>
> class b : public a {
> };
>
> bool is_class_a(const boost::any& any)
> {
>    return boost::any_cast<a>(&any) != 0;
> }
>
> bool is_class_a_v2(const boost::any& any)
> {
>    try
>    {
>        boost::any_cast<a>(any);
>        return true;
>    }
>    catch(const boost::bad_any_cast &)
>    {
>        return false;
>    }
> }
>
> int main()
> {
>    std::cout<< is_class_a(b())<< std::endl;    // return 0. but i wish to
> return 1.
>    std::cout<< is_class_a(a())<< std::endl;    // return 1.
>
>    std::cout<< is_class_a_v2(b())<< std::endl; // return 0. but i wish to
> return 1.
>    std::cout<< is_class_a_v2(a())<< std::endl; // return 1.
> }
>
>
>
>
>
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