Re: [Boost-users] Type List Iteration?

From: Aleksey Gurtovoy (agurtovoy_at_[hidden])
Date: 2005-10-05 17:46:19

David Abrahams writes:
> Aleksey Gurtovoy <agurtovoy_at_[hidden]> writes:
>
>>> I think you can see why I'd like a type list iterator solution to this. 
>>
>> Try this:
>>
>>     struct do_something
>>     {
>>         do_something( BASE* base ) : m_base( base ) {}
>>
>>         template< typename T > void operator()( mpl::identity<T> ) const
>>         {
>>             if ( T* x = dynamic_cast< T* >( this->m_base ) )
>>                 some_function( x );
>>         }
>>
>>         BASE* m_base;
>>     };
>>
>>     mpl::for_each< 
>>           mpl::vector<A,B,C>
>>         , mpl::make_identity<_1>
>>         >( do_something( base ) );
>>
>
> In this case you test for all the derived types, even if you match the
> first one, so it's not identical.

Yes, I should have mentioned it. You can always throw an exception
after finding the match, but...

> It would probably be nice of us to
> create a for_each_if() or until() function that stops when the
> function object returns true. 

... I agree.

-- 
Aleksey Gurtovoy
MetaCommunications Engineering