Re: [Boost-users] Type List Iteration?

--- At Wed, 5 Oct 2005 09:50:54 -0400, David Abrahams wrote:

Aleksey Gurtovoy writes:

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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 , 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. 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'm pretty sure I've needed something like that before... Oh yeah, the FSM example could probably benefit from it! A lot!

Thanks for this solution Aleksey! This works great. I also used your suggestion to throw an exception to unwind when the right type was found. (Throwing an exception is not my favorite solution, but functional.) David, I'm only working with the boost documentation; I don't have the book, so I could not understand your suggestion using fold<>. It didn't seem to match the template. typedef fold::type t; I further didn't understand the NextFunctionType argument. Maybe the book would make this more clear. :-) Not having documentation for for_each makes it difficult to use. ;-) All of the documentation that I found, talks about meta-functions. for_each () seems to be a real function. This is quite useful to understand. What other real functions are undocumented? Thanks again for the help and the education! ...Duane