"Eric Niebler" schrieb im Newsbeitrag news:<4A8BB56F.7050706@boostpro.com>...
Steven Watanabe wrote:
christophe henry wrote:
I am trying to build a mpl::vector from an expression like
(string(),ClassA(),ClassB())
To get a mpl::vector
Is there a way to do this or I should give up the idea?
Does fold_tree help?
It does.
*snip* Ah It see. Thanks a lot, I think I got the idea. I just have a concern with: template<class T> struct is_my : mpl::false_ {}; template<> struct is_my<std::string> : mpl::true_ {}; template<> struct is_my<ClassA> : mpl::true_ {}; template<> struct is_my<ClassB> : mpl::true_ {}; As it forces extra declarations which not everybody is willing to make. But based on the same fold idea I can allow something like: attributes_ << int() << std::map<int,int>() << bool() Where attributes_ is made a proto terminal<my_tag> with proto::extends and the following grammar (which I shamelessly stole from the doc): struct BuildAttributes : proto::or_< // Don't add the flag terminal to the list proto::when< proto::terminal< my_tag > , proto::_state
// Put all other terminals at the head of the // list that we're building in the "state" parameter , proto::when< proto::terminal<proto::_> , fusion::cons<proto::_value, proto::_state>(proto::_value, proto::_state)
// For left-shift operations, first fold the right // child to a list using the current state. Use // the result as the state parameter when folding // the left child to a list. , proto::when< proto::shift_left<BuildAttributes, BuildAttributes> , proto::fold< proto::_ , fusion::nil() , BuildAttributes>()
{}; I then just have to invert the order again as it gets reversed (ok a few seconds more to compile...): boost::mpl::copy<typename boost::result_of<BuildAttributes(Attr)>::type,boost::mpl::front_inserter<boost::mpl::vector<> > >::type Correct? Thanks a lot, Christophe _________________________________________________________________ Drag n’ drop—Get easy photo sharing with Windows Live™ Photos. http://www.microsoft.com/windows/windowslive/products/photos.aspx