On 6/11/2010 1:57 AM, Joel Falcou wrote:
Eric Niebler wrote:
Just curious, what does your custom generator do?
Given a proto expression X, it builds a table_expr< typename proto::tag_of<X>::type, X>
basically I add the tag of the expression in the expression wrapper type. Sounds silly but later, we need to know if a given expression is of tag A or B and doing so cut a lot of compile time compared to calling tag_of each time.
You could access the nested proto_tag typedef directly instead of going through tag_of (e.g. typename X::proto_tag). Compile-time matters to me too, which is why I have (so far) avoided allowing arbitrary types declare themselves Proto expressions. Once you do that, you start forcing the extensive use of these trait metafunctions, and I worry about what it might do to compile times.
It also allow us to overload table_expr behavior based on tag without relying on the internal type of proto expression, making it easy for developper to add such special behavior on some non-trivial expression node.
OK. Interesting, thanks. -- Eric Niebler BoostPro Computing http://www.boostpro.com