On 8/26/2011 2:08 PM, John Maddock wrote:
Is there anything obvious I'm doing wrong here? I'm using VC10 BTW, and big_number inherits from proto::terminal<big_number*> in case that makes any difference.
That last bit does make a difference. Proto grammar matching keys off the underlying proto expression type. So change this:
proto::terminal<boost::math::big_number<proto::_> >
to this:
proto::terminal<big_number*>
I assume you mean
proto::terminal<big_number<proto::_>*>
but I still get get the same error messages (the same with all the variations of the above I tried).
There's a confusion here. I was basing my suggestion on your statement: "big_number inherits from proto::terminal<big_number*>" But you misspoke, so my suggestion was wrong.
(Not sure exactly what you mean by "big_number inherits from proto::terminal<big_number*>. You clearly don't mean that. You mean either i/ big_number extends proto::terminal<big_number*>::type or ii/ big_number inherits from proto::terminal<big_number*>::type. Either way, the answer is the same.)
Ah yes, I meant proto::terminal<big_number<arg>*>::type.
Ah.
Also changed the grammar to use the proto::switch_, and yes that is better, well a bit anyway ;-)
The following is not a valid Proto grammar: proto::terminal<big_number<proto::_>*> At least, it won't match what you think it matches. Proto grammars are fairly limited in what pattern matching they do. You can see the horrible details at: http://www.boost.org/doc/libs/1_47_0/doc/html/boost/proto/matches.html Of relevance here is is the part that describes /lambda-matches/, which describes how terminals are matched. The pattern matching recurses into templates, but it doesn't peel off pointers and references and such (although it could). In this case, I would define a separate is_big_number trait like: template<typename T> struct is_big_number_ptr : mpl::false_ {}; template<typename Arg> struct is_big_number_ptr<big_number<Arg>*> : mpl::true_ {}; and use the trick with proto::and_ and proto::if_ that I gave you before. HTH, -- Eric Niebler BoostPro Computing http://www.boostpro.com