// The values bound to the placeholders Value *d[2]; <...> // The result of evaluating arithmetic expressions typedef Value& result_type;

So, you store pointers to the variants and return references, thus preventing copying. But why does the copying cause the aforementioned crash? Does it look like a bug in Proto? That's quite weird, because I never encountered any issue with variant copying... -- View this message in context: http://boost.2283326.n4.nabble.com/proto-variant-variant-crashes-proto-expre... Sent from the Boost - Dev mailing list archive at Nabble.com.