Maurizio Vitale wrote:
Eric, the attached file exibits a problem with (I think) display_expr: The second line in main() fails. But if you comment out the definition of META_EXPR(plus,left,...) and replace it with the one just below it and presently commented out then everything is fine. Seems like display_expr is not appy with function applied to more than one argument.
Unless there's something stupid in my code.
Essentially, what you're doing is: BOOST_TYPEOF(some + proto + expr) e = some + proto + expr; // Use e It doesn't work quite like this. The reason why is that "some + proto + expr" is a tree where some of the nodes are temporary objects, which are held by reference by other nodes. It's a castle in the air, and at the semicolon, it crashes down. You need proto::deep_copy(): BOOST_TYPEOF(proto::deep_copy(some + proto + expr)) e = proto::deep_copy(some + proto + expr); // Use e Or even better: BOOST_PROTO_AUTO(e, some + proto + expr); which does the deep_copy for you. -- Eric Niebler Boost Consulting www.boost-consulting.com