Eric Niebler <eric@boost-consulting.com> writes:
Well, it's not ideal for that because it requires a runtime function call. But then again, so do proto's operator overloads. This is the sort of thing where you would want to leverage the POD-ness of proto's expr<> type. Consider:
// 1 + "hello" proto::plus< proto::terminal<int>::type , proto::terminal<char const *>::type
::type const int_plus_string = {{1}, {"hello"}};
This thing requires no runtime initialization. And if you peek at libs/xpressive/proto/test/lambda.cpp, check out the lambda<> expression wrapper. It shows a way to extend a proto expression type without losing POD-ness, so you can make the above still work.
I'll take a look at the lambda example again, but in this particular case I'll probably stay with the deep_copy approach: I'll have maybe 10-20 of those expressions and they'll be initialized at startup and I think explicit expressions make the intent clearer. But unless I find other problems, I'll try to make my expressions PODs. That should be good regardless.
If you'd rather go the deep copy route, you don't need to wait for me to fix proto::deep_copy(). You can accomplish the same thing with a proto transform. Here is some code to get you started. It deep-copies a proto expression, and wraps everything in a myexpr<> wrapper.
Thanks for the code. I'll use the fixed deep_copy, but it is always educational. Regards, Maurizio