On Thu, Sep 25, 2008 at 5:14 PM, Doug Gregor <dgregor@osl.iu.edu> wrote:
On Sep 25, 2008, at 9:32 AM, Joel de Guzman wrote:
Doug Gregor wrote:
The alternatively, of course, is to use a syntax like: case_<1>()[cout << val("one") << '\n', cerr << val("hello")], Interestingly, catch_<exception_type>()[ ... ] uses this same syntax; why the discrepancy between case_ and catch_? Or did I miss something?
Yeah, the discrepancy... It's one of the things I'm not quite satisfied with. I do like the brackets [] but the empty parens stick out like a sore thumb to me. At one point, I used the [] for the cases, changing it later to the (). Fickle, ain't I?
I'm open to suggestion. If we are to break the interface anyway, I'd follow what the community wants.
Personally, I don't find the extra ()'s in case_<1>() all that horrible, and I think it's the more regular to have all of the statements in []. That said, unless something *else* is breaking the interface, this isn't the thing that should be first to break the interface.
Hum, what about relaxing a little the 'C++ in C++ tag' and making switch_ more powerfull than the builtin switch? Instead of: switch_(arg1) [ case_<1>(cout << val("one") << '\n'), case_<2>(cout << val("two") << '\n'), default_(cout << val("other value") << '\n') ] do this: switch_(arg1) [ case(1)[cout << val("one") << '\n'], case(2)[cout << val("two") << '\n'], default_[cout << val("other value"] << '\n') ] this allows not only runtime selection of switch case values, but it will also work with everything that is equally comparable: switch_(arg1) [ case("one")[cout << val(1) << '\n'], case("two")[cout << val(2) << '\n'], default_[cout << val("other value"] << '\n') ] which IMHO is a killer feature. The fact that the case parameter is not a template parameter might limit compiler optimizations unless the the compiler is good at constant propagation, but there is a workaround: switch_(arg1) [ case(mpl::int_<1>())[cout << val("one") << '\n'], case(mpl::int_<2>())[cout << val("two") << '\n'], default_[cout << val("other value"] << '\n') ] Let's leave the ugly syntax to those that need it :) As another extension, when visiting heterogeneous sequences (think fusion::for_each), a switch by type would be great: switch_(arg1) [ case(type<std::string>())[cout << val("std::string") << '\n'], case(type<int>()) [cout << val("int") << '\n'], default_[cout << val("other type"] << '\n') ] (in this case switch_ would need to know about type<> because it must not compile the not-taken branches). Even better: switch_(arg1) [ case(type<std::string>())[cout << val("std::string") << '\n'], case(type<std::vector<_> >()) [cout << val("a vector of something") << '\n'], default_[cout << val("other type"] << '\n') ] -- gpd