On Sat, Sep 27, 2008 at 6:23 AM, Joel de Guzman <joel@boost-consulting.com> wrote:
Giovanni Piero Deretta wrote:
[snip about the switch_]
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.
Cool!
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 :)
It seems your proposal is compatible with this syntax anyway:
case<1>()[cout << val("one") << '\n'],
So you can choose one or the other.
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') ]
I love it! I think it's wonderful. Would you be interested in implementing this? :-P
Sure, I'll give it a try. -- gpd