On 04/26/2005 05:22 PM, Giovanni P. Deretta wrote: [snip]
As your code demonstrates, enumerators can be used without duplicating information, but an enum and map enum->type is required for each tuple. This is verbose and should be wrapped in a macro. Then again, I don't
Agreed.
like macros a lot :)
But mpl and fusion are profuse with macros, or at least boost/preprocessor.
In the end, getting 'by type' has the same expressive power of using enumerators, i simply think that it would have a better syntax and it would work out of the box with all tuples without the need of a map.
But it wouldn't work for repeated types, unless, as you noted previously, some sort of "tag" were "associated" with the type, which is what an mpl::map does, only it assures there's only one type associated with each tag; whereas the example: tuple<mpl::list<element1_type, element1_tag>, mpl::list<element2_type, element2_tag>,.....> in one of your previous messages: http://article.gmane.org/gmane.comp.lib.boost.devel/122595 doesn't assure this, AFAICT. Also, I'd think mpl::pair would be more succinct. So, the tuple version of the following: struct employ { string name; float salary; int ssn; }; could be: struct name{}; struct salary{}; struct ssn{}; tuple < mpl::pair<string,name> , mpl::pair<float,salary> , mpl::pair<int,ssn>
::type;
which is not that much shorter than the enum_map_0 shown in my previous post: http://article.gmane.org/gmane.comp.lib.boost.devel/122661 After all, for each enum_map_0::f_i, for i=0..2, there's got to be a tag with your method: struct name{}; struct salary{}; struct ssn{}; and there's also got to be a pairing of tags to types, just as in the enum_map_0::field_map. Am I missing something?