2016-02-18 15:43 GMT+01:00 Mazola Winstrol <mazofei...@gmail.com>: > Em 18/02/2016 10:12, "Marco van de Voort" <mar...@stack.nl> escreveu: >> >> In our previous episode, Mazola Winstrol said: >> > end; >> > >> > >> > Suppose that this class represent data of the Person table in a sql >> > database. Suppose that there is records where the column "BirthDate" is >> > null. How do i represent a null "BirthDate" in my object? >> >> Keep using variants instead of typed data. >> > > I think this is not a good alternative. As the variant are untyped, should > the consumers of the person class assume that BirthDate are filled as a > formated date string '01/01/1980' or as a native tdatetime? > > I think it would be better using record wrappers to primitive types. See > http://blogs.embarcadero.com/abauer/2008/09/18/38869. > > What do you think about that?
Personally, I like the Nullable<T> idea from C#, which is basically a generic record adding a "HasValue: boolean" to "Value: T". The type-safety is nice, and it's sometimes very useful (when you cannot "cheat" and say that "empty string" or "zero value" always means "uninitialized"). Looking at your link http://blogs.embarcadero.com/abauer/2008/09/18/38869 , this is exactly trying to implement Nullable<T> in Object Pascal. The major problem there is that it's difficult to force it to be always initialized with zeroes. Currently, a non-global variable of unmanaged type can always be filled with memory garbage, as explained in other thread. The trick in http://blogs.embarcadero.com/abauer/2008/09/18/38869 to use interfaces feels ugly, it's an over-use of the "interface" specifics in Object Pascal. I remember a thread on fpc-devel "Pascal Smart Pointers Idea + ARC implementation" where the original author (Maciej Izak) was already working to overcome this: https://www.mail-archive.com/fpc-devel@lists.freepascal.org/msg33172.html . His reasons was similar (force the contents to be initialized with zero) and his solution felt cleaner -- introduce "class operator Initialize" where you can initialize your record. Any chance that this would be added/merged to FPC one day?:) Regards, Michalis _______________________________________________ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
