DB ORM

[zhang]

> Graham Fawcett wrote.
> > On Thu, 11 Aug 2011 20:10:15 +0800, zhang wrote:
> >
> >>> > I think D needs user defined attributes first.
> >>
> >> About attribute, here is an example:
> >>
> >> ....
> >>
> >> There is a problem that is D's basic type is not nullable. In C#,
> >> the nullable integer type can be defined as "Int?" or
> >> "Nullable<int>".
> >
> > You don't need attributes for that: you can just define a "struct
> > Nullable(T)" that wraps the value, and provides a way to express a
> > null value.
> >
> >     struct Person {
> >       int ID;           // required
> >       Nullable!int age; // optional
> >       ...
> >     }
> >
> >     void foo(Person p) {
> >       if (p.age.isNull) ...
> >       else writeln(p.age + 100);
> >     }
> >
> > Graham
> 
> Alternatively you just use a class to wrap the value:
> 
> template Nullable(T){
>     static if(is(T == class)) alias T Nullable;
>     else class Nullable{T v; alias v this;}
> }
> 
> 
> The benefit of this approach is that you don't have to invent new ways to test for
> null values.

That's it. So, the nullable basic type is not a problem. Thanks.
----------
Zhang <bitworld at qq.com>