DB ORM

[Timon Gehr]

Simen Kjaeraas wrote:
> On Thu, 11 Aug 2011 15:32:20 +0200, Timon Gehr <timon.gehr at gmx.ch> wrote:
>
>> 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.
>
> Or, you know, a simple pointer? Avoids some of the overhead of the class
> solution.
>
> --
>    Simen

Well, sure. :)
But he was specifically asking for a nullable reference akin to what you get in C#.
I don't see how it is useful anyways.