On Thu, 11 Aug 2011 15:32:20 +0200, Timon Gehr <timon.g...@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
