Nullable types

[Lionello Lunesu]

samabeau wrote:
> Lionello Lunesu Wrote:
>  
>> * Are there any other languages with this concept?
> 
> C# does. Nullable types have a question mark after them.
> eg:-
> 
> int? num = null;
> 
> http://msdn.microsoft.com/en-us/library/1t3y8s4s(VS.80).aspx
> 

In C#, that "?" basically wraps (boxes?) a value type into a reference 
type.

Once you have an object reference (either an instanced class or such a 
wrapped value type) you still must check for null everywhere you use it. 
And in some situations you just know it's never null and you would like 
to use that information.

At the moment, the way you can tell that an object is never null is by
(1) using an assertion;
(2) mentioning it in a comment;
(3) using some hungarian-like naming scheme;

None of which have any value at compile-time. In fact, if you think 
those 3 alternatives are good enough, you could drop all the 
compile-time type checking.

And what happens nowadays when none of those 3 is present? You check for 
null, whether the check makes sense or not. If I'd only get a penny for 
every if-null check I've encountered...

Letting the type system track whether a reference is null or not should 
result in more readable code. No more wondering "What if x is null? 
Where's it checked?" and no more "let's check for null, just in case."

L.