Nullable or Optional? Or something else?

[Steven Schveighoffer]

On Thu, 03 Sep 2009 11:50:55 -0400, Leandro Lucarella <llucax at gmail.com>  
wrote:

> Steven Schveighoffer, el  3 de septiembre a las 11:22 me escribiste:
>> On Thu, 03 Sep 2009 10:40:13 -0400, Leandro Lucarella

>> >Maybe this is a very silly question, but what is exactly the difference
>> >between Optional!T o/isNull(o) and T* o/o is null?
>>
>> The difference is you don't have to store the T somewhere else.
>
> That doesn't seems like a big problem having a GC.

There are performance concerns, you need 16 bytes minimum to store a value  
on the heap, so a 4-byte integer becomes 16 bytes on the heap.  And the GC  
is way slower than storing on the stack.

>
>> That is, an Optional!T contains both the value if it is not null AND
>> whether it is null or not.  With a T*, the value is stored elsewhere,
>> and you may have aliasing problems.
>
> Ok, this seems like a reasonable point. So Optional!T is a value type,
> right?

If T is a value type, yes.  I'm not sure what Andrei has in mind if T is a  
reference type.

-Steve