Nullable Types

[Steven Livingstone]

I've just blogged some stuff on Nullable types in net 2.0.
http://stevenr2.blogspot.com/2006/01...oalescing.html

Question however as to why you can't simply get an implcit conversion from a
..Net value type to to a Sql Server data type rather than having to use null
cheked and DBNull.Value ?

Does anyone have some explanation as to why this is so tricky as to be
included?

http://stevenR2.com

[William Stacey [MVP]]

| I'm perfectly happy with nullable types - but we're missing one part of
| the quadrant, which is to be able to declare reference type variables
| which can *never* be null:

It just seems to me the driving force for null value types was SQL. As
without that, we would not really need them as we got along fine before. I
can remember once where I really needed a nullable value type and coded
around it and that was ok. Sure options can be a good thing, but dang, the
code matrix explodes with all this null testing going on. I have a dream.
Create a version of sql with .Net types only (and user defined types). Have
value types (no nulls) and ref types (allow nulls). Would seem to simplify
things end-to-end.

| string! x = "hello"; // Fine
| string! x = null; // Compiler complains

That would seem reasonable.

--
William Stacey [MVP]

[Jon Skeet [C# MVP]]

William Stacey [MVP] wrote:

| I'm perfectly happy with nullable types - but we're missing one part of
| the quadrant, which is to be able to declare reference type variables
| which can *never* be null:

It just seems to me the driving force for null value types was SQL. As
without that, we would not really need them as we got along fine before. I
can remember once where I really needed a nullable value type and coded
around it and that was ok.
Yes, you can code around it - but if lots of people are coding around
something, even if it's only required fairly occasionally, isn't it
better to have support for that such that it's only written once?
Sure options can be a good thing, but dang, the
code matrix explodes with all this null testing going on. I have a dream.
Create a version of sql with .Net types only (and user defined types). Have
value types (no nulls) and ref types (allow nulls). Would seem to simplify
things end-to-end.
Well, you can make sure you don't have nulls in your database now. Of
course, the results of doing a sum which matches no values would then
be undefined, etc...
| string! x = "hello"; // Fine
| string! x = null; // Compiler complains

That would seem reasonable.

We can but hope :)

(It would get rid of a lot of nullity checks in method calls, too - you
just make your method parameter a string! and then you don't need to
worry...)

Jon

[Scottie_do]

Speaking of quadrents and possibilities.. . it would be great to have a
reference of what can and can't be done in C# 1.0 and 2.0; Perrhaps with a
c++ overlay.

I'm sure that would get someone new to the language up to speed quick. If
anyone hasn't written such a grid already, I'll write one as long as someone
will critique it.

"Jon Skeet [C# MVP]" wrote:

William Stacey [MVP] <wi************ @gmail.com> wrote:

If you ask me, all this null stuff is confusing as heck. I got along just
find with no null value types. First thing Jim Gray does on all his tables
is not allow nulls. Now we also have "IsNull" and "Is Null" to worry about
on CLR UDTs and nullable value types in c#, and Uggg. I would like the old
days (~last year) with value types and ref types and ref types can be null
and get rid of null value types on SQL all together (right, that will
happen).

I'm perfectly happy with nullable types - but we're missing one part of
the quadrant, which is to be able to declare reference type variables
which can *never* be null:

string! x = "hello"; // Fine
string! x = null; // Compiler complains

(Just as an example.)

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
If replying to the group, please do not mail me too