Spec#, nullables and more

[Walter Bright]

Denis Koroskin wrote:
> On Fri, 05 Nov 2010 23:44:58 +0300, Walter Bright 
> <newshound2 at digitalmars.com> wrote:
>>
>> To eliminate null pointers is the same as shooting the canary in your 
>> coal mine because its twitter annoys you.
> 
> I'm tired of pointing out that NO ONE is talking about eliminating null 
> pointers, but rather extending an existing type system to support 
> non-nulls. Your hate towards non-nullables comes from misunderstanding 
> of the concept.

Consider non-nullable type T:

   T[] a = new T[4];
   ... time goes by ...
   T[1] = foo;
   T[3] = bar;
   ... more time goes by ...
   bar(T[2]);

In other words, I create an array that I mean to fill in later, because I don't 
have meaningful data for it in advance. What do I use to default initialize it 
with non-nullable data? And once I do that, should bar(T[2]) be an error? How 
would I detect the error?

In general, for a non-nullable type, how would I mark an instance as not having 
meaningful data?

For example, an int is a non-nullable type. But there's no int value that means 
"no meaningful value", and this can hide an awful lot of bugs.

I'm not sure at all that non-nullable types do more than make easy to find bugs 
much, much harder to find.