Spec#, nullables and more

[Walter Bright]

Adam Burton wrote:
> I wouldn't consider that as the same thing. null represents the lack of a 
> value where as 25 is the wrong value. Based on that argument the application 
> should fail immediately on accessing the item with 25 (not many moons later) 
> in the same manner it does nulls, but it doesn't because 25 is the wrong 
> value where as null is a lack of value.
> 
> As with the array allocation example earlier you initialise the array to 
> nulls to represent the lack of value till your application eventually gets 
> values to assign to the array (which may still be wrong values). As shown by 
> my alternative example non-nulls allow you to define that a 
> variable/parameter wants a value and does not work when it receives nothing. 
> However in the case of the array because all the information is not there at 
> the point of creation it is valid for the array items to represent nothing 
> till you have something to put in them.


I am having a real hard time explaining this. It is conceptually *the same 
thing*, which is having an enforced subset of the values of a type.