Spec#, nullables and more

[tls]

Roman Ivanov Wrote:

> On 11/6/2010 2:14 PM, Walter Bright wrote:
> > Rainer Deyke wrote:
> >> On 11/6/2010 02:42, Walter Bright wrote:
> >>> Adam D. Ruppe wrote:
> >>>> It wasn't until I added the invariant and in/out contracts to all the
> >>>> functions
> >>>> asserting about null that the problem's true cause became apparent.
> >>> Couldn't this happen to you with any datum that has an unexpected value
> >>> in it?
> >>>
> >>> Suppose, for example, you are appending the numbers 1..5 to the array,
> >>> and somehow appended a 17. Many moons later, something crashes because
> >>> the 17 was out of range.
> >>
> >> That's an argument for limited-range data types, not against
> >> non-nullable types.
> > 
> > I see it more as an argument for any restricted subset of a data type.
> > It could be that you want just odd numbers in the array, and an even one
> > crept in.
> 
> Not quite. I don't want to make an argument in favor of general subsets
> of data types. (IMO it can be made, but that's a topic of a different
> discussion.) I just want to point out that nulls are a special case,
> because they allow anyone to bypass (effortlessly, often unknowingly!)
> the type checks enforced by class system, which is probably the most
> important part of object-oriented programming.

The silent break when nulls is on purpose right? To make coding easy and fun. I not want test null everywhere. School taught Java and remember nonnull always makes stupid tests and exceptions :-(