Null references redux

[Christopher Wright]

Walter Bright wrote:
> Denis Koroskin wrote:
>> If an object may or may not have a valid value, you mark it as 
>> nullable. All the difference is that it's a non-default behavior, 
>> that's it. And a user is now warned, that an object may be not 
>> initialized.
> 
> He isn't warned, that's just the problem. The null object happily says 
> "I succeeded" for all input and returns more default values and null 
> objects.

This is not the proposal. The proposal was to codify in the type system 
whether a particular object has "null" as a valid value. If a variable 
that cannot be null is not initialized to a non-null value before use, 
that is an error.

It's entirely equivalent to using the current type system with a ton of 
manual contracts requiring that variables not be null. Except the 
contracts are enforced at compile time, not runtime.

A similar concept would be range-bounded integer types, or floating 
point types that cannot be NaN or infinity.