Null references (oh no, not again!)

[Andrei Alexandrescu]

Daniel Keep wrote:
> Just noticed this hit Slashdot, and thought I might repost the abstract
> here.
> 
> http://qconlondon.com/london-2009/presentation/Null+References:+The+Billion+Dollar+Mistake
> 
>> I call it my billion-dollar mistake. It was the invention of the null
>> reference in 1965. [...] This has led to innumerable errors,
>> vulnerabilities, and system crashes, which have probably caused a
>> billion dollars of pain and damage in the last forty years. [...] More
>> recent programming languages like Spec# have introduced declarations
>> for non-null references. This is the solution, which I rejected in
>> 1965.
> 
>   -- Sir Charles Hoare, Inventor of QuickSort, Turing Award Winner

I suggested to Walter an idea he quite took to: offering the ability of 
disabling the default constructor. This is because at root any null 
pointer was a pointer created with its default constructor. The feature 
has some interesting subtleties to it but is nothing out of the ordinary 
and the code must be written anyway for typechecking invariant 
constructors.

That, together with the up-and-coming alias this feature, will allow the 
creation of the "perfect" NonNull!(T) type constructor (along with many 
other cool things). I empathize with those who think non-null should be 
the default, but probably that won't fly with Walter.


Andrei