Denis Koroskin wrote:
On Tue, 03 Mar 2009 21:59:16 +0300, Andrei Alexandrescu
<seewebsiteforem...@erdani.org> wrote:
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
If nullable is the default and NonNull!(T) has no syntactic sugar, I bet
it won't be used at all. I know I woudn't, even though I'm one of the
biggest advocates of introducing non-nullable types in D.
In my opinion, you should teach novices safe practices first, and
dangerous tricks last. Not vice-versa.
If using of nullable types would be easier that non-nullable once, it
won't be widely used. The syntax ought to be less verbose and more clear
to get an attention.
I hope that this great idea won't get spoiled by broken implementation...
I did some more research and found a study:
http://users.encs.concordia.ca/~chalin/papers/TR-2006-003.v3s-pub.pdf
Very interestingly (and exactly the kind of info I was looking for), the
study measures how references are meant to be in a real application of
medium-large size.
Turns out in 2/3 of cases, references are really meant to be non-null...
not really a landslide but a comfortable majority.
Andrei
