Making alloca more safe

[bearophile]

Walter Bright:

> I don't want to get into another loooong thread about should pointers be 
> nullable or not,

It was a good thread with good ideas.


>I just wished to point out that it was not a *safety* issue.<

A safe system is not a program that switches itself off as soon as there's a small problem.

One Ariane missile has self-destroyed (and destroyed an extremely important scientific satellite it was carrying whose mission I miss still) because of this silly behaviour united with the inflexibility of the Ada language.

A reliable system is a systems that keeps working correctly despite all. If this is not possible, in real life you usually want a "good enough" behaviour. For example, for your TAC medical machine, in Africa if the machine switches itself off at the minimal problem they force the machine to start again, because they don't have money for a 100% perfect fix. So for them it's better a machine that shows a slow and graceful degradation. That's a reliable system, something that looks more like your liver, that doesn't totally switch off as soon it has a small problem (killing you quickly).

A program that stops working in a random moment because of a null is not safe. (And even if you accept this, in safer languages like C#/Java there are null exceptions that show a stack trace. The type system is smart enough to remove most of those tests to improve performance). A safer program is a program that avoids null pointer exception because the type system has formally verified the program has no nulls.

Bye,
bearophile