Fixing C's Biggest Mistake

[Walter Bright]

On 12/30/2022 1:07 PM, Timon Gehr wrote:
>> In your description of pattern matching checks in this thread, the check was 
>> at runtime.
>> ...
> 
> No, the check was at compile time.

The pattern matching is done at run time.

> The check I care about is the check for 
> _failure_. The check for _null_ may or may not be _necessary_ depending on the 
> type of the reference.
NonNull pointers:

   int* p = ...;
   nonnull int* np = isPtrNull(p) ? fatalError("it's null!") : p;
   *np = 3; // guaranteed not to fail!

Null pointers:

   int* p = ...;
   *p = 3;  // seg fault!

Which is better? Both cause the program to quit on a null pointer.


> This technology has a proven track record.

A proven track record of not seg faulting, sure. A proven trackrecord of no 
fatal errors at converting a nullable pointer to nonnull, I'm not so sure.


 > Relying on hardware memory protection to catch the null
 > reference is never necessary,

If you manually code in a runtime check, sure, you won't need a builtin check at 
runtime.

 > because _valid programs should not even compile if
 > that's the kind of runtime check they would require to ensure type safety_.

Then we don't need sumtypes with pattern matching?

 > The hardware memory protection can still catch compiler bugs I guess.

Having a hardware check is perfectly valid for checking things.

BTW, back in the bad old DOS days, I used to write a lot of:

     assert(p != NULL);

It was very effective. But with modern CPUs, this check adds no value, and I 
removed them.