Bad array indexing is considered deadly

[Moritz Maxeiner via Digitalmars-d]

On Thursday, 1 June 2017 at 00:11:10 UTC, Timon Gehr wrote:
> On 01.06.2017 01:55, Moritz Maxeiner wrote:
>> On Wednesday, 31 May 2017 at 23:40:00 UTC, Timon Gehr wrote:
>>>>
>>>> In the context of the conversation, and error has already 
>>>> occurred and the all cases was referring to all the cases 
>>>> that lead to the error.
>>> Bounds checks have /no business at all/ trying to handle 
>>> preexisting memory corruption,
>> 
>> Sure, because the program is in an undefined state by that 
>> point.
>
> What does that even mean?

That once memory corruption has occurred the state of the program 
is not well defined anymore.

> Everything is perfectly well-defined here:
>
> void main(){
>     auto a = new int[](2);
>     a[2] = 3;
> }

Sure, because there has been no memory corruption prior to the 
index out of bounds.
That is not something the runtime should just assume for every 
out of index error.

>
>> There is only termination.
>> ...
>
>
> Termination of what? How on earth do you determine that the 
> scope of this "undefined state" is the program, not the 
> machine, or the world?

As that is the closest scope current operating systems give us to 
work with, this is a sane default for the runtime. Nobody stops 
you from using a different scope if you need it.

> I.e., why terminate the program, but not shut down the machine 
> or nuke the planet?
>
> Scoping really ought to be up to the programmer as it greatly 
> depends on the actual circumstances.

Of course, and if you need something else you can do so.

> Program termination is the only reasonable default behaviour, 
> but it is not the only reasonable behaviour.

Absolutely; rereading through our subthread I realized that I had 
not made that explicit here (only in other subthreads). I 
apologize for being imprecise.