Pointers - Is it safe to point to invalid memory?

[H. S. Teoh]

On Sat, Aug 16, 2025 at 10:28:15PM +0000, Andy Valencia via Digitalmars-d-learn wrote:
> On Saturday, 16 August 2025 at 21:58:30 UTC, Paul Backus wrote:
> > Creating a pointer that points out-of-bounds does not, by itself,
> > result in undefined behavior.
> > 
> > However, such a pointer would not be considered a [safe value][1],
> > because dereferencing it *would* result in undefined behavior.
> 
> I'm just pondering whether the intention was to accomodate this
> looping pattern:
> 
> ```d
> int sum_values(int* p, uint nval) {
>   int result = 0;
>   foreach(_; 0 .. nval) {
>     result += *p++;
>   }
>   return result;
> }
> ```
> 
> A C idiom (I've so very much embraced not using pointers in my D
> world) which technically leaves "p" pointing beyond the memory range.
> Perhaps this is the special case being addressed?
[...]

Why does it need to be addressed?  D has arrays and slices that know
their own length.  From p and nval you can form the slice p[0 .. nval]
which lets you iterate safely without risking illegal memory accesses:

	int sum_values(int[] arr) {
		int result = 0;
		foreach (i; arr) {
			result = i;
		}
		return result;
	}


T

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