std.v2020.algorithm etc[ WAS: Is run.d going to be expand for runtime and the phobos library?]

[Steven Schveighoffer]

On 6/22/20 10:20 AM, Paul Backus wrote:
> On Monday, 22 June 2020 at 12:15:39 UTC, Steven Schveighoffer wrote:
>>
>> My question wasn't about how such a thing could be implemented, but 
>> how it works with const ranges.
>>
>> foreach(x; someConstRange) I think wouldn't be possible. I think you'd 
>> have to recurse:
>>
>> void process(const Range r)
>> {
>>    subProcess(r.front);
>>    process(r.rest);
>> }
>>
>> The point is to question the statement "so that we can have `const` 
>> and `immutable` ranges".
>>
>> Sure, we could implement recursive versions of find, etc. I don't know 
>> if that's worth it.
>>
> 
> Well, currently, range algorithms can't work with const ranges *at all*, 
> recursively or iteratively. So from a user perspective, this would be a 
> strict improvement on the status quo.

Algorithms can work with const ranges -- as long as the range is an array:

const int[] arr = [1, 2, 3, 4, 5];

auto x = arr.find(3);

assert(x == [3, 4, 5]);

I think the better option is to focus on making it possible to duplicate 
this possibility for generic ranges rather than implement a new and 
awkward API.

FeepingCreature is right, we should try and create a head mutable 
mechanism. I have envisioned it in the past as a tail-modifier mechanism 
(e.g. tail-const).

-Steve