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

[Jon Degenhardt]

On Saturday, 20 June 2020 at 19:35:07 UTC, Paul Backus wrote:
> On Saturday, 20 June 2020 at 19:23:55 UTC, Jon Degenhardt wrote:
>> On Saturday, 20 June 2020 at 18:26:43 UTC, Steven 
>> Schveighoffer wrote:
>>> But the larger point is that true input-only ranges are rare. 
>>> The only problem is for classes, since you cannot invoke a 
>>> copy constructor on those.
>>
>> Interesting discussion. Could you expand on this comment? 
>> Several people have mentioned this.
>>
>> I write my own input ranges somewhat regularly. I've never had 
>> the need to make them forward ranges. However, the typical 
>> reason for creating a range is because I have application 
>> specific data that I want to iterate over (and usually 
>> construct) lazily. Input ranges are very convenient way to do 
>> this. I do end up making many of them reference ranges though.
>>
>> So, I'm wondering if its really that input-only ranges are 
>> rare, or if it's that the number of algorithms that can be 
>> used on input-only ranges is small. Or perhaps I'm not quite 
>> grokking the distinction between a "true" input-only range and 
>> one that satisfies isInputRange, but none of the other range 
>> primitive tests.
>>
>> --Jon
>
> Could you easily make your ranges into forward ranges if you 
> wanted to? That is, if you copy one of them, and then iterate 
> the original, does the copy remain valid? If so, they're not 
> "true" input ranges.
>
> A "true" input range is something like a file handle, where you 
> couldn't implement `save` even if you wanted to--iterating one 
> copy automatically invalidates all the others.

Ah, thanks for this clarification. I'd have to go back and look 
at all the different ranges I've written, but I'd say there are a 
fair number in both camps. Now I'm wondering if there's a 
correlation with the use of reference ranges. That is, have I 
used reference ranges when the range falls into the "true" input 
range set. The answer may be yes.