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 20:17:29 UTC, Steven Schveighoffer 
wrote:
> On 6/20/20 3:23 PM, 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.
>
> There are a few "base" ranges, like arrays, and data structure 
> ranges. The one common true "input-only" range is a 
> stream-based range (like File.byLine).

Thanks for the detailed reply, it's very helpful and I'm finding 
the discussion useful.

Another potentially useful example is a stream of random numbers, 
where it may be undesirable to allow the state of the random 
number stream to be copied.

> An input range is generally useful in foreach, and almost 
> nothing else.

Here I might disagree a bit. Nearly all the algorithms in 
std.algorithm.iteration (map, filter, fold, etc.) operate on 
input-only ranges. These are important classes of operations. 
They are largely alternate forms of foreach, so likely this is 
more clarification than disagreement.

Related thought: One-time iteration of a stream is common in many 
of the apps I write. I tend to think of such streams as logically 
input-only. Whether it's valid/legal to copy the stream at 
implementation level is a different question. More recently I've 
finding reasons to enforce at most once iteration, even if the 
underlying data structures (like an array) don't care.

--Jon