foreach() behavior on ranges

[Joseph Rushton Wakeling]

On Wednesday, 25 August 2021 at 17:01:54 UTC, Steven 
Schveighoffer wrote:
> In a world where copyability means it's a forward range? Yes. 
> We aren't in that world, it's a hypothetical "if we could go 
> back and redesign".

OK, that makes sense.

> Technically this is true. In practice, it rarely happens. The 
> flaw of `save` isn't that it's an unsound API, the flaw is that 
> people get away with just copying, and it works 99.9% of the 
> time. So code is simply untested with ranges where `save` is 
> important.

This is very true, and makes it quite reasonable to try to pursue 
"the obvious/lazy thing == the thing you're supposed to do" 
w.r.t. how ranges are defined.

> I'd be willing to bet $10 there is a function in phobos right 
> now, that takes forward ranges, and forgets to call `save` when 
> iterating with foreach. It's just so easy to do, and works with 
> most ranges in existence.

I'm sure you'd win that bet!

> The idea is to make the meaning of a range copy not ambiguous.

Yes, this feels reasonable.  And then one can reserve the idea of 
a magic deep-copy method for special cases like pseudo-RNGs where 
one wants them to be copyable on user request, but without code 
assuming it can copy them.