foreach() behavior on ranges

[Joseph Rushton Wakeling]

On Tuesday, 24 August 2021 at 09:15:23 UTC, bauss wrote:
> A range should be a struct always and thus its state is copied 
> when the foreach loop is created.

That's quite a strong assumption, because its state might be a 
reference type, or it might not _have_ state in a meaningful 
sense -- consider an input range that wraps reading from a 
socket, or that just reads from `/dev/urandom`, for two examples.

Deterministic copying per foreach loop is only guaranteed for 
forward ranges.