Range support for directory_iterator and recursive_directory_iterator

[Beman]

Description

Daniel Krügler [c++std-filesystem-29]

IMO the range-support for [recursive_]directory_iterator should be deferred.
The presented technique is IMO an unfortunate "hack" and should be
replaced by factory functions returning a
std::range<[recursive_]directory_iterator>.

The std::range is IMO the much better solution for this and idiomatic.

Yes, we have not yet std::range, but we nearly got that via a last-minute
proposal for C++11. I hope, this time we have a bit more time to make
a full-fledged
proposal.

I would strongly recommend to defer the range-support instead. We can work with
these iterators, they are not broken, several existing iterators
provide no direct
support for the range-for-loop. It is not a shame that
[recursive_]directory_iterator
would not at the initial proposal.

Adding a "cleaner" way via factory functions returning a
std::range<[recursive_]directory_iterator>
can be easily down slightly later.

Discussion

[Beman] I believe the Filesystem library should become a Technical Specification, and as such should rely only on C++11 features.

Deciding if the target is a TS or is C++1y needs to be deferred to a committee meeting so that input from the LWG (and possibly the EWG) is available. Thus an issue is being opened so Daniel's proposal isn't forgotten.