std::views::as_rvalue() banned?

[Thomas Sepez]

Since we prefer constructing containers using the std::from_range constructor form over the two-iterator constructor form, a problem occurs with cases like this:

  std::vector<T> vec(std::make_move_iterator(that.begin()),

                     std::make_move_iterator(that.end()));

which is expressed in range form as

  std::vector<T> vec(std::from_range, std::views::as_rvalue(that));

but as_rvalue() is still banned. Thoughts?

[Jan Wilken Dörrie]

I doubt we'll allow std::views anytime soon, see https://groups.google.com/a/chromium.org/g/cxx/c/ZnIbkfJ0Glw for a related discussion.

For the case of std::views::as_rvalue there is the alternative base::RangeAsRvalues, which should allow you to do 

  std::vector vec(std::from_range, base::RangeAsRvalues(std::move(that)));.

In the case of vector, 

  auto vec = base::ToVector(that, [](auto& e) { std::move(e); });

should also work.

Best,

Jan

[Thomas Sepez]

Ah, thanks, good to know base/ already has this covered.