On Mon, 24 Oct 2022 at 19:01, Matt Heath via Std-Proposals <
std-proposals_at_[hidden]> wrote:

> It is sometimes useful to treat an optional type as being a range with
> either one or zero elements. Rust has this feature, by making std::option
> implement IntoIterator. In C++ this would mean implementing overloads of
> std::begin and std::end taking std::optional<T> (and const std::optional)
> with :
> std::next(std::begin(op)) == std::end(op)
> if o.has_value(), and
> std::begin(op) == std::end(op)
> otherwise.
>
> This would mostly be for piping a range of optionals into std::join to
> leave just the unwrapped values, as in:
> std::vector<std::optional<int>> opts = {1, 2, std::nullopt, std::nullopt ,
> 3 };
> for(int n : opts | std::join )
> std::cout << n << " , ";
> This has the benefit of avoiding the programmer having to call has_value()
> and value() explicitly, which I think is probably for the best in terms of
> safety.
>

I think you want P1255 "views::maybe" [and "views::nullable"].

You'd need to transform the opts, possibly:

for(int n : opts | std::views::transform(std::views::nullable) | std::join)

https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p1255r9.pdf