Is it by design that `<string_view>` provides most contents of `<string>`?

[frederick-vs-ja]

MSVC STL's <string_view> currently directly includes <xstring>, which provides most contents of <string>.

I think it's OK for <string> to include <string_view> (since C++17). But when one only includes <string_view>, perhaps it's sometimes expected that no mechanism of dynamic allocation is made available.

If the status quo is not by design, I think we may extract the mechanisms of char_traits into a new internal header and make <string_view> slimmer.

[StephanTLavavej]

We talked about this at the weekly maintainer meeting and we don't remember why it was done this way. Extracting both char_traits and basic_string_view into an internal header (above <xstring>, e.g. <__msvc_string_view.hpp>) would allow <string_view> to avoid dragging in basic_string. We don't expect that extracting char_traits by itself would be useful, as any usage of char_traits is virtually certain to need either basic_string_view or basic_string.