Re: Boost.URL -- some notes

From: Peter Dimov (pdimov_at_[hidden])
Date: 2022-06-04 23:10:09

Andrzej Krzemienski wrote:
> Next, we read:
> 
> Aliases for standard types, such as string_view
> > <https://master.url.cpp.al/url/ref/boost__urls__string_view.html>, use
> > their Boost equivalents.
> >
> 
> After reading this, I expected that Boost.URL would use boost::string_view
> from Boost.Utility library:
> https://www.boost.org/doc/libs/1_79_0/libs/utility/doc/html/utility/utilities/s
> tring_view.html
> 
> But instead, it uses boost::core::string_view, which is an implementation detail
> from Boost.Core library:
> https://github.com/CPPAlliance/url/blob/master/include/boost/url/string_vie
> w.hpp
> 
> Again, this is news for me that Boost has two implementations of string_view.
> Why? Second, I do not think that Boost.URL should rely on the
> implementation details of Boost.Core. A better alternative would be to use the
> official boost::string_view from Boost.Utility. Or is there a good reason not to?

boost::core::string_view is convertible from/to std::string_view, which allows
user code to pass std::string_view to a library's functions and store their return
values into a std::string_view. This is a feature users request _very_ often
nowadays since C++17 is common.

We have proposed that these conversions be added to boost::string_view, but
there were concerns that they won't work well in practice because of creating
a mess of ambiguities. Which they kind of do, but it can be made to work. So
boost::core::string_view is that boost::string_view, we have it because we can
now try using it in library APIs and see if it's worth the bother. (So far it seems
to be.)

Where we go from here is undetermined yet. Maybe we integrate it into
boost::string_view and retire the Core one, maybe we undelete the
documentation of the Core one and make it official. I'd prefer to see it used
in a released Boost library or two first, for a release or two. If it works, we
decide what to do with it.

There's been a discussion here about it:

https://lists.boost.org/archives/boost/2021/10/252092.php