use boost::core::string_view

[vinniefalco]

We should use boost::core::string_view instead of boost::utility::string_view, because it has better interoperability with std::string_view. However, before we make this change public we need to write a short matrix of tests that mix the three principle string views and the standard string std::string, std::string_view, boost::utility::string_view, boost::core::string_view in order to understand what compatibility problems users may experience (if any).

[sehe]

I've created a whole slew of test-cases to excavate differences between various implementations. These are not up to standard for inclusion, but perhaps someone sees some useful bits?

Goggles advised: https://github.com/sehe/beast/blob/core_string_view/test/beast/core/string.cpp

Note it uses c++17 for brevity - not in the last place to be able to compare with c++17 std::string_view, but liberally using contexpr and traits that are specific to c++17.

Differences between implementations that might be observed are marked OBSERVABLE

[sehe]

@vinniefalco Just realized another loose end: despite std::string_view compatibility, core::string_view still doesn't support some templated free functions, like

• std::quoted (too bad I guess)
• asio::buffer
• asio::const_buffer demo

The latter are a shame. They circle back to your discussion about custom buffer types in boost-http somewhat.

No regression or impact from the issue, just something we might want a solution to.

[sehe]

Status:

• IMO This should remain draft until boost::core::string_view is not hashable core#110 lands, to avoid inconveniencing Beast users with breaking change in their own code using beast::string_view

• @vinniefalco / @pdimov Do you see any mechanism to aid with the compatiblity with std::string_view for free function templates (std::quoted, asio::buffer and possible others in thirdparty code)? Perhaps there's already a niebloid like beast::buffer_bytes that I'm not aware of for this?

[pdimov]

What does "land" mean here?

[pdimov]

What are we supposed to do about std::quoted or asio::const_buffer?

[sehe]

The goal of this ticket is to make beast::string_view more compatible with std::string_view.

Both these free functions are std::string_view features, but not compatible with core::string_view. I'm just asking in case I'm missing some fancy way to address these?

[sehe]

@pdimov "landing a ticket" means when it ships in the next release (it will merge to master, basically). Wasn't aware that was company specific lingo :/

[pdimov]

It has been merged to master. Next release, well that's another story.

We can't change std::quoted, so I'm not sure what we can possibly do about it.

[vinniefalco]

What the heck is std::quoted

[pdimov]

It's a manipulator that quotes strings on op<< and unquotes them on op>>. https://godbolt.org/z/3srYsno9K

[sehe]

@pdimov That's awesome. Yeah, I had expected the merge to be visible on boostorg/core#110 but that wasn't a PR in the first place. Are you saying that things that are on master do not /automatically/ get pulled into the superproject next release?

[pdimov]

Yes, whatever's on master automatically goes into the next release. But the release itself is months from now.

[sehe]

That's fine, the Beast change would be in the same release. As long as they go together or in the right order, I'm not in a hurry.