Re: [boost] Proposal for adding C++ level to the meta/libraries.json

-----Original Message----- From: Boost On Behalf Of Rainer Deyke via Boost Sent: 23 September 2020 12:16 To: boost@lists.boost.org Cc: Rainer Deyke Subject: Re: [boost] Proposal for adding C++ level to the meta/libraries.json

On 23.09.20 10:38, Paul A Bristow via Boost wrote:

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Why not just give a *range of requirements* for example: "C++11 to C++17"?

To me, that reads as "the library does not with C++20" or "the library is rendered obsolete by C++20", not "the library has no features that C++20".

OK - I see the scope for confusion. How about A *range of MINIMUM requirements* for example: "C++11 to C++17"?

I'm actually very interested in when a library is rendered obsolete by a C++ standard. Lots of Boost libraries have equivalents in the C++ standard library, or in some cases in the language itself. In some cases, the standard library component has completely rendered the Boost version obsolete. In some cases, the Boost version only exists as a backport of the standard library component, and was never intended to be used in C++ versions that include that component. In some cases, the Boost version and the standard library component have developed in different directions, and both are viable. And in some cases, the Boost version exists to correct a perceived flaw in a standard library component, so the Boost version should probably be preferred. It is often not clear which of these applies to which library, even after reading the library documentation (which may predate the standard library component).

Some examples: - Boost.Assign looks like it has been rendered obsolete by std::initializer_list, but maybe it still has some functionality that std::initializer_list cannot handle? - Boost.Atomic: the short library description "C++11-style atomic<>" implies a backport of C++11 functionality to C++03, but I don't know if that's actually the case. - Boost.Variant[2]: I know that Boost.Variant predates std::variant, which in turn predates boost::variant2, but neither of these libraries provides a simple and clear explanation of how it differs from std::variant.

Doesn't (or shouldn't) all Boost libraries just redirect to use the standard library when appropriate (without loss of features)? This allows continued use by unfortunates stuck with VS 6 as well the luckier VS latest trackers. I see this as a Boost USP. Paul