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

From: Rainer Deyke (rdeyke_at_[hidden])
Date: 2020-09-23 11:15:44

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

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.

-- 
Rainer Deyke (rainerd_at_[hidden])