Tests of C++20 as the default C++ standard
==========================================+

R last changed its default C++ standard to C++17 in R 4.3.0 ‘where
available’, and it is proposed to change this to C++20 ‘where
available’ in R 4.6.0 around April 2026 (and hence soon in R-devel).
Several CRAN packages already require C++20, including V8 which has
hundreds of reverse dependencies.

The logs in this directory were run using R-devel on the M1mac test system:
(see https://www.stats.ox.ac.uk/pub/bdr/M1mac/README.txt)

To test defaulting to C++20 for your own package(s) add something like

CXX = g++ -std=gnu++20

to ~/.R/Makevars.  (Copy the local version from R_HOME/etc/Makevars
and change 17 to 20.  For Windows, use ~/.R/Makevars.win.)

It will continue to be possible to force C++17 for a package by
specifying it(see ‘Writing R Extensions’).  However, this would be
unhelpful for packages which offer headers for LinkingTo as it may
force the other packages to use C++17, so such packages should be
modernised.

GCC and GNU's libstdc++ are often slow to implement C++ deprecations
and removals so not all the issues may be reproducible there.