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A general description is here.
‘selectMethod(f, ..)’ now keeps the function name if the function belongs to a group generic and the method is for the generic.
A C23 compiler (if available) is now selected by default for compilation of R and packages. R builds can opt out _via_ the ‘configure’ flag ‘--without-C23’, unless the specified or default (usually ‘gcc’) compiler defaults to C23: ‘gcc’ 15 does.
A C23 compiler is known to be selected with ‘gcc’ 13-15 (as used on Windows), LLVM ‘clang’ 18-20 (and 15 should), Apple ‘clang’ 15-17 and Intel 2024.2-2025.0 (and 2022.2 should).
Current binary distributions on macOS use Apple ‘clang’ 14 and so do not use C23.
R on Windows by default uses pkg-config for linking against external libraries. This makes it easier to test R and packages with alternative toolchains (such as from Msys2, e.g., testing with LLVM and possibly with sanitizers). It also allows more significant Rtools updates within a single R minor release.
The installer scripts for Windows have been tailored to Rtools45, an update of the Rtools44 toolchain. It is based on GCC 14. The experimental support for 64-bit ARM (‘aarch64’) CPUs is based on LLVM 19. R-devel is no longer maintained to be buildable using Rtools44 and it is advised to switch to Rtools45.
‘factanal()’ now works correctly also, e.g., for ‘GPArotation’, ‘oblimin()’ rotations, fixing PR#18417, thanks to Coen Bernaards and others.