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C++ needs to just steal the idea of Epochs from Rust https://vittorioromeo.info/index/blog/fixing_cpp_with_epochs.html https://vittorioromeo.info/index/blog/fix

by wscott 6y ago

C++ needs to just steal the idea of Epochs from Rust https://vittorioromeo.info/index/blog/fixing_cpp_with_epochs.html https://vittorioromeo.info/index/blog/fixing_cpp_with_epochs... By default, everything is backward compatible, but to use new features you need to declare this compilation unit as being part of C++23 (or 26, 29). Then code that uses the new stuff also ignores the old and can have different rules. But it can still be combined with legacy code and libraries. You know at compile and linking time when crossing boundaries and can do the right thing. This actually combines nicely with modules since we already need a new build infrastructure to take advantage of modules.

plq 6y ago
Nothing is stopping you from passing different -std=c++XY arguments to different compilation units in your codebase. I don't know about other compilers but object files compiled with msvc, gcc and clang (the ones I happen to work with) using different -std values (starting with c++11) are compatible* and the respective teams working on these compilers reportedly make conscious efforts to make sure this remains the case. CMake for instance makes this very easy with its set_properties() call. * Of course there are caveats and corner cases. See eg. https://stackoverflow.com/questions/46746878/is-it-safe-to-link-c17-c14-and-c11-objects https://stackoverflow.com/questions/46746878/is-it-safe-to-l... But these seem like they could easily be avoided in real-world use-cases.
- wscott 6y ago
  Yes I can add new features to some files or I can compile with c++17 and link to an old C library. What I can't do is remove features or change the default calling conventions/ABI and still link with old code. If you declare in the interface and in the code that this is new code with new rules then this is possible. When you cross library boundaries the compiler adjusts. That is what rust allows and what C++ could do.

by wscott 6y ago

plq 6y ago

Nothing is stopping you from passing different -std=c++XY arguments to different compilation units in your codebase. I don't know about other compilers but object files compiled with msvc, gcc and clang (the ones I happen to work with) using different -std values (starting with c++11) are compatible* and the respective teams working on these compilers reportedly make conscious efforts to make sure this remains the case. CMake for instance makes this very easy with its set_properties() call. * Of course there are caveats and corner cases. See eg. https://stackoverflow.com/questions/46746878/is-it-safe-to-link-c17-c14-and-c11-objects https://stackoverflow.com/questions/46746878/is-it-safe-to-l... But these seem like they could easily be avoided in real-world use-cases.

wscott 6y ago
Yes I can add new features to some files or I can compile with c++17 and link to an old C library. What I can't do is remove features or change the default calling conventions/ABI and still link with old code. If you declare in the interface and in the code that this is new code with new rules then this is possible. When you cross library boundaries the compiler adjusts. That is what rust allows and what C++ could do.