[chakkepolja]

Apart from the mutable keyword, can't these be implemented as a clang diagnostic plugin? Then it can be used to enforce a stricter style guide. As another commenter pointed, mutable will be probably of limited use anyway.

[compiler-devel]

Yes, some (maybe most) could be implemented in a plugin. I wanted to make these changes in part to better understand the clang internals and also show that rather than use external tooling, the language itself can (should?) be changed.

[cweagans]

I would submit that C++ has enough inertia (as a language and as an ecosystem) that changing the language itself would be difficult.

However, C++ is a huge language and if there's a way to enforce safety by using only a subset of the language + tooling to help you do that, your improvements could be adopted piecemeal by teams looking to level up their codebase a bit.

Many languages have a way to opt in to e.g. strict type checking on a per-file basis. It would be really cool to see these improvements implemented in such a way that existing codebases could gradually adopt them.

[compiler-devel]

Thank you, this indeed is the approach that I'd like to take. Like I mentioned in the commit message on the patch, one of my goals is to show that we can iterate the language (and our codebases) gradually. I'll add a feature flag to my patch to selectively enable and disable these changes.