On Tue, 3 Jun 2025, 19:29 Simon Schröder via Std-Proposals, <
std-proposals_at_[hidden]> wrote:

>
> On Jun 1, 2025, at 10:32 AM, Thomas Krogh Lohse via Std-Proposals <
> std-proposals_at_[hidden]> wrote:
>
> I’d love to hear your thoughts:
> * Do you see value in defining a "safe-by-default" C++ subset with
> opt-in unsafe features?
>
>
> “Safe-by-default” will not work. C++ always tries to be backwards
> compatible and old (currently correct) code might not compile with your
> feature on.
>

Narrowing conversions became ill formed. Some lambda captures have been
deprecated (and are not ill formed? I don't remember). Asymmetric equality
operators became ill formed.

I don't think "old code must compile" is always such a hard line.


Currently, there are several proposals for so-called profiles (
> https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3589r0.pdf can
> give a good start into this topic with additional references at the bottom
> of this proposal).
>
> Your work should nicely fit into these profiles or add a new profile. Some
> of it is quite closely related, though profiles don’t discuss a borrower
> checker, yet. “Safe-by-default” could, however, be a compiler flag that
> turns on certain profiles by default. This might be the safest you can get
> without running against some of the core C++ philosophies.
>
> (The goto discussion could also be solved by profiles.)
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