8/19/2026 at 10:55:47 AM
>“We must minimize the need to change existing code. For adoption in existing code, decades of experience has consistently shown that most customers with large code bases cannot and will not change even 1% of their lines of code in order to satisfy strictness rules, not even for safety reasons unless regulatory requirements compel them to do so.”But the major players do seem to be happy to replace their C++ code with Rust.
Perhaps it's time to ease up on the backwards compatibility. Especially in the era of AI.
by tonyedgecombe
8/19/2026 at 12:00:46 PM
> But the major players do seem to be happy to replace their C++ code with Rust.Because incremental improvements don't provide enough value. A stable C++ codebase is best left untouched. It's not worth to rewrite C++ into C++++ to get a couple of features that are flawed retrofits backported from modern languages. In the end you still have C++.
by pornel
8/20/2026 at 7:58:55 AM
The set-up and your reply feel like a Rust sketch.Not touching a codebase only applies to legacy software which is feature complete. Any actively developed software will benefit from incremental improvements.
Quality C++ projects continuously improve their code and tooling. It would be very convenient for the rustafarian community if the competition stood still, but that’s not the case. Quite happy to see that golang’s also providing solid opposition.
by blub
8/20/2026 at 11:17:43 AM
Note that an incremental language improvement doesn't mean a small code change. For example, C++'s iterator with two related but technically independent pointers is a PITA for alias analysis, which is a problem not only for Circle/Safe C++ but for WG21 Profiles too (https://www.circle-lang.org/draft-profiles.html). An incremental language change would be to adopt a Rust-like iterator. That would be a small language change, but a migration away from begin/end would be a massive churn for C++ codebases that sounds more ridiculous than rewriting in Rust.Bjarne still sees C++'s safety problem as lack of adoption of Modern C++. WG21 is catering to C++ users who will not make such changes.
WG21 has firmly rejected everything resembling Rust's borrow checking (a solution that now has a decade of proven track record, and has been demonstrated to be possible in C++ via Circle/Safe C++). Addition of "pervasive annotations" is so unacceptable to WG21's view of C++ that they're still insisting on Profiles.
by pornel
8/19/2026 at 1:08:55 PM
> But the major players do seem to be happy to replace their C++ code with Rust.I would be wary of mindlessly referring to appeals to authority like this. Sometimes their rationale is very context sensitive. For example, Microsoft has been behind quite a heavy push for C#, and it wouldn't be wise to use that as an example of C# being preferable to C++. See for example Bun's recent migration to Rust which could be misinterpreted as an example supporting migrating to rust, but under the hood it's far from a success story.
by locknitpicker
8/19/2026 at 1:29:29 PM
> Bun's recent migration to Rust which could be misinterpreted as an example supporting migrating to rust, but under the hood it's far from a success story.Since you don't mention that this migration is basically executed agenticly by Claude, it seems like you attribute this troubled migration to Rust not being that good of an improvement after all. For me it doesn't seem that surprising that Claude autonomously translating hacky Zig (according to Andrew Kelly #1) to unidiomatic (way more unsafe code that usual) Rust didn't solve the issues that the original code base already had.
#1 https://andrewkelley.me/post/my-thoughts-bun-rust-rewrite.ht...
by simon_void
8/20/2026 at 10:19:07 AM
> Since you don't mention that this migration is basically executed agenticly by Claude, it seems like (...)That's immaterial to the discussion.
by locknitpicker
8/19/2026 at 10:41:24 PM
Replace C++ code with Rust is happening at a glacial pace, basically involving full rewrites of the module replaced and significant work to refactor the surrounding code to support it.(This is why Rust is focusing heavily on interop right now, if it is easier to integrate more projects can use it)
The problem is updating a decently sized program from one version of a compiler to another can take man months to do and that doesn't typically include intentional breaking changes.
A C++ change that requires updating 1% can be several hundreds of thousands of updates which is on the scale of beyond a man year depending on if you can regex cheat.
The fear the author is glossing over (I wouldn't say ignore they acknowledge there are reasons) is when faced with a man year to update people just don't.
Especially when the most interesting breaking changes don't tend to be synthetic (you can just make modules look like code you couldn't write before after all) but instead be subtle changes in behavior.
That means that you won't necessarily even know all the breakages which is a horrifying concept.
by Guvante
8/19/2026 at 11:16:19 AM
Haskell has a pretty good story about how to use different dialects in the front end of the language, as long as the backend is still the same. Well, when I say Haskell, I mean ghc.Alas, C++ still mostly does its libraries via conceptual copy-and-paste (#include). So that would need to be fixed, if you wanted to mix-and-match dialects. You could probably keep '#include' syntax, but subtly change its meaning.
by eru
8/19/2026 at 9:46:12 PM
They seem willing to gradually replace C++ with Rust, but that actually does require C++ to not change in backward incompatible ways. They're depending on a stable ABI when calling into Rust.by nitwit005
8/20/2026 at 7:53:23 AM
Don’t believe everything you read. Any communication from them is a PR exercise.On the other hand, I read an interesting substack blog from an ex-Azure employee the other day: the Russinovich-dictated Rust rewrite was allegedly vaporware for a long time and caused lots of headaches that were not widely known. A highlight for me was the use of over 1000 third party crates in their products.
Would be interesting to know how it’s going nowadays.
As any company, the one I work for also has its decent share of rustafarians. The Rust penetration is modest and slow, but the PR is remarkable.
by blub