Don't we consider a C/C++ replacement "successful" when it was able to capture enough share of prior C/C++ uses, not the entire share? I never thought C or C++ could be completely gone out of sight, even COBOL is technically alive today (on life support). To be clear, I meant that D could have been in the position of Rust today if done right.
I wouldn't consider a C++ (or C) replacement PLₓ successful until the people working on big compiler toolchains—many of whom are committed alternative programming language advocates themselves (consider the origins of e.g. Swift and LLVM)—decide that, moving forward, those will be written in PLₓ rather than C++.
(Note that the bar I'm establishing here is not merely to have a self-hosted compiler (see many toy compilers). I'm talking about a hypothetical future milestone where the software world's core infrastructure comprising LLVM/Clang and* GCC is written in the "replacement language", i.e. the compilers for a bunch of other (non-PLₓ) languages—including C and C++—are written in PLₓ as well. The backends, at least.)
While I do hope that future, it is an unreasonably high bar because the main value of LLVM is that you don't have to make everything again to make your own PL implementation. For the same reason contemporary web browsers are unlikely to be fully rewritten in any other language unless they get completely displaced by newer browsers. (At least LLVM has a better chance of being replaced...)
A corollary of this is that a language probably needs to be able to interop with C++ to have any chance of being able to replace C++, so that the LLVMs and web browsers of the world can migrate incrementally. GCC was able to migrate from C to C++ because of this, and a migration from C++ to some other PL would need to work similarly.
> contemporary web browsers are unlikely to be fully rewritten in any other language
Right.
> it is an unreasonably high bar
It's not an unreasonable standard. We're talking about replacement. If isn't replacing C++ for this use case, then it's not a replacement by definition.
It's unreasonable in the sense that LLVM and a few others may survive even after pretty much everything else got replaced. We need to exempt some outliers with a very high sunk cost.
Yes, by that criteria C++ was successful over C. And C was successful over fortran. There are small communities that prefer the older stuff, but they were better enough to move the entire industry.
D isn't, and neither is Rust.
> I meant that D could have been in the position of Rust today if done right.
My point was Rust is just a completely different audience. I suppose D could have sold itself as a better JavaScript.
I think you're correct for D, but for Rust, we'll see. It's a very slow moving industry. I do C++ work all day (embedded) and while there's no current plans to move to Rust (which means it won't happen within the next 3-5 years), I could see it occurring someday.
We're finally (usually) allowed to use C++17. I had to use C++03 at times circa 2019 - we're finally done with that. It's _really_ slow moving.
> To be clear, I meant that D could have been in the position of Rust today if done right.
Exactly. One language died arguing about a feature (Dlang), two different languages, one without it (Rust), another with it (Golang) proved that it was not as significant.
