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It's beginning to get tiresome to continually hear the Rust community go on and on about how amazing Rust is and say, with a straight face, that eventually there will be no reason to write anything in not-Rust. Are you serious? The hubris is off the charts.So a few considerations here: (1) I really have no connection with the Rust community aside from curiosity, so it's quite dishonest to project my opinion onto all of them, and (2) this is very much my personal opinion.
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I'd still defend the position though. Every language has merits, but especially for a lot of the older ones, there are so many accumulated problems that it's worth considering newer languages just because they're learned so much for the mistakes of their predecessors. For example, I've been doing Ruby for quite a few years now:
* Having so few constraints on implementation (e.g. duck typing) was an interesting concept, but time has proven it to be a nightmare maintainability. It buys you a little early productivity, but any honest person with a huge Ruby codebase can tell you that it's a liability.
* The only way to get truly good performance is to write a C extension. The language's whole implementation and performance-sensitive libraries are all C. Contrast this to modern languages where it's an embarrassment if your compiler is _not_ written in the language itself (Rust, Go, Swift, etc.).
* Core build infrastructure (Bundler) and environment management (rbenv) is maintained separately from the language. It works fine, but the reason it's not more core is not because it's better that way, but because the language's original designers didn't realize they'd be necessary, so they had to be developed separately. This has the effect of making the whole toolchain complex and hard for beginners to understand because none of it is integrated.
* The interpreter starts out faster than a compiler, but it breaks down fast. Codebases in the 100,000s of lines or more will take on the order of 10-100 seconds to start up, and the only way to get back to a fast edit-compile-debug loop is through tricks like Zeus. After you resort to that, unreliable runs and weird loading problems become a part of common life.
These aren't small problems. Also, I'm picking on Ruby here, but you could drill into a lot of existing languages and find flaws that are roughly on this level (JS/Python/C++/Erlang are easy, but even fan favorites like Haskell and Scala have pretty serious ones). Newer languages have their problems too, but rarely anything on this sort of existential scale.
We should stop pretending that all languages are equal with their own share of upsides and downsides. Given decades of language building, it would be disappointing if lessons hadn't been learned. Luckily this isn't the case.
In terms of what we write new projects in given a few years, there are other good contenders, but like I said above, I think that Rust has nailed a performance/safety/productivity/ecosystem compromise that's quite a bit above and beyond most of anything else.