I worked on two Rust projects over 500k LOC, one 800k LOC and one that's now at 1.5 million LOC.
Number one feature versus Kotlin, C++, C#, C, Haskell, Python, Ruby, etc. is how easy it is to refactor large-scale Rust code bases safely.
Refactoring a large C++ code-base is almost impossible to do correctly without introducing lots of bugs, undefined behavior, security vulnerabilities, etc.
We did a major refactor (completely parallelized an ~700k LOC application) in a relatively short span of time (6 months) in Rust without issues.
We are also not the only ones that did this. Mozilla tried to parallelize Firefox using C++, and this failed so hard, that they actually chose to develop Rust far enough first, to be able to do that in Rust instead, and all that work actually landed on Firefox a couple of years ago already. I wouldn't consider Firefox a "toy" project.
Number one feature versus Kotlin, C++, C#, C, Haskell, Python, Ruby, etc. is how easy it is to refactor large-scale Rust code bases safely.
Refactoring a large C++ code-base is almost impossible to do correctly without introducing lots of bugs, undefined behavior, security vulnerabilities, etc.
We did a major refactor (completely parallelized an ~700k LOC application) in a relatively short span of time (6 months) in Rust without issues.
We are also not the only ones that did this. Mozilla tried to parallelize Firefox using C++, and this failed so hard, that they actually chose to develop Rust far enough first, to be able to do that in Rust instead, and all that work actually landed on Firefox a couple of years ago already. I wouldn't consider Firefox a "toy" project.