For non-rusties: unsafe means turning off Rust's advanced safety features, reducing its safety level to that of C or C++. Which is to say, it's as safe as almost all software you're using right now. Of course, one usually turns off the safety features because one is trying to do something tricky to squeeze out performance or achieve some low level feat, so it's also an indicator that something is dangerous is going on.
In your C++ you might add a comment explaining the behaviour you're relying on to convince any reader of the correctness of your code. The cool thing about Rust is that anywhere you don't have the unsafe block, you're (theoretically) certain there's no tricky business going on without even having to read the code.
There was a lot of commotion in the community because many rustaceans take a lot of pride in having this safety features. They took offense at disabling those features, risking Rust's reputation of safety, for seemingly meaningless goals (such as winning the TechEmpower benchmarks). It's not disabling the safety features that makes the code faster btw, it's the tricks you're allowed to do when the safety is off that might yield performance improvements.
> For non-rusties: unsafe means turning off Rust's advanced safety features, reducing its safety level to that of C or C++.
Actually, it's a bit more subtle: unsafe allows using some things which are not protected by "Rust's advanced safety features", like dereferencing raw pointers, and using these things can "reduce its safety level to that of C or C++" (for that module). However, if these things are not used, the safety is not reduced; you can take a block of Rust code which has no "unsafe", put it in an "unsafe" block, and it will be identically safe as before.
In your C++ you might add a comment explaining the behaviour you're relying on to convince any reader of the correctness of your code. The cool thing about Rust is that anywhere you don't have the unsafe block, you're (theoretically) certain there's no tricky business going on without even having to read the code.
There was a lot of commotion in the community because many rustaceans take a lot of pride in having this safety features. They took offense at disabling those features, risking Rust's reputation of safety, for seemingly meaningless goals (such as winning the TechEmpower benchmarks). It's not disabling the safety features that makes the code faster btw, it's the tricks you're allowed to do when the safety is off that might yield performance improvements.