I’m still onboard with rust as being better than C, however…
My understanding is that it is considerably harder to correctly write unsafe rust than it is to correctly write c, because if you accidentally violate any of safe rust’s guaranteed invariants in an unsafe block, things go bananas.
Rust’s rules for valid unsafe code are not completely formalized yet. This means that there are open questions about whether particularly complex patterns in unsafe code will be guaranteed by future versions of the compiler to be sound. Conversely, the C and C++ spec are generally sufficient to determine whether any particular piece of code has undefined behavior, even if actually analyzing it to find out is not possible automatically using existing static analysis tools.
Because safe Rust is so strict about what it permits, the compiler is able to make more aggressive optimizations; in theory, this could indeed cause undefined behavior to be “worse” at runtime than a comparable situation in a globally-unsafe language. I’m unaware of any actual examples of that phenomenon, though.
Yes Rust is harder to write than C, that’s basically by design as it’s due to the statically guaranteed memory safety. That’s pretty magical. C doesn’t have that and neither does C++ even with smart pointers and such. Rusts unsafe keyword is poorly named, what it actually does is tell the compiler that you the programmer guarantee Rusts rules are upheld within the unsafe block.
For example
Access or modify a mutable static variable
That is a global, that’s incredibly hard to impossible to statically prove it’s safely done, so you have to do it in an unsafe block. So you violating Rusts rules within an unsafe block is actually using the unsafe block wrong. That’s not what it’s for
I remember watching a video of someone writing C code and making the same thing in unsafe rust. While the C code worked just fine the rust code had UB in it and was compiled to a different set of instructions.
Unsafe rust expects you to uphold the same guarantees that normal rust does and so the compiler will make all the same optimisations it would if the code wasn’t unsafe and this caused UB in the example rust code when optimised for performance. It worked just fine on the debug build, but that’s UB for you.
It is harder to write rust code than C code that the compiler will accept. It is IMHO easier to write rust code than to write correct C code, in the sense it only uses well defined constructs defined in the C standard.
The difference is that the rust compiler is much stricter, so you need to know a lot about details in the memory model, etc. to get your code past the compiler. In C you need the same knowledge to debug the program later.
I’m still onboard with rust as being better than C, however…
My understanding is that it is considerably harder to correctly write unsafe rust than it is to correctly write c, because if you accidentally violate any of safe rust’s guaranteed invariants in an unsafe block, things go bananas.
That’s true in C as well, though. This is what people mean when they say things like “undefined behavior can result in time travel”.
The difference is twofold:
unsafecode are not completely formalized yet. This means that there are open questions about whether particularly complex patterns in unsafe code will be guaranteed by future versions of the compiler to be sound. Conversely, the C and C++ spec are generally sufficient to determine whether any particular piece of code has undefined behavior, even if actually analyzing it to find out is not possible automatically using existing static analysis tools.Yes Rust is harder to write than C, that’s basically by design as it’s due to the statically guaranteed memory safety. That’s pretty magical. C doesn’t have that and neither does C++ even with smart pointers and such. Rusts unsafe keyword is poorly named, what it actually does is tell the compiler that you the programmer guarantee Rusts rules are upheld within the unsafe block.
For example
That is a global, that’s incredibly hard to impossible to statically prove it’s safely done, so you have to do it in an unsafe block. So you violating Rusts rules within an unsafe block is actually using the unsafe block wrong. That’s not what it’s for
I remember watching a video of someone writing C code and making the same thing in unsafe rust. While the C code worked just fine the rust code had UB in it and was compiled to a different set of instructions.
Unsafe rust expects you to uphold the same guarantees that normal rust does and so the compiler will make all the same optimisations it would if the code wasn’t unsafe and this caused UB in the example rust code when optimised for performance. It worked just fine on the debug build, but that’s UB for you.
That depends a lot on how you define “correct C”.
It is harder to write rust code than C code that the compiler will accept. It is IMHO easier to write rust code than to write correct C code, in the sense it only uses well defined constructs defined in the C standard.
The difference is that the rust compiler is much stricter, so you need to know a lot about details in the memory model, etc. to get your code past the compiler. In C you need the same knowledge to debug the program later.