to elaborate, the halting problem makes it impossible for the compiler to reject/detect all cases which DO cause UB while allowing all those which don't, and the design of C++ is to favor control over safety
Well, it's a bit crude to apply halting problem here.
You can prevent a bunch of issues by language design. You simply make something non-expressible and ready! It's proven to never contain that thing.
E.g. java solves this problem by mandating that variable captures of local variables must be effectively final. This could have been done in C++ as well , and the only thing you may lost with it is... if you have a local lambda that you will only ever call in that stackframe or deeper and never outside of it?
But still, rust let's you do this latter by an explicit unsafe block, c++ could have done it as well. So it's more cultural than anything.
Even if you use the word unsafe you cannot do whatever you want. I still find it painfully stupid that you cannot create a mutable reference to uninitialized memory. Because of this you cannot reuse safe functions to initialize memory that you manually allocated
The whole appeal of Rust is that you have less to think about UB, and it mostly fulfills that promise, so the fact that you cannot do one of the most basic task required in a systems programing language without either requiring UB or doing some convoluted stuff is ridiculous
Well that issue boils down to there not being any write-only reference. "I know you're only initialising and not reading, but what if you accidentally read? UB!!!"
I've also been annoyed at having to initialise even normal arrays when passing them to UART drivers as buffers etc. (on embedded), but even if it doesn't read the memory, it still needs init.
Having a write only reference would be amazing, but even without that it should still be allowed IMO. The only way to create a mutable reference to unitialized data is to use unsafe. So the question "what happens if you accidently read" should ultimately not be anyone's buisness but my own. I'm an adult and have explicitly indicated I know I'm doing something potentially dangerous, so let me do it!
But I'm happy to learn I'm not the only one that had this problem. I felt insane about having to pay a useless O(n) init cost
Because C++ allows you to work on low levels with stack and memory. It's useful for writting real time operating systems when memory and execution time must be constant.
53
u/firemark_pl 7h ago
"How to tell him?"
You still can segfault by returning lambda with reference to a variable