Comment by fluoridation
14 hours ago
>But you do have to think about it in the sense that every single line in your code could unwind.
No, this is actually just wrong. There is code that can throw, and there is code that cannot possibly throw. The way you write exception-safe code is by not holding manually-managed resources (e.g. raw pointers that own heap allocations, or file descriptors that must be close()d, or anything else that needs cleanup code that has not been put in a destructor) during sections that may throw. In other words, use RAII to manage your resources, regardless of whether exceptions may be thrown.
Program state is significantly more complex than just needing some RAII resources to cleanup via destructors.
> during sections that may throw
Yeah one of the problems with exceptions is it’s impossible to know what “may throw” other than “well I guess literally anything so everything”. It is very irritating.
At the end of the day exceptions are just a little syntactic sugar. Or perhaps syntactic bitters.
It is notable that systems languages designed after C++ all chose to not include exceptions. Go, Zig, Swift, Odin, Jai.
Rust panics are kinda sorta exceptions in that they unwind. But their intended use case is for irrecoverable errors. And of course you can set panic=abort.
C++ exceptions are very rarely treated as so serious module level irrecoverability.
>Program state is significantly more complex than just needing some RAII resources to cleanup via destructors.
You're being rather vague. All throwing does is cause control flow to jump to the nearest catch that can handle the exception, destructing all objects along the way. I struggle to think of an example that could cause problems that isn't some variation of "I had some code after the exception that I needed to run, and it didn't run, because it wasn't set up to run at scope exit". I'd love to see such an example if you have one.
>it’s impossible to know what “may throw”
* If it's a throw statement, it may throw.
* If it's an expression that contains a 'new' operator, it may throw.
* If it's an expression that contains a dynamic_cast to a reference type, it may throw.
* If it calls a function that you don't know that it does not do any of the above, it may throw.
* If it's unknown if a function is called (e.g. types are templated), it may throw.
* Otherwise, it doesn't throw.
If you're managing resources manually, either make sure not to call any functions until you release them, or stop managing them manually. I encourage the latter.
> You're being rather vague.
Completely forget about memory allocation and memory allocation like things.
Let’s say I have a physics system that runs an update. Assume we catch outside the update. If anything throws the system is now in an intermediate state and is effectively irrecoverable.
If you want to argue that exceptions should only be used for irrecoverable errors such that the subsystem is not expected to resume then I would list. This is akin to Rust panics which unwind like C++ exceptions but are not intended to resume. I have not read any comments in this large subthread arguing for using exceptions in this narrow style.
> it’s impossible to know what “may throw”
Yeah you’re just saying you should basically assume that any code can throw at any point. I think that’s a really really bad design pattern that makes code significantly harder to reason about. Control flow should be clear and obvious. “Any line of code could immediately unwind to unclear catch” is the objectively not clear and obvious.
But let me turn it around. You tell me an example of a system that doesn’t use exceptions where adding exceptions makes it better.
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