That would have been too limiting since there are many (e.g. C) functions that can never throw but are not marked noexcept. Not being able to mark your function noexcept just because you call some standard math function would be counterproductive.
There were ways around this. C functions in the standard library could easily be marked noexcept, for one. Extern C could also imply noexcept. Also, explicit try/catch blocks could be required when calling a potentially-throwing function from a noexcept function - slightly annoying, but not a huge problem in practice.
Overall this was just another case of the C++ community's preference for speed over safety and robustness. Nothing new, but still a shame to see that the attitude hasn't changed at all.
> There were ways around this. C functions in the standard library could easily be marked noexcept, for one.
C++ standard library function yes, C standard library functions, incloding those imported into C++ are more complicated since on most platforms those are not provided by the C++ implementation but some other lower level library. Third-party libraries are the bigger concern though.
> Extern C could also imply noexcept.
In theory this might be correct but in practice this will cause problems with C functions that take callbacks which the user might want to throw from. These are already problematic especially since the C code won't unwind anything but you'd still need to concern yourself with potentially breaking user code.
> Also, explicit try/catch blocks could be required when calling a potentially-throwing function from a noexcept function - slightly annoying, but not a huge problem in practice.
Yes, but avoiding that is the whole point. The try-cach for potentially when you call potentially throwing functions is already implicitly provided by current noexcept and if your noexcept function only calls only noexcept functions then the compiler can already elide all that.
> Overall this was just another case of the C++ community's preference for speed over safety and robustness.
Not at all. If that was the case then noexcept would only be a compiler hint and exceptions bubbling up to noexcept functions would be undefined behavior. Arguably that would be better than what we have now.
> C++ standard library function yes, C standard library functions, incloding those imported into C++ are more complicated since on most platforms those are not provided by the C++ implementation but some other lower level library. Third-party libraries are the bigger concern though.
Since noexcept is a compilation-level hint, it only matters that the declaration contains them in the <cstdXX> headers, not who provides the implementations. And since C functions can't deal with exceptions thrown from callbacks, it would make sense to annotate any function pointer that you provide with noexcept as well.
> Yes, but avoiding that is the whole point. The try-cach for potentially when you call potentially throwing functions is already implicitly provided by current noexcept and if your noexcept function only calls only noexcept functions then the compiler can already elide all that.
The current implementation calls std::terminate() if an exception is caught. That needn't be the case in practice: you could well handle the exception in a meaningful way and continue execution. Also, having the programmer explicitly do this is valuable in itself, even if they also just call std::terminate(). For example, with the way noexcept is implemented today, you have no notification if a function you're calling goes from noexcept to potentially throwing until your program actually crashes. If noexcept was an actual compiler-checked keyword, your code would stop compiling if one of the functions you rely on started throwing exceptions, and you could decide what to do (maybe catch it, maybe find an alternative, etc).
> Not at all. If that was the case then noexcept would only be a compiler hint and exceptions bubbling up to noexcept functions would be undefined behavior. Arguably that would be better than what we have now.
Crashing the program is of course better than UB. But it's still the worse possible thing to happen other than that. It basically makes noexcept functions be the most scary functions to ever call, instead of being the safest. And if you want to write a piece of code that can never throw an exception, the compiler still won't help you in any way to do that, it's up to you to do it correctly or crash.
