A ban on C++ exceptions is a huge red flag for me. A project has to be really special if I'm going to contribute to it after it's crippled the language.
void read_file_by_lines(const char* path, void (*callback)(const char* line)) {
FILE* file = fopen(path, "r");
size_t length = 0;
char* line = NULL;
while (-1 != getline(&line, &length, file)) {
callback(line);
}
free(line);
fclose(file);
}
C++ exceptions are predicated on the assumption that all resources are managed using RAII. In the real world, this isn't true, especially considering that C doesn't even have RAII.
Python programmers (including me) love their exceptions, because Python is a dynamic language, and exposes system resources as reference counted objects.
The most general definition of the restriction is that C++ code cannot throw exceptions through exception unsafe code. How do you know if your C++ function was called from exception unsafe code? You can't!
So it's only ever safe to throw an exception when you are expecting it to be caught immediately i.e. you can use exceptions as glorified error codes, but not much else.
In Django I can throw a Http404 exception from deep inside a view and the server will come up with a 404 response. I can assert and the client will get a 500 error but the server won't go down. This is the real power of exceptions, and God help anybody who tries to do it in C++.
In the enterprise context you can hardly count on proper documentation, specially in projects with high attrition of consultants where each one comes, implements something and departures to the next gig.
Not to count the commercial libraries distributed in binary only form.
So one never knows if the code is exception safe, don't work with exceptions or is exception happy.
I think there are examples related to inter-library exceptions that might be much more subtle than this one, but I've never understood the subtlety.
C++ users in particular have strong concerns about things like RTTI and the overhead of exceptions not thrown. The cost of making unthrown exceptions low (near zero) is that throwing exceptions is much more expensive. This turns into a feedback loop, where C++ programs end up performing better if they never throw any exceptions because of the tradeoff.
This feeds into self-hosted compilers. Thing is, certain compiler design techniques can work well with cheap unwinding: constraint solving (more common in languages with better type systems than C++), forward-looking grammar assertions with speculative parsing, IDE-integrated code completion (implement the lexer to add the cursor position as a special token, and jump out of the parser when it's found, where all the context is available to pass along). But C++'s peculiar tradeoffs may make using things like exceptions less than ideal to use for this purpose, not because exceptions are the wrong tool, but because most C++ programs are not compilers and aren't tuned for it.
And OTOH, compilers written in low-level languages like C++ often twist themselves into knots to simulate things like tree pattern matching, multiple dispatch, destructuring binds, etc. Sometimes they even give up and write code generating tools.
So by having exceptions, with code that only knows about C semantics but was compiled with C++ mode, you open the door to all sorts of nasty surprises.
So exceptions can cause resource leaks and other issues like being thrown in the middle of a UNIX signal.
Which leads to the situation that sadly many library writers avoid them.
I still enjoy using C++, but the best place for it is as infrastructure language for the bottom layer when performance requires it, then using something else on the other layers.