Panic and exceptions

By default, Zngur aborts the process if unwinding (Rust panic or C++ exception) reaches the cross-language boundary. Handling unwinding adds a non-zero performance cost to every function call and complicates things as catching unwinding can result in a corrupt state for some objects. (See unwind safety)

But Zngur has support for converting Rust panics into a C++ exception. To enable that, add

#convert_panic_to_exception

to your main.zng file. Now you can catch exceptions of kind rust::Panic for handling Rust panics:

try {
    std::cout << "s[2] = " << *s.get(2).unwrap() << std::endl;
    std::cout << "s[4] = " << *s.get(4).unwrap() << std::endl;
} catch (rust::Panic e) {
    std::cout << "Rust panic happened" << std::endl;
}

assuming s contains [2, 5, 7, 3], the above code prints:

s[2] = 7
thread '<unnamed>' panicked at 'called `Option::unwrap()` on a `None` value', examples/simple/src/generated.rs:184:39
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
s[4] = Rust panic happened

To disable the log, you need to register a panic hook on the Rust side (See this Stack Overflow question). Note that the rust::Panic object contains nothing, and you will lose the panic message.

For proper error handling, consider returning Result from your Rust functions and throw native C++ exceptions with proper details in case of an Err variant. Use this panic-to-exception mechanism only in places where you need catch_unwind in Rust (e.g. for increasing fault tolerance).