Function catch_unwind

pub fn catch_unwind<F: FnOnce() -> R + UnwindSafe, R>(f: F) -> Result<R>

Invokes a closure, capturing the cause of an unwinding panic if one occurs.

This function will return Ok with the closure’s result if the closure does not panic, and will return Err(cause) if the closure panics. The cause returned is the object with which panic was originally invoked.

It is currently undefined behavior to unwind from Rust code into foreign code, so this function is particularly useful when Rust is called from another language (normally C). This can run arbitrary Rust code, capturing a panic and allowing a graceful handling of the error.

It is not recommended to use this function for a general try/catch mechanism. The Result type is more appropriate to use for functions that can fail on a regular basis. Additionally, this function is not guaranteed to catch all panics, see the “Notes” section below.

The closure provided is required to adhere to the UnwindSafe trait to ensure that all captured variables are safe to cross this boundary. The purpose of this bound is to encode the concept of exception safety in the type system. Most usage of this function should not need to worry about this bound as programs are naturally unwind safe without unsafe code. If it becomes a problem the AssertUnwindSafe wrapper struct can be used to quickly assert that the usage here is indeed unwind safe.

Notes

Note that this function might not catch all panics in Rust. A panic in Rust is not always implemented via unwinding, but can be implemented by aborting the process as well. This function only catches unwinding panics, not those that abort the process.

Note that if a custom panic hook has been set, it will be invoked before the panic is caught, before unwinding.

Also note that unwinding into Rust code with a foreign exception (e.g. an exception thrown from C++ code) is undefined behavior.

Finally, be careful in how you drop the result of this function. If it is Err, it contains the panic payload, and dropping that may in turn panic!

Examples

use std::panic;

let result = panic::catch_unwind(|| {
    println!("hello!");
});
assert!(result.is_ok());

let result = panic::catch_unwind(|| {
    panic!("oh no!");
});
assert!(result.is_err());