Macro core::panic

macro_rules! panic {
    ($($arg : tt) *) => { ... };
}

Panics the current thread.

This allows a program to terminate immediately and provide feedback to the caller of the program. panic! should be used when a program reaches an unrecoverable state.

This macro is the perfect way to assert conditions in example code and in tests. panic! is closely tied with the unwrap method of both Option and Result enums. Both implementations call panic! when they are set to None or Err variants.

When using panic!() you can specify a string payload, that is built using the format! syntax. That payload is used when injecting the panic into the calling Rust thread, causing the thread to panic entirely.

The behavior of the default std hook, i.e. the code that runs directly after the panic is invoked, is to print the message payload to stderr along with the file/line/column information of the panic!() call. You can override the panic hook using std::panic::set_hook(). Inside the hook a panic can be accessed as a &dyn Any + Send, which contains either a &str or String for regular panic!() invocations. To panic with a value of another other type, panic_any can be used.

Result enum is often a better solution for recovering from errors than using the panic! macro. This macro should be used to avoid proceeding using incorrect values, such as from external sources. Detailed information about error handling is found in the book.

See also the macro compile_error!, for raising errors during compilation.

Current implementation

If the main thread panics it will terminate all your threads and end your program with code 101.

Examples

panic!();
panic!("this is a terrible mistake!");
panic!("this is a {} {message}", "fancy", message = "message");
std::panic::panic_any(4); // panic with the value of 4 to be collected elsewhere