# Macro core::panic
1.6.0[−][src]

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

Expand description

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

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