Batman

Have you ever written a function like this that was hard to debug?

fn main() {
    let signal = [""; 16].join(&format!("{}", f64::sqrt(50.3 - 50.0 - 0.3)));

    println!("{signal} Batman!");
}

Well now you don't have to be confused any more! Just let batman configure FPU hardware exceptions and your days of debugging garbage floating point calculations will be over!

fn main() {
    // Here be dragons!
    unsafe { batman::signal() };

    let signal = [""; 16].join(&format!("{}", f64::sqrt(50.3 - 50.0 - 0.3)));

    println!("{signal} Batman!");
}

Let's see how it works:

$ cargo run --example batman
    Finished dev [unoptimized + debuginfo] target(s) in 0.00s
     Running `target/debug/examples/batman`
Caught signal 8 (SIGFPE): Floating point exception
   0: batman::backtrace::Backtrace::new
             at ./src/backtrace.rs:14:20
   1: batman::unix::sigfpe_handler
             at ./src/unix.rs:25:14
   2: <unknown>
   3: std::f64::<impl f64>::sqrt
             at /rustc/9ad5d82f822b3cb67637f11be2e65c5662b66ec0/library/std/src/f64.rs:345
   4: batman::main
             at ./examples/batman.rs:5:47
   5: core::ops::function::FnOnce::call_once
             at /rustc/9ad5d82f822b3cb67637f11be2e65c5662b66ec0/library/core/src/ops/function.rs:227:5

Aborted

Signal SIGFPE is caught on line 5 in batman.rs in the call to f64::sqrt()! Multiply this by several thousand lines of various linear algebra calculations used in games and scientific computing, and batman will have your back.

But floating point exceptions are slow and they crash my program!

That's why batman only enables them when debug assertions are enabled.

$ cargo run --example batman --release
    Finished release [optimized] target(s) in 0.00s
     Running `target/release/examples/batman`
NaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaN Batman!

But setting signal and exception handlers mutates global state!

Yeah, configuring FPU exceptions was made unsafe because this can be a real problem. On the bright side, enabling exceptions themselves is thread-local state, so you can decide to raise exceptions on a per-thread basis. But be aware that threads inherit FPU exceptions from their parent, and there is no way to turn it off (for API simplicity).

Caveats

batman requires unstable features and only works on nightly compilers. Since you're obviously adventurous anyway, you can use it on stable with nightly-crimes.

Why is it named batman?

If the joke wasn't clear by now, I humbly refer you to https://www.destroyallsoftware.com/talks/wat. Combine this with the bat signal implication, and you'll agree it's the best name.