Guide: Fixing Inverse in Generics section

[prakhar1989]

In the section on Generics, the inverse function is introduced which gives inverse of a f32 and f64. The section uses this following code to demonstrate the usage of Traits but then doesn't provide an example of how to fix the original problem.

fn inverse<T>(x: T) -> Result<T, String> {
    if x == 0.0 { return Err("x cannot be zero!".to_string()); }

    Ok(1.0 / x)
}

As a beginner, I found it a bit hard to make this work as the solution is quite unintuitive for someone new to rust.

fn inverse<T: Float>(x: T) -> Result<T, String> {
    // converting slice to String
    let f0: T = std::num::Zero::zero();
    let f1: T = std::num::One::one();
    if x == f0 { return Err("x cannot be zero!".to_string()); }
    Ok(f1 / x)
}

It would be great if after the diversion to Traits the generics section closes off with a solution to the inverse problem with a bit of explanation of std::num module.

[huonw]

cc @steveklabnik

(BTW, your replacement code can use std::num::one and call .is_zero, i.e.

fn inverse<T: Float>(x: T) -> Result<T, &'static str> {
    if x.is_zero() { return Err("x cannot be zero!") }

    Ok(std::num::one::<T>() / x)
}

Not super important of course.)

[prakhar1989]

Thanks @huonw 👍

[steveklabnik]

Is this still the way to go with the changes to std::num?