Guide should have a simple example on how to do inverse

[JelteF]

At the end of the generics section it makes a jump to traits because the generic function for inverse doesn't work right away. I think it would be useful to add a working version of a generic inverse at the end of the traits section. This doesn't leave readers wondering what would have to be done in the other case.

[steveklabnik]

I think this is a dup...

[elinorbgr]

In fact, this might be a little more tricky than expected. A simple implementation would be something like:

use std::num::{Zero, One};
use std::ops::Div;

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

    Ok(One::one() / x)
}

But it yields the error:

<anon>:7:8: 7:18 error: the type of this value must be known in this context
<anon>:7     Ok(One::one() / x)
                ^~~~~~~~~~

I believe it is the same situation as here: http://stackoverflow.com/a/26305660/2536143

[mvdnes]

The example can be fixed as follows:

use std::num::{Zero, One};
use std::ops::Div;

fn inverse<T: Div<T,T> + One + Zero>(x: T) -> Result<T, String> {
    if x.is_zero() { return Err("x cannot be zero!".to_string()); }

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

Using is_zero also eliminates the need for Eq.

[steveklabnik]

Closing as a dup of #17224