Improve hint for as_ref_mut

[Frosthage]

The hint for as_ref_mut was written before the function num_sq was added and is currently incorrect. I'm pretty sure you can improve this hint, but at least it's correct

[shadows-withal]

Suggested change

	Add AsRef<str> or AsMut<u32> as a trait bound to the functions."""
	Add AsRef<str> or AsMut<u32> as a trait bound to the functions as appropriate."""

[CaliViking]

Why would you limit the trait to u32? Shouldn't the trait allow any parameter that can be squared, so Mul trait? I know that the unit test specifies u32, but that seems pretty narrow, shouldn't the function support i32, i64, u32, u64, f32, f64?

[shadows-withal]

It's just as an example 🤷

[godmir]

You can actually make it generic, e.g.:

fn num_sq<T: AsMut<U> + AsRef<U>, U>(arg: &mut T) where U: Copy + MulAssign<U> {
    let x = *arg.as_ref();
    *arg.as_mut() *= x;
}

[Ttibsi]

Just realised this existed and went to put in my own PR instead (That I've now closed) - @Frosthage Instead of straight up adding the answer there (and also limiting it to a u32, like @CaliViking mentioned above), what if it had it's own hint saying something like "Consider the type you'd want to use" - I think it's already clear (ish) from the actual comments on that file that it wants to be T: AsMut<_> like the others are something like T: AsRef<str> and the hint just needs to steer the user towards the correct data type. I'm not sure what the data type we could hint towards should be - I used u32 in my own solution, but any numeric one would be fine (does this pass with a generic usize? I've not tested that)

[njr0]

FWIW, I just went through all the exercises (as a genuine newbie to Rust) and this was the only exercise I failed to complete properly (as far as I can tell), and I found the hint quite unhelpful.

I could fix it if I specialised num_sq to u32 (with or without the Box), but trying to do with with a combination of generic and Box seemed hard, especially since a lot of types don't implement multiplication. I'd love to see what a correct solution with the generic, handling the Box.

[0xVitalii]

Great improvement for sure!

[shadows-withal]

@all-contributors please add @Frosthage for content

[allcontributors]

@shadows-withal

I've put up a pull request to add @Frosthage! 🎉