Using Or mutably - query violates a unique borrow about hecs

[junglie85]

Ah, you're very right re Or. I understand now why the error is being raised - my query satisfies both L and R so we have two mutable borrows of the same data, which cannot happen.

I originally tried the &Option<Input> and it didn't work, which is why I reached for Or. Thanks for your example - I had the borrow in the wrong place!

[Ralith]

This should work, but it looks like there's a bug here; thanks for the report! In the mean time, what you probably want to do is use the query (&mut Transform, &Physics, &Drawable, Option<&Input>) anyway, which will definitely work.

[Ralith]

On closer review, this is working as intended. Or is documented as:

Holds an L, or an R, or both

When an entity satisfies both, you get both. Two &mut Transforms to the same value would be illegal aliasing. If both clasues of an Or contain the same &mut T, you need to ensure that no entity will ever match both. In your case you should use an Option instead, so that the common references aren't needlessly duplicated.