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Implement PartialEq/Eq for SliceInfo #689

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Implement PartialEq/Eq for SliceInfo #689

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19 changes: 19 additions & 0 deletions src/slice.rs
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Expand Up @@ -295,6 +295,25 @@ pub struct SliceInfo<T: ?Sized, D: Dimension> {
indices: T,
}

impl<T1, D1, T2, D2> PartialEq<SliceInfo<T2, D2>> for SliceInfo<T1, D1>
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@jturner314 jturner314 Sep 4, 2019 •
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Why are D1 and D2 allowed to be different types? If D1 != D2, the SliceInfo instances are guaranteed to be unequal. I would think it would be more useful to catch that case at compile time instead of waiting until runtime.

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What if one is Dyn?

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Oh, right, I forgot that it's possible to create SliceInfo instances without using the s![] macro.

There's still some question in my mind, though, whether SliceInfo<T1, D1> and SliceInfo<T2, D2> should be considered equal (if their contents are equal) even if D1 and D2 are different. Both of these interpretations make sense to me:

  1. They should be equal because they will slice arrays in the same way (same indices and resulting shape).

  2. They should be unequal because the arrays resulting from slicing will have a different dimension types.

Since both interpretations make sense, I'd prefer to avoid the ambiguity by requiring D1 and D2 to be the same in the PartialEq impl. If someone wants to compare the contents of SliceInfo instances with different dimension types, they can just use info1.as_ref() == info2.as_ref().

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I wonder why we encourage this constant .as_ref() calling. ("This is not how conversion traits are supposed to be used, and it's fragile" is the short story).

We should add a method to them, if it's intended that you convert them like this in open code (not as part of converting function arguments).

where
T1: AsRef<[SliceOrIndex]>,
T2: AsRef<[SliceOrIndex]>,
D1: Dimension,
D2: Dimension,
{
fn eq(&self, other: &SliceInfo<T2, D2>) -> bool {
self.indices.as_ref() == other.indices.as_ref()
}
}

impl<T, D> Eq for SliceInfo<T, D>
where
T: AsRef<[SliceOrIndex]>,
D: Dimension,
{
}

impl<T: ?Sized, D> Deref for SliceInfo<T, D>
where
D: Dimension,
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