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choppsv1 opened this issue Mar 25, 2025 · 1 comment · Fixed by #493
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Question on variance text #483

choppsv1 opened this issue Mar 25, 2025 · 1 comment · Fixed by #493

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@choppsv1
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choppsv1 commented Mar 25, 2025 •
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I'm reading through the subtyping and variance chapter and the following text confused me:

Also, we saw that it was not ok for us to treat
`&mut &'a U` as a subtype of `&mut &'b U`,
therefore we can say that `&mut T` is *invariant* over `T`

Why is U introduced in the premise here and then not used in the conclusion? Shouldn't the premise just use T again, or if for some reason no, shouldn't the conclusion at least use U?
@senekor
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senekor commented May 22, 2025

Yeah, I think there's no reason for that. Using T consistently would be more appropriate.

@senekor senekor mentioned this issue May 22, 2025
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Use consistent type parameters in subtyping.md senekor/nomicon
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@choppsv1 @senekor