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Avoid excessive reallocations during item-bodies checking #31929

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Feb 27, 2016
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Avoid excessive reallocations during item-bodies checking #31929

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5 changes: 5 additions & 0 deletions src/librustc/middle/subst.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -555,6 +555,11 @@ impl<'a,T> Iterator for EnumeratedItems<'a,T> {
None
}
}

fn size_hint(&self) -> (usize, Option<usize>) {
let size = self.vec.as_slice().len();
(size, Some(size))
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This overestimates the number of elements in the iterator, doesn't it?

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No, it doesn't. The underlying vector is used in its entirety. If you check VecPerParamSpace::limits() one can see how it is split into three consecutive ranges.

(We discussed this on IRC, I'm just adding this comment for reference.)

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I now understand the iterator! It's fine. We cleared this up on irc.

}
}

impl<T> IntoIterator for VecPerParamSpace<T> {
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