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Doc-comment IndexVec::from_elem and use it in a few more places

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Scott McMurray 2023-04-03 14:22:09 -07:00
parent bf41e753ec
commit 5c3e5af2ed
5 changed files with 17 additions and 7 deletions
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11
compiler/rustc_index/src/vec.rs
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@ -129,6 +129,17 @@ impl<I: Idx, T> IndexVec<I, T> {
IndexVec { raw: Vec::with_capacity(capacity), _marker: PhantomData }
}
/// Creates a new vector with a copy of `elem` for each index in `universe`.
///
/// Thus `IndexVec::from_elem(elem, &universe)` is equivalent to
/// `IndexVec::<I, _>::from_elem_n(elem, universe.len())`. That can help
/// type inference as it ensures that the resulting vector uses the same
/// index type as `universe`, rather than something potentially surprising.
///
/// For example, if you want to store data for each local in a MIR body,
/// using `let mut uses = IndexVec::from_elem(vec![], &body.local_decls);`
/// ensures that `uses` is an `IndexVec<Local, _>`, and thus can give
/// better error messages later if one accidentally mismatches indices.
#[inline]
pub fn from_elem<S>(elem: T, universe: &IndexSlice<I, S>) -> Self
where