Use &mut [MaybeUninit<T>] in iter::collect
#852
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We create a mutable slice to the uninitialized tail when collecting into a `Vec<T>`, but the Rust Reference says it's UB to produce "a reference or `Box<T>` that is dangling, unaligned, or points to an invalid value." [UCG#77] hasn't resolved the validity of references to uninitialized data yet, but we can avoid it by using `MaybeUninit<T>`. [UCG#77]: rust-lang/unsafe-code-guidelines#77
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nikomatsakis
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We create a mutable slice to the uninitialized tail when collecting into
a
Vec<T>, but the Rust Reference says it's UB to produce "a referenceor
Box<T>that is dangling, unaligned, or points to an invalid value."UCG#77 hasn't resolved the validity of references to uninitialized
data yet, but we can avoid it by using
MaybeUninit<T>.Fixes #851.