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doc: explain why it is unsafe to construct Vec<u8> from Vec<u16> #65873

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Oct 28, 2019
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doc: explain why it is unsafe to construct Vec<u8> from Vec<u16> #65873

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6 changes: 5 additions & 1 deletion src/liballoc/vec.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -411,7 +411,11 @@ impl<T> Vec<T> {
///
/// Violating these may cause problems like corrupting the allocator's
/// internal data structures. For example it is **not** safe
/// to build a `Vec<u8>` from a pointer to a C `char` array and a `size_t`.
/// to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`.
/// It's also not safe to build one from a `Vec<u16>` and its length, because
/// the allocator cares about the alignment, and these two types have different
/// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
/// turning it into a `Vec<u8>` it'll be deallocated with alignment 1.
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This reads just a little off; I would say

    /// to build a `Vec<u8>` from a pointer to a C `char` array with length `size_t`.
    /// It's also not safe to build one from a `Vec<u16>` and its length, because 
    /// the allocator cares about the alignment, and these two types have different 
    /// alignments. The buffer was allocated with alignment 2 (for `u16`), but after
    /// turning it into a `Vec<u8>` it'll be deallocated with alignment 1.

///
/// The ownership of `ptr` is effectively transferred to the
/// `Vec<T>` which may then deallocate, reallocate or change the
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