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assume_init: warn about valid != safe #63298

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Merged
merged 3 commits into from
Aug 6, 2019
Merged

assume_init: warn about valid != safe #63298

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assume_init: warn about valid != safe
RalfJung Aug 5, 2019
1b9eb4a
be clear that 1-init Vec being valid (but not safe) is not a stable g…
RalfJung Aug 6, 2019
1821414
clarify
RalfJung Aug 6, 2019
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11 changes: 10 additions & 1 deletion src/libcore/mem/maybe_uninit.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -51,7 +51,8 @@ use crate::mem::ManuallyDrop;
///
/// On top of that, remember that most types have additional invariants beyond merely
/// being considered initialized at the type level. For example, a `1`-initialized [`Vec<T>`]
/// is considered initialized because the only requirement the compiler knows about it
/// is considered initialized (under the current implementation; this does not constitute
/// a stable guarantee) because the only requirement the compiler knows about it
/// is that the data pointer must be non-null. Creating such a `Vec<T>` does not cause
/// *immediate* undefined behavior, but will cause undefined behavior with most
/// safe operations (including dropping it).
Expand Down Expand Up @@ -402,6 +403,14 @@ impl<T> MaybeUninit<T> {
///
/// [inv]: #initialization-invariant
///
/// On top of that, remember that most types have additional invariants beyond merely
/// being considered initialized at the type level. For example, a `1`-initialized [`Vec<T>`]
/// is considered initialized (under the current implementation; this does not constitute
/// a stable guarantee) because the only requirement the compiler knows about it
/// is that the data pointer must be non-null. Creating such a `Vec<T>` does not cause
/// *immediate* undefined behavior, but will cause undefined behavior with most
/// safe operations (including dropping it).
///
/// # Examples
///
/// Correct usage of this method:
Expand Down