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assume_init: warn about valid != safe #63298

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Merged
merged 3 commits into from
Aug 6, 2019
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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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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
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Grammatical note: there are two possible interpretations with the comma here. If you change the comma to a semicolon ; or double dash --, is it the meaning you intended? If so, it will be better to change it. If not, it will be better to rephrase.

Another option is to drop the "this does not constitute a stable guarantee" part of the sentence because it is redundant with "under the current implementation".

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@Centril Centril Aug 6, 2019 •
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Another option is to drop the "this does not constitute a stable guarantee" part of the sentence because it is redundant with "under the current implementation".

It's not redundant; it is making the point that the current implementation is not a stable guarantee, but I'd rephrase as: "under the current implementation, which does not constitute a stable guarantee".

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@bluetech thanks! Turned it into a ;

/// 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:
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