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Clarify preconditions of raw size/align methods #103372

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Clarify preconditions of raw size/align methods #103372

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aa11214
Clarify preconditions of raw size/align methods
Jules-Bertholet Oct 21, 2022
fcbf7c4
Use @CAD97 's suggested wording
Jules-Bertholet Oct 22, 2022
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7 changes: 5 additions & 2 deletions library/core/src/alloc/layout.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -171,7 +171,9 @@ impl Layout {
///
/// # Safety
///
/// This function is only safe to call if the following conditions hold:
/// This function is safe to call if the pointer is safe to reborrow as `&T`
/// (in which case you could also call [`Layout::for_value`]). Otherwise,
/// the following conditions must hold:
///
/// - If `T` is `Sized`, this function is always safe to call.
/// - If the unsized tail of `T` is:
Expand All @@ -186,7 +188,8 @@ impl Layout {
/// call, but may panic or otherwise return the wrong value, as the
/// extern type's layout is not known. This is the same behavior as
/// [`Layout::for_value`] on a reference to an extern type tail.
/// - otherwise, it is conservatively not allowed to call this function.
/// - otherwise, it is conservatively allowed to call this function
/// only when it would be safe to reborrow `t` as a shared reference.
///
/// [trait object]: ../../book/ch17-02-trait-objects.html
/// [extern type]: ../../unstable-book/language-features/extern-types.html
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14 changes: 10 additions & 4 deletions library/core/src/mem/mod.rs
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Expand Up @@ -351,7 +351,9 @@ pub const fn size_of_val<T: ?Sized>(val: &T) -> usize {
///
/// # Safety
///
/// This function is only safe to call if the following conditions hold:
/// This function is safe to call if the pointer is safe to reborrow as `&T`
/// (in which case you could also call [`size_of_val`]). Otherwise, the
/// following conditions must hold:
///
/// - If `T` is `Sized`, this function is always safe to call.
/// - If the unsized tail of `T` is:
Expand All @@ -366,7 +368,8 @@ pub const fn size_of_val<T: ?Sized>(val: &T) -> usize {
/// call, but may panic or otherwise return the wrong value, as the
/// extern type's layout is not known. This is the same behavior as
/// [`size_of_val`] on a reference to a type with an extern type tail.
/// - otherwise, it is conservatively not allowed to call this function.
/// - otherwise, it is conservatively allowed to call this function
/// only when it would be safe to reborrow `val` as a shared reference.
///
/// [trait object]: ../../book/ch17-02-trait-objects.html
/// [extern type]: ../../unstable-book/language-features/extern-types.html
Expand Down Expand Up @@ -497,7 +500,9 @@ pub const fn align_of_val<T: ?Sized>(val: &T) -> usize {
///
/// # Safety
///
/// This function is only safe to call if the following conditions hold:
/// This function is safe to call if the pointer is safe to reborrow as `&T`
/// (in which case you could also call [`align_of_val`]). Otherwise, the
/// following conditions must hold:
///
/// - If `T` is `Sized`, this function is always safe to call.
/// - If the unsized tail of `T` is:
Expand All @@ -512,7 +517,8 @@ pub const fn align_of_val<T: ?Sized>(val: &T) -> usize {
/// call, but may panic or otherwise return the wrong value, as the
/// extern type's layout is not known. This is the same behavior as
/// [`align_of_val`] on a reference to a type with an extern type tail.
/// - otherwise, it is conservatively not allowed to call this function.
/// - otherwise, it is conservatively allowed to call this function
/// only when it would be safe to reborrow `val` as a shared reference.
///
/// [trait object]: ../../book/ch17-02-trait-objects.html
/// [extern type]: ../../unstable-book/language-features/extern-types.html
Expand Down