Auto merge of #114795 - RalfJung:cell-swap, r=dtolnay · rust-lang/rust@f6faef4 (original) (raw)
`@@ -237,6 +237,7 @@
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`use crate::cmp::Ordering;
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`use crate::fmt::{self, Debug, Display};
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use crate::intrinsics::is_nonoverlapping;
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`use crate:📑:{PhantomData, Unsize};
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`use crate::mem;
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`use crate::ops::{CoerceUnsized, Deref, DerefMut, DispatchFromDyn};
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`@@ -415,6 +416,12 @@ impl Cell {
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`` /// Swaps the values of two Cells.
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`` /// Difference with std::mem::swap is that this function doesn't require &mut reference.
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`///
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/// # Panics
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///
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/// This function will panic if self and other are different Cells that partially overlap.
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/// (Using just standard library methods, it is impossible to create such partially overlapping Cells.
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/// However, unsafe code is allowed to e.g. create two &Cell<[i32; 2]> that partially overlap.)
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///
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`/// # Examples
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`///
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```` /// ```
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`@@ -430,14 +437,20 @@ impl Cell {
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`#[stable(feature = "move_cell", since = "1.17.0")]
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`pub fn swap(&self, other: &Self) {
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`if ptr::eq(self, other) {
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// Swapping wouldn't change anything.
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`return;
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`}
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if !is_nonoverlapping(self, other, 1) {
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// See https://github.com/rust-lang/rust/issues/80778 for why we need to stop here.
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panic!("Cell::swap on overlapping non-identical Cells");
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}
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`` // SAFETY: This can be risky if called from separate threads, but Cell
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`` // is !Sync so this won't happen. This also won't invalidate any
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`` // pointers since Cell makes sure nothing else will be pointing into
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// either of these Cells.
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// either of these Cells. We also excluded shenanigans like partially overlapping Cells,
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// so swap will just properly copy two full values of type T back and forth.
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`unsafe {
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`-
ptr::swap(self.value.get(), other.value.get());
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mem::swap(&mut *self.value.get(), &mut *other.value.get());
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`}
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`}
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``