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btree: safety comments for init and new #146785

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Merged
merged 1 commit into from
Sep 20, 2025
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btree: safety comments for init and new #146785

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8 changes: 7 additions & 1 deletion library/alloc/src/collections/btree/node.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -67,6 +67,10 @@ struct LeafNode<K, V> {

impl<K, V> LeafNode<K, V> {
/// Initializes a new `LeafNode` in-place.
///
/// # Safety
///
/// The caller must ensure that `this` points to a (possibly uninitialized) `LeafNode`
unsafe fn init(this: *mut Self) {
// As a general policy, we leave fields uninitialized if they can be, as this should
// be both slightly faster and easier to track in Valgrind.
Expand All @@ -79,9 +83,11 @@ impl<K, V> LeafNode<K, V> {

/// Creates a new boxed `LeafNode`.
fn new<A: Allocator + Clone>(alloc: A) -> Box<Self, A> {
let mut leaf = Box::new_uninit_in(alloc);
unsafe {
let mut leaf = Box::new_uninit_in(alloc);
// SAFETY: `leaf` points to a `LeafNode`
LeafNode::init(leaf.as_mut_ptr());
// SAFETY: `leaf` was just initialized
leaf.assume_init()
}
}
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