diff options
Diffstat (limited to '')
| -rw-r--r-- | library/alloc/src/collections/btree/node.rs | 28 |
1 files changed, 17 insertions, 11 deletions
diff --git a/library/alloc/src/collections/btree/node.rs b/library/alloc/src/collections/btree/node.rs index da766b67a..691246644 100644 --- a/library/alloc/src/collections/btree/node.rs +++ b/library/alloc/src/collections/btree/node.rs @@ -318,7 +318,10 @@ impl<BorrowType: marker::BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> pub fn ascend( self, ) -> Result<Handle<NodeRef<BorrowType, K, V, marker::Internal>, marker::Edge>, Self> { - let _ = BorrowType::TRAVERSAL_PERMIT; + const { + assert!(BorrowType::TRAVERSAL_PERMIT); + } + // We need to use raw pointers to nodes because, if BorrowType is marker::ValMut, // there might be outstanding mutable references to values that we must not invalidate. let leaf_ptr: *const _ = Self::as_leaf_ptr(&self); @@ -1003,7 +1006,10 @@ impl<BorrowType: marker::BorrowType, K, V> /// `edge.descend().ascend().unwrap()` and `node.ascend().unwrap().descend()` should /// both, upon success, do nothing. pub fn descend(self) -> NodeRef<BorrowType, K, V, marker::LeafOrInternal> { - let _ = BorrowType::TRAVERSAL_PERMIT; + const { + assert!(BorrowType::TRAVERSAL_PERMIT); + } + // We need to use raw pointers to nodes because, if BorrowType is // marker::ValMut, there might be outstanding mutable references to // values that we must not invalidate. There's no worry accessing the @@ -1666,17 +1672,17 @@ pub mod marker { pub struct ValMut<'a>(PhantomData<&'a mut ()>); pub trait BorrowType { - // If node references of this borrow type allow traversing to other - // nodes in the tree, this constant can be evaluated. Thus reading it - // serves as a compile-time assertion. - const TRAVERSAL_PERMIT: () = (); + /// If node references of this borrow type allow traversing to other + /// nodes in the tree, this constant is set to `true`. It can be used + /// for a compile-time assertion. + const TRAVERSAL_PERMIT: bool = true; } impl BorrowType for Owned { - // Reject evaluation, because traversal isn't needed. Instead traversal - // happens using the result of `borrow_mut`. - // By disabling traversal, and only creating new references to roots, - // we know that every reference of the `Owned` type is to a root node. - const TRAVERSAL_PERMIT: () = panic!(); + /// Reject traversal, because it isn't needed. Instead traversal + /// happens using the result of `borrow_mut`. + /// By disabling traversal, and only creating new references to roots, + /// we know that every reference of the `Owned` type is to a root node. + const TRAVERSAL_PERMIT: bool = false; } impl BorrowType for Dying {} impl<'a> BorrowType for Immut<'a> {} |