diff --git a/library/alloc/src/collections/btree/node.rs b/library/alloc/src/collections/btree/node.rs index d831161bcb6..f1d2d3b30d9 100644 --- a/library/alloc/src/collections/btree/node.rs +++ b/library/alloc/src/collections/btree/node.rs @@ -318,7 +318,7 @@ impl NodeRef pub fn ascend( self, ) -> Result, marker::Edge>, Self> { - assert!(BorrowType::PERMITS_TRAVERSAL); + let _ = 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 +1003,7 @@ impl /// `edge.descend().ascend().unwrap()` and `node.ascend().unwrap().descend()` should /// both, upon success, do nothing. pub fn descend(self) -> NodeRef { - assert!(BorrowType::PERMITS_TRAVERSAL); + let _ = 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 @@ -1666,15 +1666,17 @@ pub mod marker { pub struct ValMut<'a>(PhantomData<&'a mut ()>); pub trait BorrowType { - // Whether node references of this borrow type allow traversing - // to other nodes in the tree. - const PERMITS_TRAVERSAL: bool = true; + // 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: () = (); } impl BorrowType for Owned { - // Traversal isn't needed, it happens using the result of `borrow_mut`. + // 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 PERMITS_TRAVERSAL: bool = false; + const TRAVERSAL_PERMIT: () = panic!(); } impl BorrowType for Dying {} impl<'a> BorrowType for Immut<'a> {}