Move util::linked_list to layout

components/layout/linked_list.rs

@@ -0,0 +1,21 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Utility functions for doubly-linked lists.
+
+use std::collections::LinkedList;
+use std::mem;
+
+/// Splits the head off a list in O(1) time, and returns the head.
+pub fn split_off_head<T>(list: &mut LinkedList<T>) -> LinkedList<T> {
+    let tail = list.split_off(1);
+    mem::replace(list, tail)
+}
+
+/// Prepends the items in the other list to this one, leaving the other list empty.
+#[inline]
+pub fn prepend_from<T>(this: &mut LinkedList<T>, other: &mut LinkedList<T>) {
+    other.append(this);
+    mem::swap(this, other);
+}