Update control_flow.rs

Fix and extent ControlFlow `traverse_inorder` example 1. The existing example compiles on its own, but any usage fails to be monomorphised and so doesn't compile. Fix that by using Fn trait instead of FnMut. 2. Added an example usage of `traverse_inorder` showing how we can terminate the traversal early. Fixes #90063
rust-lang · bors · Oct 26, 2021 · Oct 11, 2021 · Oct 23, 2021 · Oct 23, 2021
commit 508fadab16ec36c57daa8f0361db60848d31c0f7
diff --git a/library/core/src/ops/control_flow.rs b/library/core/src/ops/control_flow.rs
@@ -34,17 +34,40 @@ use crate::{convert, ops};
 /// }
 ///
 /// impl<T> TreeNode<T> {
-///     pub fn traverse_inorder<B>(&self, mut f: impl FnMut(&T) -> ControlFlow<B>) -> ControlFlow<B> {
+///     pub fn traverse_inorder<B>(&self, f: &impl Fn(&T) -> ControlFlow<B>) -> ControlFlow<B> {
 ///         if let Some(left) = &self.left {
-///             left.traverse_inorder(&mut f)?;
+///             left.traverse_inorder(f)?;
 ///         }
 ///         f(&self.value)?;
 ///         if let Some(right) = &self.right {
-///             right.traverse_inorder(&mut f)?;
+///             right.traverse_inorder(f)?;
 ///         }
 ///         ControlFlow::Continue(())
 ///     }
 /// }
+///
+/// let node = TreeNode {
+///     value: 0,
+///     left: Some(Box::new(TreeNode {
+///         value: 1,
+///         left: None,
+///         right: None
+///     })),
+///     right: Some(Box::new(TreeNode {
+///         value: 2,
+///         left: None,
+///         right: None
+///     }))
+/// };
+///
+/// node.traverse_inorder(& |val| {
+///     println!("{}", val);
+///     if *val <= 0 {
+///         ControlFlow::Break(())
+///     } else {
+///         ControlFlow::Continue(())
+///     }
+/// });
 /// ```
 #[stable(feature = "control_flow_enum_type", since = "1.55.0")]
 #[derive(Debug, Clone, Copy, PartialEq)]