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

1 files changed, 26 insertions, 3 deletions

diff --git a/library/core/src/ops/control_flow.rs b/library/core/src/ops/control_flow.rs
index cd2d57699c9..ec00d0fe05b 100644
--- 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)]