Use ops::ControlFlow in graph::iterate

Author: scottmcm

core/src/iter/adapters/mod.rs

@@ -1273,7 +1273,7 @@ where
         ) -> impl FnMut((), T) -> ControlFlow<(), B> + '_ {
             move |(), x| match f(x) {
                 Some(x) => ControlFlow::Break(x),
-                None => ControlFlow::Continue(()),
+                None => ControlFlow::CONTINUE,
             }
         }
 

core/src/iter/traits/double_ended.rs

@@ -310,7 +310,7 @@ pub trait DoubleEndedIterator: Iterator {
             mut predicate: impl FnMut(&T) -> bool,
         ) -> impl FnMut((), T) -> ControlFlow<(), T> {
             move |(), x| {
-                if predicate(&x) { ControlFlow::Break(x) } else { ControlFlow::Continue(()) }
+                if predicate(&x) { ControlFlow::Break(x) } else { ControlFlow::CONTINUE }
             }
         }
 

core/src/ops/control_flow.rs

@@ -65,3 +65,10 @@ impl<R: Try> ControlFlow<R::Ok, R> {
         }
     }
 }
+
+impl<B> ControlFlow<(), B> {
+    /// It's frequently the case that there's no value needed with `Continue`,
+    /// so this provides a way to avoid typing `(())`, if you prefer it.
+    #[unstable(feature = "control_flow_enum", reason = "new API", issue = "75744")]
+    pub const CONTINUE: Self = ControlFlow::Continue(());
+}