Add BREAK too, and improve the comments

Author: scottmcm

core/src/iter/traits/iterator.rs

@@ -2086,10 +2086,10 @@ pub trait Iterator {
         #[inline]
         fn check<T>(mut f: impl FnMut(T) -> bool) -> impl FnMut((), T) -> ControlFlow<(), ()> {
             move |(), x| {
-                if f(x) { ControlFlow::Continue(()) } else { ControlFlow::Break(()) }
+                if f(x) { ControlFlow::CONTINUE } else { ControlFlow::BREAK }
             }
         }
-        self.try_fold((), check(f)) == ControlFlow::Continue(())
+        self.try_fold((), check(f)) == ControlFlow::CONTINUE
     }
 
     /// Tests if any element of the iterator matches a predicate.
@@ -2139,11 +2139,11 @@ pub trait Iterator {
         #[inline]
         fn check<T>(mut f: impl FnMut(T) -> bool) -> impl FnMut((), T) -> ControlFlow<(), ()> {
             move |(), x| {
-                if f(x) { ControlFlow::Break(()) } else { ControlFlow::Continue(()) }
+                if f(x) { ControlFlow::BREAK } else { ControlFlow::CONTINUE }
             }
         }
 
-        self.try_fold((), check(f)) == ControlFlow::Break(())
+        self.try_fold((), check(f)) == ControlFlow::BREAK
     }
 
     /// Searches for an element of an iterator that satisfies a predicate.
@@ -2201,7 +2201,7 @@ pub trait 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 }
             }
         }
 
@@ -2236,7 +2236,7 @@ pub trait Iterator {
         ) -> impl FnMut((), T) -> ControlFlow<(), B> {
             move |(), x| match f(x) {
                 Some(x) => ControlFlow::Break(x),
-                None => ControlFlow::Continue(()),
+                None => ControlFlow::CONTINUE,
             }
         }
 
@@ -2278,7 +2278,7 @@ pub trait Iterator {
             R: Try<Ok = bool>,
         {
             move |(), x| match f(&x).into_result() {
-                Ok(false) => ControlFlow::Continue(()),
+                Ok(false) => ControlFlow::CONTINUE,
                 Ok(true) => ControlFlow::Break(Ok(x)),
                 Err(x) => ControlFlow::Break(Err(x)),
             }

core/src/ops/control_flow.rs

@@ -69,6 +69,42 @@ 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.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(control_flow_enum)]
+    /// use std::ops::ControlFlow;
+    ///
+    /// let mut partial_sum = 0;
+    /// let last_used = (1..10).chain(20..25).try_for_each(|x| {
+    ///     partial_sum += x;
+    ///     if partial_sum > 100 { ControlFlow::Break(x) }
+    ///     else { ControlFlow::CONTINUE }
+    /// });
+    /// assert_eq!(last_used.break_value(), Some(22));
+    /// ```
     #[unstable(feature = "control_flow_enum", reason = "new API", issue = "75744")]
     pub const CONTINUE: Self = ControlFlow::Continue(());
 }
+
+impl<C> ControlFlow<C, ()> {
+    /// APIs like `try_for_each` don't need values with `Break`,
+    /// so this provides a way to avoid typing `(())`, if you prefer it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(control_flow_enum)]
+    /// use std::ops::ControlFlow;
+    ///
+    /// let mut partial_sum = 0;
+    /// (1..10).chain(20..25).try_for_each(|x| {
+    ///     if partial_sum > 100 { ControlFlow::BREAK }
+    ///     else { partial_sum += x; ControlFlow::CONTINUE }
+    /// });
+    /// assert_eq!(partial_sum, 108);
+    /// ```
+    #[unstable(feature = "control_flow_enum", reason = "new API", issue = "75744")]
+    pub const BREAK: Self = ControlFlow::Break(());
+}