core: Implement IntoIterator for Option and Result references

Fixes #27996.

src/libcore/option.rs

@@ -779,6 +779,26 @@ impl<T> IntoIterator for Option<T> {
     }
 }
 
+#[stable(since = "1.4.0", feature = "option_iter")]
+impl<'a, T> IntoIterator for &'a Option<T> {
+    type Item = &'a T;
+    type IntoIter = Iter<'a, T>;
+
+    fn into_iter(self) -> Iter<'a, T> {
+        self.iter()
+    }
+}
+
+#[stable(since = "1.4.0", feature = "option_iter")]
+impl<'a, T> IntoIterator for &'a mut Option<T> {
+    type Item = &'a mut T;
+    type IntoIter = IterMut<'a, T>;
+
+    fn into_iter(mut self) -> IterMut<'a, T> {
+        self.iter_mut()
+    }
+}
+
 /////////////////////////////////////////////////////////////////////////////
 // The Option Iterators
 /////////////////////////////////////////////////////////////////////////////

src/libcore/result.rs

@@ -815,6 +815,26 @@ impl<T, E> IntoIterator for Result<T, E> {
     }
 }
 
+#[stable(since = "1.4.0", feature = "result_iter")]
+impl<'a, T, E> IntoIterator for &'a Result<T, E> {
+    type Item = &'a T;
+    type IntoIter = Iter<'a, T>;
+
+    fn into_iter(self) -> Iter<'a, T> {
+        self.iter()
+    }
+}
+
+#[stable(since = "1.4.0", feature = "result_iter")]
+impl<'a, T, E> IntoIterator for &'a mut Result<T, E> {
+    type Item = &'a mut T;
+    type IntoIter = IterMut<'a, T>;
+
+    fn into_iter(mut self) -> IterMut<'a, T> {
+        self.iter_mut()
+    }
+}
+
 /////////////////////////////////////////////////////////////////////////////
 // The Result Iterators
 /////////////////////////////////////////////////////////////////////////////

src/libcoretest/option.rs

@@ -180,11 +180,14 @@ fn test_iter() {
     assert_eq!(it.next(), Some(&val));
     assert_eq!(it.size_hint(), (0, Some(0)));
     assert!(it.next().is_none());
+
+    let mut it = (&x).into_iter();
+    assert_eq!(it.next(), Some(&val));
 }
 
 #[test]
 fn test_mut_iter() {
-    let val = 5;
+    let mut val = 5;
     let new_val = 11;
 
     let mut x = Some(val);
@@ -205,6 +208,10 @@ fn test_mut_iter() {
         assert!(it.next().is_none());
     }
     assert_eq!(x, Some(new_val));
+
+    let mut y = Some(val);
+    let mut it = (&mut y).into_iter();
+    assert_eq!(it.next(), Some(&mut val));
 }
 
 #[test]

src/libcoretest/result.rs

@@ -150,3 +150,36 @@ pub fn test_expect_err() {
     let err: Result<isize, &'static str> = Err("All good");
     err.expect("Got expected error");
 }
+
+#[test]
+pub fn test_iter() {
+    let ok: Result<isize, &'static str> = Ok(100);
+    let mut it = ok.iter();
+    assert_eq!(it.size_hint(), (1, Some(1)));
+    assert_eq!(it.next(), Some(&100));
+    assert_eq!(it.size_hint(), (0, Some(0)));
+    assert!(it.next().is_none());
+    assert_eq!((&ok).into_iter().next(), Some(&100));
+
+    let err: Result<isize, &'static str> = Err("error");
+    assert_eq!(err.iter().next(), None);
+}
+
+#[test]
+pub fn test_iter_mut() {
+    let mut ok: Result<isize, &'static str> = Ok(100);
+    for loc in ok.iter_mut() {
+        *loc = 200;
+    }
+    assert_eq!(ok, Ok(200));
+    for loc in &mut ok {
+        *loc = 300;
+    }
+    assert_eq!(ok, Ok(300));
+
+    let mut err: Result<isize, &'static str> = Err("error");
+    for loc in err.iter_mut() {
+        *loc = 200;
+    }
+    assert_eq!(err, Err("error"));
+}