Add Iterator::find_map

Author: matklad

src/libcore/iter/iterator.rs

@@ -1745,6 +1745,38 @@ pub trait Iterator {
         }).break_value()
     }
 
+    /// Applies function to the elements of iterator and returns
+    /// the first non-none result.
+    ///
+    /// `iter.find_map(f)` is equivalent to `iter.filter_map(f).next()`.
+    ///
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(iterator_find_map)]
+    /// let a = ["lol", "NaN", "2", "5"];
+    ///
+    /// let mut first_number = a.iter().find_map(|s| s.parse().ok());
+    ///
+    /// assert_eq!(first_number, Some(2));
+    /// ```
+    #[inline]
+    #[unstable(feature = "iterator_find_map",
+               reason = "unstable new API",
+               issue = "49602")]
+    fn find_map<B, F>(&mut self, mut f: F) -> Option<B> where
+        Self: Sized,
+        F: FnMut(Self::Item) -> Option<B>,
+    {
+        self.try_for_each(move |x| {
+            match f(x) {
+                Some(x) => LoopState::Break(x),
+                None => LoopState::Continue(()),
+            }
+        }).break_value()
+    }
+
     /// Searches for an element in an iterator, returning its index.
     ///
     /// `position()` takes a closure that returns `true` or `false`. It applies

src/libcore/tests/iter.rs

@@ -1146,6 +1146,33 @@ fn test_find() {
     assert!(v.iter().find(|&&x| x % 12 == 0).is_none());
 }
 
+#[test]
+fn test_find_map() {
+    let xs: &[isize] = &[];
+    assert_eq!(xs.iter().find_map(half_if_even), None);
+    let xs: &[isize] = &[3, 5];
+    assert_eq!(xs.iter().find_map(half_if_even), None);
+    let xs: &[isize] = &[4, 5];
+    assert_eq!(xs.iter().find_map(half_if_even), Some(2));
+    let xs: &[isize] = &[3, 6];
+    assert_eq!(xs.iter().find_map(half_if_even), Some(3));
+
+    let xs: &[isize] = &[1, 2, 3, 4, 5, 6, 7];
+    let mut iter = xs.iter();
+    assert_eq!(iter.find_map(half_if_even), Some(1));
+    assert_eq!(iter.find_map(half_if_even), Some(2));
+    assert_eq!(iter.find_map(half_if_even), Some(3));
+    assert_eq!(iter.next(), Some(&7));
+
+    fn half_if_even(x: &isize) -> Option<isize> {
+        if x % 2 == 0 {
+            Some(x / 2)
+        } else {
+            None
+        }
+    }
+}
+
 #[test]
 fn test_position() {
     let v = &[1, 3, 9, 27, 103, 14, 11];

src/libcore/tests/lib.rs

@@ -49,6 +49,7 @@
 #![feature(atomic_nand)]
 #![feature(reverse_bits)]
 #![feature(inclusive_range_fields)]
+#![feature(iterator_find_map)]
 
 extern crate core;
 extern crate test;