1 files changed, 150 insertions, 0 deletions
diff --git a/src/filter_x.rs b/src/filter_x.rs
new file mode 100644
index 0000000..8634686
--- /dev/null
+++ b/src/filter_x.rs
@@ -0,0 +1,150 @@
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+//
+
+/// Extension trait for `Iterator<Item = Result<O, E>>` to filter one kind of result (and leaving the other as is)
+pub trait FilterX<O, E> : Sized
+{
+    fn filter_ok<F>(self, F) -> FilterOk<Self, F>
+        where F: FnMut(&O) -> bool;
+    fn filter_err<F>(self, F) -> FilterErr<Self, F>
+        where F: FnMut(&E) -> bool;
+}
+
+impl<I, O, E> FilterX<O, E> for I
+    where I: Iterator<Item = Result<O, E>> + Sized,
+{
+    fn filter_ok<F>(self, f: F) -> FilterOk<Self, F>
+        where F: FnMut(&O) -> bool
+    {
+        FilterOk{ iter: self, f }
+    }
+    fn filter_err<F>(self, f: F) -> FilterErr<Self, F>
+        where F: FnMut(&E) -> bool
+    {
+        FilterErr{ iter: self, f }
+    }
+}
+
+
+#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
+pub struct FilterOk<I, F> {
+    iter: I,
+    f: F,
+}
+
+impl<I, O, E, F> Iterator for FilterOk<I, F>
+    where I: Iterator<Item = Result<O, E>>,
+          F: FnMut(&O) -> bool,
+{
+    type Item = Result<O, E>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        loop {
+            match self.iter.next() {
+                Some(Ok(x)) => {
+                    if (self.f)(&x) {
+                        return Some(Ok(x));
+                    }
+                }
+                other => { return other; }
+            }
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let hint_sup = self.iter.size_hint().1;
+        (0, hint_sup)
+    }
+}
+
+
+#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
+pub struct FilterErr<I, F> {
+    iter: I,
+    f: F,
+}
+
+impl<I, O, E, F> Iterator for FilterErr<I, F>
+    where I: Iterator<Item = Result<O, E>>,
+          F: FnMut(&E) -> bool,
+{
+    type Item = Result<O, E>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        loop {
+            match self.iter.next() {
+                Some(Err(x)) => {
+                    if (self.f)(&x) {
+                        return Some(Err(x));
+                    }
+                }
+                other => { return other; }
+            }
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let hint_sup = self.iter.size_hint().1;
+        (0, hint_sup)
+    }
+}
+
+
+#[test]
+fn test_filter_ok() {
+    use std::str::FromStr;
+
+    let mapped: Vec<_> = ["1", "2", "a", "4", "5"]
+        .into_iter()
+        .map(|txt| usize::from_str(txt))
+        .filter_ok(|i| i%2 == 0)
+        .collect();
+
+    assert_eq!(mapped.len(), 3);
+    assert_eq!(mapped[0], Ok(2));
+    assert_eq!(mapped[2], Ok(4));
+}
+
+#[test]
+fn test_filter_ok_hint() {
+    use std::str::FromStr;
+
+    let hint = ["1", "2", "a", "4", "5"]
+        .into_iter()
+        .map(|txt| usize::from_str(txt))
+        .filter_ok(|i| i%2 == 0)
+        .size_hint();
+
+    assert_eq!(hint, (0, Some(5)));
+}
+
+#[test]
+fn test_filter_err() {
+    use std::str::FromStr;
+
+    let mapped: Vec<_> = ["1", "2", "a", "4", "5"]
+        .into_iter()
+        .map(|txt| usize::from_str(txt))
+        .filter_err(|_| false)
+        .collect();
+
+    assert_eq!(mapped, vec![Ok(1), Ok(2), Ok(4), Ok(5)]);
+}
+
+#[test]
+fn test_filter_err_hint() {
+    use std::str::FromStr;
+
+    let hint = ["1", "2", "a", "4", "5"]
+        .into_iter()
+        .map(|txt| usize::from_str(txt))
+        .filter_err(|_| false)
+        .size_hint();
+
+    assert_eq!(hint, (0, Some(5)));
+}