Add Itertools::enumerate_ok

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Co-authored-by: Saatvik Shah <6854735+saatvikshah@users.noreply.github.com>
Co-authored-by: Roland Fredenhagen <dev@modprog.de>
Co-authored-by: Shahar Dawn Or <mightyiampresence@gmail.com>
Co-authored-by: Preet Dua <615318+prabhpreet@users.noreply.github.com>

src/adaptors/mod.rs

@@ -839,6 +839,50 @@ impl_tuple_combination!(Tuple10Combination Tuple9Combination; a b c d e f g h i)
 impl_tuple_combination!(Tuple11Combination Tuple10Combination; a b c d e f g h i j);
 impl_tuple_combination!(Tuple12Combination Tuple11Combination; a b c d e f g h i j k);
 
+/// An iterator adapter to enumerate values within a nested `Result::Ok`.
+///
+/// See [`.enumerate_ok()`](crate::Itertools::enumerate_ok) for more information.
+#[derive(Clone)]
+#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
+pub struct EnumerateOk<I> {
+    iter: I,
+    index: usize
+}
+
+/// Create a new `EnumerateOk` iterator.
+pub fn enumerate_ok<I, T, E>(iter: I) -> EnumerateOk<I>
+where
+    I: Iterator<Item = Result<T, E>>,
+{
+    EnumerateOk {
+        iter,
+        index: 0
+    }
+}
+
+impl<I> fmt::Debug for EnumerateOk<I>
+where
+    I: fmt::Debug,
+{
+    debug_fmt_fields!(EnumerateOk, iter);
+}
+
+impl<I,T,E> Iterator for EnumerateOk<I>
+    where I: Iterator<Item = Result<T,E>>,
+{
+    type Item = Result<(usize,T),E>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.iter.next().map(|item| {
+            item.map(|v| {
+                let index = self.index;
+                self.index +=1;
+                (index,v)
+            })
+        })
+    }
+}
+
 /// An iterator adapter to filter values within a nested `Result::Ok`.
 ///
 /// See [`.filter_ok()`](crate::Itertools::filter_ok) for more information.

src/lib.rs

@@ -99,6 +99,7 @@ pub mod structs {
         Batching,
         MapInto,
         MapOk,
+        EnumerateOk,
         Merge,
         MergeBy,
         TakeWhileRef,
@@ -846,6 +847,23 @@ pub trait Itertools : Iterator {
         self.map_ok(f)
     }
 
+    /// Return an iterator adaptor that adds an index to `Result::Ok`
+    /// values. `Result::Err` values are unchanged. The index is incremented
+    /// only for `Result::Ok` values.
+    ///
+    /// ```
+    /// use itertools::Itertools;
+    ///
+    /// let input = vec![Ok(41), Err(false), Ok(11)];
+    /// let it = input.into_iter().enumerate_ok();
+    /// itertools::assert_equal(it, vec![Ok((0, 41)), Err(false), Ok((1, 11))]);
+    /// ```
+    fn enumerate_ok<T, E>(self) -> EnumerateOk<Self>
+        where Self: Iterator<Item = Result<T, E>> + Sized,
+    {
+        adaptors::enumerate_ok(self)
+    }
+
     /// Return an iterator adaptor that applies the provided closure
     /// to every `Result::Ok` value. `Result::Err` values are
     /// unchanged.