1 files changed, 23 insertions, 0 deletions
diff --git a/third_party/rust/itertools/src/concat_impl.rs b/third_party/rust/itertools/src/concat_impl.rs
new file mode 100644
index 0000000000..f022ec90af
--- /dev/null
+++ b/third_party/rust/itertools/src/concat_impl.rs
@@ -0,0 +1,23 @@
+use crate::Itertools;
+
+/// Combine all an iterator's elements into one element by using [`Extend`].
+///
+/// [`IntoIterator`]-enabled version of [`Itertools::concat`].
+///
+/// This combinator will extend the first item with each of the rest of the
+/// items of the iterator. If the iterator is empty, the default value of
+/// `I::Item` is returned.
+///
+/// ```rust
+/// use itertools::concat;
+/// 
+/// let input = vec![vec![1], vec![2, 3], vec![4, 5, 6]];
+/// assert_eq!(concat(input), vec![1, 2, 3, 4, 5, 6]);
+/// ```
+pub fn concat<I>(iterable: I) -> I::Item
+    where I: IntoIterator,
+          I::Item: Extend<<<I as IntoIterator>::Item as IntoIterator>::Item> + IntoIterator + Default
+{
+    #[allow(deprecated)] //TODO: once msrv hits 1.51. replace `fold1` with `reduce`
+    iterable.into_iter().fold1(|mut a, b| { a.extend(b); a }).unwrap_or_default()
+}