Vendor dependencies for 0.3.0 release

vendor/itertools/src/concat_impl.rs

@@ -0,0 +1,27 @@
+/// Combine all an iterator's elements into one element by using [`Extend`].
+///
+/// [`IntoIterator`]-enabled version of [`Itertools::concat`](crate::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,
+{
+    iterable
+        .into_iter()
+        .reduce(|mut a, b| {
+            a.extend(b);
+            a
+        })
+        .unwrap_or_default()
+}