1 files changed, 33 insertions, 0 deletions
diff --git a/library/alloc/src/collections/vec_deque/spec_from_iter.rs b/library/alloc/src/collections/vec_deque/spec_from_iter.rs
new file mode 100644
index 000000000..7650492eb
--- /dev/null
+++ b/library/alloc/src/collections/vec_deque/spec_from_iter.rs
@@ -0,0 +1,33 @@
+use super::{IntoIter, VecDeque};
+
+/// Specialization trait used for `VecDeque::from_iter`
+pub(super) trait SpecFromIter<T, I> {
+    fn spec_from_iter(iter: I) -> Self;
+}
+
+impl<T, I> SpecFromIter<T, I> for VecDeque<T>
+where
+    I: Iterator<Item = T>,
+{
+    default fn spec_from_iter(iterator: I) -> Self {
+        // Since converting is O(1) now, just re-use the `Vec` logic for
+        // anything where we can't do something extra-special for `VecDeque`,
+        // especially as that could save us some monomorphiziation work
+        // if one uses the same iterators (like slice ones) with both.
+        crate::vec::Vec::from_iter(iterator).into()
+    }
+}
+
+impl<T> SpecFromIter<T, crate::vec::IntoIter<T>> for VecDeque<T> {
+    #[inline]
+    fn spec_from_iter(iterator: crate::vec::IntoIter<T>) -> Self {
+        iterator.into_vecdeque()
+    }
+}
+
+impl<T> SpecFromIter<T, IntoIter<T>> for VecDeque<T> {
+    #[inline]
+    fn spec_from_iter(iterator: IntoIter<T>) -> Self {
+        iterator.into_vecdeque()
+    }
+}