CLI tool for updating Route53 DNS for an ASG.

1 files changed, 24 insertions, 0 deletions

diff --git a/src/single.rs b/src/single.rs
new file mode 100644
index 0000000..b3f0b18
--- /dev/null
+++ b/src/single.rs
@@ -0,0 +1,24 @@
+pub trait Single {
+    type Item;
+
+    fn single(self) -> Option<Self::Item>;
+}
+
+impl<T, I> Single for I
+where
+    I: IntoIterator<Item = T>,
+{
+    type Item = T;
+
+    fn single(self) -> Option<Self::Item> {
+        let mut iter = self.into_iter();
+
+        // There are three cases of interest:
+        //
+        // 1. `self` has zero items -> return None.
+        // 2. `self` has two or more items -> return None.
+        // 3. `self` has exactly one item -> return `iter.next()` unchanged, as
+        //    it holds that item.
+        iter.next().filter(|_| iter.next().is_none())
+    }
+}