Pre: implement IntoIterator for ValueTypeSet.

query-algebrizer/src/types.rs

@@ -582,3 +582,28 @@ impl ValueTypeSet {
         self.0.len() == 1
     }
 }
+
+impl IntoIterator for ValueTypeSet {
+    type Item = ValueType;
+    type IntoIter = ::enum_set::Iter<ValueType>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.0.into_iter()
+    }
+}
+
+impl ::std::iter::FromIterator<ValueType> for ValueTypeSet {
+    fn from_iter<I: IntoIterator<Item = ValueType>>(iterator: I) -> Self {
+        let mut ret = Self::none();
+        ret.0.extend(iterator);
+        ret
+    }
+}
+
+impl ::std::iter::Extend<ValueType> for ValueTypeSet {
+    fn extend<I: IntoIterator<Item = ValueType>>(&mut self, iter: I) {
+        for element in iter {
+            self.0.insert(element);
+        }
+    }
+}