Implement Columnation for PointStamp (#410)

This change implements support for `Columnation` for `PointStamp`.

src/dynamic/pointstamp.rs

@@ -202,3 +202,51 @@ impl<T: Lattice + Timestamp + Clone> Lattice for PointStamp<T> {
         Self { vector }
     }
 }
+
+use timely::container::columnation::{Columnation, Region};
+impl<T: Columnation> Columnation for PointStamp<T> {
+    type InnerRegion = PointStampStack<T::InnerRegion>;
+}
+
+/// Stack for PointStamp. Part of Columnation implementation.
+pub struct PointStampStack<R: Region>(<Vec<R::Item> as Columnation>::InnerRegion)
+where
+    <R as Region>::Item: Columnation;
+
+impl<R: Region> Default for PointStampStack<R>
+    where
+        <R as Region>::Item: Columnation
+{
+    #[inline]
+    fn default() -> Self {
+        Self(Default::default())
+    }
+}
+
+impl<R: Region> Region for PointStampStack<R>
+    where
+        <R as Region>::Item: Columnation
+{
+    type Item = PointStamp<R::Item>;
+
+    #[inline]
+    unsafe fn copy(&mut self, item: &Self::Item) -> Self::Item {
+        Self::Item { vector: self.0.copy(&item.vector) }
+    }
+
+    fn clear(&mut self) {
+        self.0.clear();
+    }
+
+    fn reserve_items<'a, I>(&mut self, items: I) where Self: 'a, I: Iterator<Item=&'a Self::Item> + Clone {
+        self.0.reserve_items(items.map(|x| &x.vector));
+    }
+
+    fn reserve_regions<'a, I>(&mut self, regions: I) where Self: 'a, I: Iterator<Item=&'a Self> + Clone {
+        self.0.reserve_regions(regions.map(|r| &r.0));
+    }
+
+    fn heap_size(&self, callback: impl FnMut(usize, usize)) {
+        self.0.heap_size(callback);
+    }
+}