Implement `UpdateFace` for `Polygon`

crates/fj-kernel/src/operations/update/face.rs

@@ -1,5 +1,8 @@
+use std::array;
+
 use crate::{
     objects::{Cycle, Face},
+    operations::Polygon,
     storage::Handle,
 };
 
@@ -47,3 +50,41 @@ impl UpdateFace for Face {
         )
     }
 }
+
+impl<const D: usize> UpdateFace for Polygon<D> {
+    fn update_exterior(
+        &self,
+        f: impl FnOnce(&Handle<Cycle>) -> Handle<Cycle>,
+    ) -> Self {
+        let face = self.face.update_exterior(f);
+        let edges = array::from_fn(|i| {
+            face.exterior()
+                .nth_half_edge(i)
+                .expect("Operation should not have changed length of cycle")
+                .clone()
+        });
+        let vertices = array::from_fn(|i| {
+            // The duplicated code here is unfortunate, but unless we get a
+            // stable `array::each_ref` and something like `array::unzip`, I'm
+            // not sure how to avoid it.
+            face.exterior()
+                .nth_half_edge(i)
+                .expect("Operation should not have changed length of cycle")
+                .start_vertex()
+                .clone()
+        });
+
+        Polygon {
+            face,
+            edges,
+            vertices,
+        }
+    }
+
+    fn add_interiors(
+        &self,
+        _: impl IntoIterator<Item = Handle<Cycle>>,
+    ) -> Self {
+        panic!("Adding interiors to `Polygon` is not supported.")
+    }
+}