From 83ae3846e344a3d56e4058740d482a50d968d28a Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Tue, 8 Mar 2022 13:10:16 +0100
Subject: [PATCH 01/21] Move `Faces` to `shape::faces`

---
 src/kernel/algorithms/sweep.rs     |  4 ++--
 src/kernel/shape/faces.rs          | 22 ++++++++++++++++++++++
 src/kernel/shape/mod.rs            |  8 ++++++--
 src/kernel/shapes/circle.rs        |  4 ++--
 src/kernel/shapes/difference_2d.rs |  7 ++-----
 src/kernel/shapes/sketch.rs        |  4 ++--
 src/kernel/shapes/union.rs         |  2 +-
 src/kernel/topology/faces.rs       | 17 -----------------
 8 files changed, 37 insertions(+), 31 deletions(-)
 create mode 100644 src/kernel/shape/faces.rs

diff --git a/src/kernel/algorithms/sweep.rs b/src/kernel/algorithms/sweep.rs
index b0c155758..46dbfcb0f 100644
--- a/src/kernel/algorithms/sweep.rs
+++ b/src/kernel/algorithms/sweep.rs
@@ -1,7 +1,7 @@
 use crate::{
     kernel::{
-        shape::Shape,
-        topology::faces::{Face, Faces},
+        shape::{faces::Faces, Shape},
+        topology::faces::Face,
     },
     math::{Scalar, Transform, Vector},
 };
diff --git a/src/kernel/shape/faces.rs b/src/kernel/shape/faces.rs
new file mode 100644
index 000000000..5a07deede
--- /dev/null
+++ b/src/kernel/shape/faces.rs
@@ -0,0 +1,22 @@
+use crate::{
+    debug::DebugInfo,
+    kernel::topology::faces::Face,
+    math::{Scalar, Triangle},
+};
+
+/// The faces of a shape
+#[derive(Clone, Debug, Eq, PartialEq, Hash, Ord, PartialOrd)]
+pub struct Faces(pub Vec<Face>);
+
+impl Faces {
+    pub fn triangles(
+        &self,
+        tolerance: Scalar,
+        out: &mut Vec<Triangle<3>>,
+        debug_info: &mut DebugInfo,
+    ) {
+        for face in &self.0 {
+            face.triangles(tolerance, out, debug_info);
+        }
+    }
+}
diff --git a/src/kernel/shape/mod.rs b/src/kernel/shape/mod.rs
index dc8719697..becb1928d 100644
--- a/src/kernel/shape/mod.rs
+++ b/src/kernel/shape/mod.rs
@@ -1,13 +1,17 @@
 pub mod cycles;
 pub mod edges;
+pub mod faces;
 pub mod handle;
 pub mod vertices;
 
 use crate::math::Scalar;
 
-use super::topology::{edges::Cycle, faces::Faces, vertices::Vertex};
+use super::topology::{edges::Cycle, vertices::Vertex};
 
-use self::{cycles::Cycles, edges::Edges, handle::Storage, vertices::Vertices};
+use self::{
+    cycles::Cycles, edges::Edges, faces::Faces, handle::Storage,
+    vertices::Vertices,
+};
 
 /// The boundary representation of a shape
 ///
diff --git a/src/kernel/shapes/circle.rs b/src/kernel/shapes/circle.rs
index f6304730f..a304a3d59 100644
--- a/src/kernel/shapes/circle.rs
+++ b/src/kernel/shapes/circle.rs
@@ -2,10 +2,10 @@ use crate::{
     debug::DebugInfo,
     kernel::{
         geometry::Surface,
-        shape::Shape,
+        shape::{faces::Faces, Shape},
         topology::{
             edges::{Cycle, Edge},
-            faces::{Face, Faces},
+            faces::Face,
         },
     },
     math::{Aabb, Point, Scalar},
diff --git a/src/kernel/shapes/difference_2d.rs b/src/kernel/shapes/difference_2d.rs
index 31394126e..a6874e85c 100644
--- a/src/kernel/shapes/difference_2d.rs
+++ b/src/kernel/shapes/difference_2d.rs
@@ -1,11 +1,8 @@
 use crate::{
     debug::DebugInfo,
     kernel::{
-        shape::Shape,
-        topology::{
-            edges::Cycle,
-            faces::{Face, Faces},
-        },
+        shape::{faces::Faces, Shape},
+        topology::{edges::Cycle, faces::Face},
     },
     math::{Aabb, Scalar},
 };
diff --git a/src/kernel/shapes/sketch.rs b/src/kernel/shapes/sketch.rs
index 601a131de..26cd33789 100644
--- a/src/kernel/shapes/sketch.rs
+++ b/src/kernel/shapes/sketch.rs
@@ -2,10 +2,10 @@ use crate::{
     debug::DebugInfo,
     kernel::{
         geometry::Surface,
-        shape::Shape,
+        shape::{faces::Faces, Shape},
         topology::{
             edges::{Cycle, Edge},
-            faces::{Face, Faces},
+            faces::Face,
         },
     },
     math::{Aabb, Point, Scalar},
diff --git a/src/kernel/shapes/union.rs b/src/kernel/shapes/union.rs
index 9c35d85b5..f47a8b82e 100644
--- a/src/kernel/shapes/union.rs
+++ b/src/kernel/shapes/union.rs
@@ -1,6 +1,6 @@
 use crate::{
     debug::DebugInfo,
-    kernel::{shape::Shape, topology::faces::Faces},
+    kernel::shape::{faces::Faces, Shape},
     math::{Aabb, Scalar},
 };
 
diff --git a/src/kernel/topology/faces.rs b/src/kernel/topology/faces.rs
index c11461391..3f51e1ac9 100644
--- a/src/kernel/topology/faces.rs
+++ b/src/kernel/topology/faces.rs
@@ -16,23 +16,6 @@ use crate::{
 
 use super::edges::Cycle;
 
-/// The faces of a shape
-#[derive(Clone, Debug, Eq, PartialEq, Hash, Ord, PartialOrd)]
-pub struct Faces(pub Vec<Face>);
-
-impl Faces {
-    pub fn triangles(
-        &self,
-        tolerance: Scalar,
-        out: &mut Vec<Triangle<3>>,
-        debug_info: &mut DebugInfo,
-    ) {
-        for face in &self.0 {
-            face.triangles(tolerance, out, debug_info);
-        }
-    }
-}
-
 /// A face of a shape
 #[derive(Clone, Debug, Eq, PartialEq, Hash, Ord, PartialOrd)]
 pub enum Face {

From 4c276addd5b7b5d769d2a150b1082c788c9516e1 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Tue, 8 Mar 2022 13:14:11 +0100
Subject: [PATCH 02/21] Take `Shape` by value in `transform_shape`

I'm certain this is not what this function signature will look like
long-term, but for now, it will help with the next steps. And it doesn't
cause problems for the single caller.
---
 src/kernel/algorithms/transform.rs | 2 +-
 src/kernel/shapes/transform.rs     | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/kernel/algorithms/transform.rs b/src/kernel/algorithms/transform.rs
index 2dc1cc7d6..5031f2b40 100644
--- a/src/kernel/algorithms/transform.rs
+++ b/src/kernel/algorithms/transform.rs
@@ -19,7 +19,7 @@ use crate::{
 ///
 /// Addressing the shortcomings in this method probably doesn't make sense,
 /// except as a side effect of addressing the shortcomings of `Shape`.
-pub fn transform_shape(original: &Shape, transform: &Transform) -> Shape {
+pub fn transform_shape(original: Shape, transform: &Transform) -> Shape {
     let mut transformed = Shape::new();
 
     for face in &original.faces.0 {
diff --git a/src/kernel/shapes/transform.rs b/src/kernel/shapes/transform.rs
index 79f22d30e..3c3513f49 100644
--- a/src/kernel/shapes/transform.rs
+++ b/src/kernel/shapes/transform.rs
@@ -12,7 +12,7 @@ impl ToShape for fj::Transform {
     fn to_shape(&self, tolerance: Scalar, debug_info: &mut DebugInfo) -> Shape {
         let shape = self.shape.to_shape(tolerance, debug_info);
         let transform = transform(self);
-        transform_shape(&shape, &transform)
+        transform_shape(shape, &transform)
     }
 
     fn bounding_volume(&self) -> Aabb<3> {

From 43f7778927ae37ba29bf733b3a6281afc2c62778 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Tue, 8 Mar 2022 13:16:00 +0100
Subject: [PATCH 03/21] Refactor

---
 src/kernel/shapes/union.rs | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/kernel/shapes/union.rs b/src/kernel/shapes/union.rs
index f47a8b82e..8f3ecf7e4 100644
--- a/src/kernel/shapes/union.rs
+++ b/src/kernel/shapes/union.rs
@@ -10,8 +10,8 @@ impl ToShape for fj::Union {
     fn to_shape(&self, tolerance: Scalar, debug_info: &mut DebugInfo) -> Shape {
         let mut shape = Shape::new();
 
-        let a = self.a.to_shape(tolerance, debug_info).faces;
-        let b = self.b.to_shape(tolerance, debug_info).faces;
+        let a = self.a.to_shape(tolerance, debug_info).faces.0;
+        let b = self.b.to_shape(tolerance, debug_info).faces.0;
 
         // This doesn't create a true union, as it doesn't eliminate, merge, or
         // split faces.
@@ -19,8 +19,8 @@ impl ToShape for fj::Union {
         // See issue:
         // https://github.com/hannobraun/Fornjot/issues/42
         let mut faces = Vec::new();
-        faces.extend(a.0);
-        faces.extend(b.0);
+        faces.extend(a);
+        faces.extend(b);
 
         shape.faces = Faces(faces);
 

From 353dfc80b1b15572286cd1e422b6cefe7f730ec4 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Tue, 8 Mar 2022 13:17:53 +0100
Subject: [PATCH 04/21] Refactor

---
 src/main.rs | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index 43230e146..89dd0b8af 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -100,10 +100,12 @@ fn main() -> anyhow::Result<()> {
     };
 
     let mut debug_info = DebugInfo::new();
-    let faces = shape.to_shape(tolerance, &mut debug_info).faces;
-
     let mut triangles = Vec::new();
-    faces.triangles(tolerance, &mut triangles, &mut debug_info);
+    shape.to_shape(tolerance, &mut debug_info).faces.triangles(
+        tolerance,
+        &mut triangles,
+        &mut debug_info,
+    );
 
     if let Some(path) = args.export {
         let mut mesh_maker = MeshMaker::new();

From cc39e911219aaffbdf17202d63f3ceb925778748 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Tue, 8 Mar 2022 13:19:14 +0100
Subject: [PATCH 05/21] Refactor

---
 src/main.rs | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index 89dd0b8af..0f37241f0 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -228,10 +228,12 @@ fn main() -> anyhow::Result<()> {
                 debug_info.clear();
                 triangles.clear();
 
-                let faces = shape.to_shape(tolerance, &mut debug_info).faces;
-
                 aabb = shape.bounding_volume();
-                faces.triangles(tolerance, &mut triangles, &mut debug_info);
+                shape.to_shape(tolerance, &mut debug_info).faces.triangles(
+                    tolerance,
+                    &mut triangles,
+                    &mut debug_info,
+                );
 
                 renderer.update_geometry(
                     (&triangles).into(),

From e0bb22d6e5353c05cfb32519d18040ce302c4509 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Tue, 8 Mar 2022 13:20:18 +0100
Subject: [PATCH 06/21] Add `Shape::faces`

---
 src/kernel/algorithms/sweep.rs     | 12 ++++++------
 src/kernel/algorithms/transform.rs |  6 +++---
 src/kernel/shape/mod.rs            |  5 +++++
 src/kernel/shapes/circle.rs        |  2 +-
 src/kernel/shapes/difference_2d.rs |  6 +++---
 src/kernel/shapes/sketch.rs        |  2 +-
 src/kernel/shapes/union.rs         |  6 +++---
 src/main.rs                        | 18 ++++++++----------
 8 files changed, 30 insertions(+), 27 deletions(-)

diff --git a/src/kernel/algorithms/sweep.rs b/src/kernel/algorithms/sweep.rs
index 46dbfcb0f..6474c27c8 100644
--- a/src/kernel/algorithms/sweep.rs
+++ b/src/kernel/algorithms/sweep.rs
@@ -22,7 +22,7 @@ pub fn sweep_shape(
     let mut top_faces = Vec::new();
     let mut side_faces = Vec::new();
 
-    for face in &original.faces.0 {
+    for face in &original.faces().0 {
         bottom_faces.push(face.clone());
         top_faces.push(transform_face(face, &translation, &mut shape));
     }
@@ -60,7 +60,7 @@ pub fn sweep_shape(
     faces.extend(top_faces);
     faces.extend(side_faces);
 
-    shape.faces = Faces(faces);
+    *shape.faces() = Faces(faces);
 
     shape
 }
@@ -85,7 +85,7 @@ mod tests {
     fn sweep() {
         let sketch = Triangle::new([[0., 0., 0.], [1., 0., 0.], [0., 1., 0.]]);
 
-        let swept = sweep_shape(
+        let mut swept = sweep_shape(
             sketch.shape,
             Vector::from([0., 0., 1.]),
             Scalar::from_f64(0.),
@@ -95,8 +95,8 @@ mod tests {
         let top_face =
             Triangle::new([[0., 0., 1.], [1., 0., 1.], [0., 1., 1.]]).face;
 
-        assert!(swept.faces.0.contains(&bottom_face));
-        assert!(swept.faces.0.contains(&top_face));
+        assert!(swept.faces().0.contains(&bottom_face));
+        assert!(swept.faces().0.contains(&top_face));
 
         // Side faces are not tested, as those use triangle representation. The
         // plan is to start testing them, as they are transitioned to b-rep.
@@ -134,7 +134,7 @@ mod tests {
                 }],
             };
 
-            shape.faces.0.push(abc.clone());
+            shape.faces().0.push(abc.clone());
 
             Self { shape, face: abc }
         }
diff --git a/src/kernel/algorithms/transform.rs b/src/kernel/algorithms/transform.rs
index 5031f2b40..0d937316f 100644
--- a/src/kernel/algorithms/transform.rs
+++ b/src/kernel/algorithms/transform.rs
@@ -19,12 +19,12 @@ use crate::{
 ///
 /// Addressing the shortcomings in this method probably doesn't make sense,
 /// except as a side effect of addressing the shortcomings of `Shape`.
-pub fn transform_shape(original: Shape, transform: &Transform) -> Shape {
+pub fn transform_shape(mut original: Shape, transform: &Transform) -> Shape {
     let mut transformed = Shape::new();
 
-    for face in &original.faces.0 {
+    for face in &original.faces().0 {
         let face = transform_face(face, transform, &mut transformed);
-        transformed.faces.0.push(face);
+        transformed.faces().0.push(face);
     }
 
     transformed
diff --git a/src/kernel/shape/mod.rs b/src/kernel/shape/mod.rs
index becb1928d..a4bb16168 100644
--- a/src/kernel/shape/mod.rs
+++ b/src/kernel/shape/mod.rs
@@ -82,6 +82,11 @@ impl Shape {
             cycles: &mut self.cycles,
         }
     }
+
+    /// Access the shape's faces
+    pub fn faces(&mut self) -> &mut Faces {
+        &mut self.faces
+    }
 }
 
 type VerticesInner = Vec<Storage<Vertex>>;
diff --git a/src/kernel/shapes/circle.rs b/src/kernel/shapes/circle.rs
index a304a3d59..c6e3ce36d 100644
--- a/src/kernel/shapes/circle.rs
+++ b/src/kernel/shapes/circle.rs
@@ -25,7 +25,7 @@ impl ToShape for fj::Circle {
             .add(Edge::circle(Scalar::from_f64(self.radius)));
         shape.cycles().add(Cycle { edges: vec![edge] });
 
-        shape.faces = Faces(vec![Face::Face {
+        *shape.faces() = Faces(vec![Face::Face {
             cycles: shape
                 .cycles()
                 .all()
diff --git a/src/kernel/shapes/difference_2d.rs b/src/kernel/shapes/difference_2d.rs
index a6874e85c..6325c5d86 100644
--- a/src/kernel/shapes/difference_2d.rs
+++ b/src/kernel/shapes/difference_2d.rs
@@ -38,10 +38,10 @@ impl ToShape for fj::Difference2d {
             );
         }
 
-        shape.faces = {
-            let (a, b) = if a.faces.0.len() == 1 && b.faces.0.len() == 1 {
+        *shape.faces() = {
+            let (a, b) = if a.faces().0.len() == 1 && b.faces().0.len() == 1 {
                 // Can't panic. We just checked that length of `a` and `b` is 1.
-                (a.faces.0.pop().unwrap(), b.faces.0.pop().unwrap())
+                (a.faces().0.pop().unwrap(), b.faces().0.pop().unwrap())
             } else {
                 // See issue:
                 // https://github.com/hannobraun/Fornjot/issues/95
diff --git a/src/kernel/shapes/sketch.rs b/src/kernel/shapes/sketch.rs
index 26cd33789..9ca26f789 100644
--- a/src/kernel/shapes/sketch.rs
+++ b/src/kernel/shapes/sketch.rs
@@ -55,7 +55,7 @@ impl ToShape for fj::Sketch {
                 .collect(),
             surface: Surface::x_y_plane(),
         };
-        shape.faces = Faces(vec![face]);
+        *shape.faces() = Faces(vec![face]);
 
         shape
     }
diff --git a/src/kernel/shapes/union.rs b/src/kernel/shapes/union.rs
index 8f3ecf7e4..fc98b0d80 100644
--- a/src/kernel/shapes/union.rs
+++ b/src/kernel/shapes/union.rs
@@ -10,8 +10,8 @@ impl ToShape for fj::Union {
     fn to_shape(&self, tolerance: Scalar, debug_info: &mut DebugInfo) -> Shape {
         let mut shape = Shape::new();
 
-        let a = self.a.to_shape(tolerance, debug_info).faces.0;
-        let b = self.b.to_shape(tolerance, debug_info).faces.0;
+        let a = self.a.to_shape(tolerance, debug_info).faces().0.clone();
+        let b = self.b.to_shape(tolerance, debug_info).faces().0.clone();
 
         // This doesn't create a true union, as it doesn't eliminate, merge, or
         // split faces.
@@ -22,7 +22,7 @@ impl ToShape for fj::Union {
         faces.extend(a);
         faces.extend(b);
 
-        shape.faces = Faces(faces);
+        *shape.faces() = Faces(faces);
 
         shape
     }
diff --git a/src/main.rs b/src/main.rs
index 0f37241f0..43e5e634a 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -101,11 +101,10 @@ fn main() -> anyhow::Result<()> {
 
     let mut debug_info = DebugInfo::new();
     let mut triangles = Vec::new();
-    shape.to_shape(tolerance, &mut debug_info).faces.triangles(
-        tolerance,
-        &mut triangles,
-        &mut debug_info,
-    );
+    shape
+        .to_shape(tolerance, &mut debug_info)
+        .faces()
+        .triangles(tolerance, &mut triangles, &mut debug_info);
 
     if let Some(path) = args.export {
         let mut mesh_maker = MeshMaker::new();
@@ -229,11 +228,10 @@ fn main() -> anyhow::Result<()> {
                 triangles.clear();
 
                 aabb = shape.bounding_volume();
-                shape.to_shape(tolerance, &mut debug_info).faces.triangles(
-                    tolerance,
-                    &mut triangles,
-                    &mut debug_info,
-                );
+                shape
+                    .to_shape(tolerance, &mut debug_info)
+                    .faces()
+                    .triangles(tolerance, &mut triangles, &mut debug_info);
 
                 renderer.update_geometry(
                     (&triangles).into(),

From cf5efbc1a4ff5abd0e88fed73acda73e4500e546 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Tue, 8 Mar 2022 13:20:52 +0100
Subject: [PATCH 07/21] Remove unnecessary `pub`

---
 src/kernel/shape/mod.rs | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/kernel/shape/mod.rs b/src/kernel/shape/mod.rs
index a4bb16168..ad0c9f88f 100644
--- a/src/kernel/shape/mod.rs
+++ b/src/kernel/shape/mod.rs
@@ -29,8 +29,7 @@ pub struct Shape {
 
     vertices: VerticesInner,
     cycles: CyclesInner,
-
-    pub faces: Faces,
+    faces: Faces,
 }
 
 impl Shape {

From e18868611b80d95149ab6f328a381872997f84d3 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Tue, 8 Mar 2022 13:27:42 +0100
Subject: [PATCH 08/21] Refactor

---
 src/kernel/shapes/union.rs | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/kernel/shapes/union.rs b/src/kernel/shapes/union.rs
index fc98b0d80..524e009e1 100644
--- a/src/kernel/shapes/union.rs
+++ b/src/kernel/shapes/union.rs
@@ -10,8 +10,8 @@ impl ToShape for fj::Union {
     fn to_shape(&self, tolerance: Scalar, debug_info: &mut DebugInfo) -> Shape {
         let mut shape = Shape::new();
 
-        let a = self.a.to_shape(tolerance, debug_info).faces().0.clone();
-        let b = self.b.to_shape(tolerance, debug_info).faces().0.clone();
+        let mut a = self.a.to_shape(tolerance, debug_info);
+        let mut b = self.b.to_shape(tolerance, debug_info);
 
         // This doesn't create a true union, as it doesn't eliminate, merge, or
         // split faces.
@@ -19,8 +19,8 @@ impl ToShape for fj::Union {
         // See issue:
         // https://github.com/hannobraun/Fornjot/issues/42
         let mut faces = Vec::new();
-        faces.extend(a);
-        faces.extend(b);
+        faces.extend(a.faces().0.clone());
+        faces.extend(b.faces().0.clone());
 
         *shape.faces() = Faces(faces);
 

From ae3bbb3d67d5a2aff642a25b739690e0b35484d7 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Tue, 8 Mar 2022 13:29:46 +0100
Subject: [PATCH 09/21] Add `Faces::all`

---
 src/kernel/algorithms/sweep.rs     | 4 ++--
 src/kernel/algorithms/transform.rs | 4 ++--
 src/kernel/shape/faces.rs          | 5 +++++
 src/kernel/shapes/difference_2d.rs | 9 +++++++--
 src/kernel/shapes/union.rs         | 4 ++--
 5 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/src/kernel/algorithms/sweep.rs b/src/kernel/algorithms/sweep.rs
index 6474c27c8..0218c09ea 100644
--- a/src/kernel/algorithms/sweep.rs
+++ b/src/kernel/algorithms/sweep.rs
@@ -22,9 +22,9 @@ pub fn sweep_shape(
     let mut top_faces = Vec::new();
     let mut side_faces = Vec::new();
 
-    for face in &original.faces().0 {
+    for face in original.faces().all() {
         bottom_faces.push(face.clone());
-        top_faces.push(transform_face(face, &translation, &mut shape));
+        top_faces.push(transform_face(&face, &translation, &mut shape));
     }
 
     for cycle in original.cycles().all() {
diff --git a/src/kernel/algorithms/transform.rs b/src/kernel/algorithms/transform.rs
index 0d937316f..1c2f63c4e 100644
--- a/src/kernel/algorithms/transform.rs
+++ b/src/kernel/algorithms/transform.rs
@@ -22,8 +22,8 @@ use crate::{
 pub fn transform_shape(mut original: Shape, transform: &Transform) -> Shape {
     let mut transformed = Shape::new();
 
-    for face in &original.faces().0 {
-        let face = transform_face(face, transform, &mut transformed);
+    for face in original.faces().all() {
+        let face = transform_face(&face, transform, &mut transformed);
         transformed.faces().0.push(face);
     }
 
diff --git a/src/kernel/shape/faces.rs b/src/kernel/shape/faces.rs
index 5a07deede..18d281e7d 100644
--- a/src/kernel/shape/faces.rs
+++ b/src/kernel/shape/faces.rs
@@ -9,6 +9,11 @@ use crate::{
 pub struct Faces(pub Vec<Face>);
 
 impl Faces {
+    /// Access an iterator over all faces
+    pub fn all(&self) -> impl Iterator<Item = Face> + '_ {
+        self.0.iter().cloned()
+    }
+
     pub fn triangles(
         &self,
         tolerance: Scalar,
diff --git a/src/kernel/shapes/difference_2d.rs b/src/kernel/shapes/difference_2d.rs
index 6325c5d86..a2f9be3f2 100644
--- a/src/kernel/shapes/difference_2d.rs
+++ b/src/kernel/shapes/difference_2d.rs
@@ -39,9 +39,14 @@ impl ToShape for fj::Difference2d {
         }
 
         *shape.faces() = {
-            let (a, b) = if a.faces().0.len() == 1 && b.faces().0.len() == 1 {
+            let (a, b) = if a.faces().all().count() == 1
+                && b.faces().all().count() == 1
+            {
                 // Can't panic. We just checked that length of `a` and `b` is 1.
-                (a.faces().0.pop().unwrap(), b.faces().0.pop().unwrap())
+                (
+                    a.faces().all().next().unwrap(),
+                    b.faces().all().next().unwrap(),
+                )
             } else {
                 // See issue:
                 // https://github.com/hannobraun/Fornjot/issues/95
diff --git a/src/kernel/shapes/union.rs b/src/kernel/shapes/union.rs
index 524e009e1..52167bf28 100644
--- a/src/kernel/shapes/union.rs
+++ b/src/kernel/shapes/union.rs
@@ -19,8 +19,8 @@ impl ToShape for fj::Union {
         // See issue:
         // https://github.com/hannobraun/Fornjot/issues/42
         let mut faces = Vec::new();
-        faces.extend(a.faces().0.clone());
-        faces.extend(b.faces().0.clone());
+        faces.extend(a.faces().all());
+        faces.extend(b.faces().all());
 
         *shape.faces() = Faces(faces);
 

From 3d48f7c2b65c99dc0cf0679431f5502cf1f98147 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Tue, 8 Mar 2022 13:47:45 +0100
Subject: [PATCH 10/21] Refactor

---
 src/kernel/shapes/circle.rs | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/src/kernel/shapes/circle.rs b/src/kernel/shapes/circle.rs
index c6e3ce36d..0366b4816 100644
--- a/src/kernel/shapes/circle.rs
+++ b/src/kernel/shapes/circle.rs
@@ -25,12 +25,13 @@ impl ToShape for fj::Circle {
             .add(Edge::circle(Scalar::from_f64(self.radius)));
         shape.cycles().add(Cycle { edges: vec![edge] });
 
+        let cycles = shape
+            .cycles()
+            .all()
+            .map(|handle| (*handle).clone())
+            .collect();
         *shape.faces() = Faces(vec![Face::Face {
-            cycles: shape
-                .cycles()
-                .all()
-                .map(|handle| (*handle).clone())
-                .collect(),
+            cycles,
             surface: Surface::x_y_plane(),
         }]);
 

From a90d132a3314381c48cb34172939515c790747bf Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Tue, 8 Mar 2022 13:50:06 +0100
Subject: [PATCH 11/21] Add `Faces::add`

---
 src/kernel/algorithms/sweep.rs     | 22 +++++++++++-----------
 src/kernel/algorithms/transform.rs |  2 +-
 src/kernel/shape/faces.rs          |  8 ++++++++
 src/kernel/shapes/circle.rs        |  6 +++---
 src/kernel/shapes/difference_2d.rs |  6 +++---
 src/kernel/shapes/sketch.rs        |  4 ++--
 src/kernel/shapes/union.rs         | 13 +++++++------
 7 files changed, 35 insertions(+), 26 deletions(-)

diff --git a/src/kernel/algorithms/sweep.rs b/src/kernel/algorithms/sweep.rs
index 0218c09ea..104e2ec4f 100644
--- a/src/kernel/algorithms/sweep.rs
+++ b/src/kernel/algorithms/sweep.rs
@@ -1,8 +1,5 @@
 use crate::{
-    kernel::{
-        shape::{faces::Faces, Shape},
-        topology::faces::Face,
-    },
+    kernel::{shape::Shape, topology::faces::Face},
     math::{Scalar, Transform, Vector},
 };
 
@@ -55,12 +52,15 @@ pub fn sweep_shape(
         side_faces.push(Face::Triangles(side_face));
     }
 
-    let mut faces = Vec::new();
-    faces.extend(bottom_faces);
-    faces.extend(top_faces);
-    faces.extend(side_faces);
-
-    *shape.faces() = Faces(faces);
+    for face in bottom_faces {
+        shape.faces().add(face);
+    }
+    for face in top_faces {
+        shape.faces().add(face);
+    }
+    for face in side_faces {
+        shape.faces().add(face);
+    }
 
     shape
 }
@@ -134,7 +134,7 @@ mod tests {
                 }],
             };
 
-            shape.faces().0.push(abc.clone());
+            shape.faces().add(abc.clone());
 
             Self { shape, face: abc }
         }
diff --git a/src/kernel/algorithms/transform.rs b/src/kernel/algorithms/transform.rs
index 1c2f63c4e..f737dce1e 100644
--- a/src/kernel/algorithms/transform.rs
+++ b/src/kernel/algorithms/transform.rs
@@ -24,7 +24,7 @@ pub fn transform_shape(mut original: Shape, transform: &Transform) -> Shape {
 
     for face in original.faces().all() {
         let face = transform_face(&face, transform, &mut transformed);
-        transformed.faces().0.push(face);
+        transformed.faces().add(face);
     }
 
     transformed
diff --git a/src/kernel/shape/faces.rs b/src/kernel/shape/faces.rs
index 18d281e7d..71ed8255b 100644
--- a/src/kernel/shape/faces.rs
+++ b/src/kernel/shape/faces.rs
@@ -4,11 +4,19 @@ use crate::{
     math::{Scalar, Triangle},
 };
 
+use super::handle::{Handle, Storage};
+
 /// The faces of a shape
 #[derive(Clone, Debug, Eq, PartialEq, Hash, Ord, PartialOrd)]
 pub struct Faces(pub Vec<Face>);
 
 impl Faces {
+    /// Add a face to the shape
+    pub fn add(&mut self, face: Face) -> Handle<Face> {
+        self.0.push(face.clone());
+        Storage::new(face).handle()
+    }
+
     /// Access an iterator over all faces
     pub fn all(&self) -> impl Iterator<Item = Face> + '_ {
         self.0.iter().cloned()
diff --git a/src/kernel/shapes/circle.rs b/src/kernel/shapes/circle.rs
index 0366b4816..3048af1c8 100644
--- a/src/kernel/shapes/circle.rs
+++ b/src/kernel/shapes/circle.rs
@@ -2,7 +2,7 @@ use crate::{
     debug::DebugInfo,
     kernel::{
         geometry::Surface,
-        shape::{faces::Faces, Shape},
+        shape::Shape,
         topology::{
             edges::{Cycle, Edge},
             faces::Face,
@@ -30,10 +30,10 @@ impl ToShape for fj::Circle {
             .all()
             .map(|handle| (*handle).clone())
             .collect();
-        *shape.faces() = Faces(vec![Face::Face {
+        shape.faces().add(Face::Face {
             cycles,
             surface: Surface::x_y_plane(),
-        }]);
+        });
 
         shape
     }
diff --git a/src/kernel/shapes/difference_2d.rs b/src/kernel/shapes/difference_2d.rs
index a2f9be3f2..80ff5dfc2 100644
--- a/src/kernel/shapes/difference_2d.rs
+++ b/src/kernel/shapes/difference_2d.rs
@@ -1,7 +1,7 @@
 use crate::{
     debug::DebugInfo,
     kernel::{
-        shape::{faces::Faces, Shape},
+        shape::Shape,
         topology::{edges::Cycle, faces::Face},
     },
     math::{Aabb, Scalar},
@@ -38,7 +38,7 @@ impl ToShape for fj::Difference2d {
             );
         }
 
-        *shape.faces() = {
+        {
             let (a, b) = if a.faces().all().count() == 1
                 && b.faces().all().count() == 1
             {
@@ -84,7 +84,7 @@ impl ToShape for fj::Difference2d {
             let mut cycles = a;
             cycles.extend(b);
 
-            Faces(vec![Face::Face { cycles, surface }])
+            shape.faces().add(Face::Face { cycles, surface });
         };
 
         shape
diff --git a/src/kernel/shapes/sketch.rs b/src/kernel/shapes/sketch.rs
index 9ca26f789..296604b4f 100644
--- a/src/kernel/shapes/sketch.rs
+++ b/src/kernel/shapes/sketch.rs
@@ -2,7 +2,7 @@ use crate::{
     debug::DebugInfo,
     kernel::{
         geometry::Surface,
-        shape::{faces::Faces, Shape},
+        shape::Shape,
         topology::{
             edges::{Cycle, Edge},
             faces::Face,
@@ -55,7 +55,7 @@ impl ToShape for fj::Sketch {
                 .collect(),
             surface: Surface::x_y_plane(),
         };
-        *shape.faces() = Faces(vec![face]);
+        shape.faces().add(face);
 
         shape
     }
diff --git a/src/kernel/shapes/union.rs b/src/kernel/shapes/union.rs
index 52167bf28..5b6a5cee3 100644
--- a/src/kernel/shapes/union.rs
+++ b/src/kernel/shapes/union.rs
@@ -1,6 +1,6 @@
 use crate::{
     debug::DebugInfo,
-    kernel::shape::{faces::Faces, Shape},
+    kernel::shape::Shape,
     math::{Aabb, Scalar},
 };
 
@@ -18,11 +18,12 @@ impl ToShape for fj::Union {
         //
         // See issue:
         // https://github.com/hannobraun/Fornjot/issues/42
-        let mut faces = Vec::new();
-        faces.extend(a.faces().all());
-        faces.extend(b.faces().all());
-
-        *shape.faces() = Faces(faces);
+        for face in a.faces().all() {
+            shape.faces().add(face);
+        }
+        for face in b.faces().all() {
+            shape.faces().add(face);
+        }
 
         shape
     }

From 07d6989e921317c36bdd31ac5564e9e56022e515 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Tue, 8 Mar 2022 13:52:02 +0100
Subject: [PATCH 12/21] Add `Faces::contains`

---
 src/kernel/algorithms/sweep.rs | 4 ++--
 src/kernel/shape/faces.rs      | 6 ++++++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/kernel/algorithms/sweep.rs b/src/kernel/algorithms/sweep.rs
index 104e2ec4f..bcd3ed1b1 100644
--- a/src/kernel/algorithms/sweep.rs
+++ b/src/kernel/algorithms/sweep.rs
@@ -95,8 +95,8 @@ mod tests {
         let top_face =
             Triangle::new([[0., 0., 1.], [1., 0., 1.], [0., 1., 1.]]).face;
 
-        assert!(swept.faces().0.contains(&bottom_face));
-        assert!(swept.faces().0.contains(&top_face));
+        assert!(swept.faces().contains(&bottom_face));
+        assert!(swept.faces().contains(&top_face));
 
         // Side faces are not tested, as those use triangle representation. The
         // plan is to start testing them, as they are transitioned to b-rep.
diff --git a/src/kernel/shape/faces.rs b/src/kernel/shape/faces.rs
index 71ed8255b..e5c648d02 100644
--- a/src/kernel/shape/faces.rs
+++ b/src/kernel/shape/faces.rs
@@ -17,6 +17,12 @@ impl Faces {
         Storage::new(face).handle()
     }
 
+    /// Check whether the shape contains a specific face
+    #[cfg(test)]
+    pub fn contains(&self, face: &Face) -> bool {
+        self.0.contains(face)
+    }
+
     /// Access an iterator over all faces
     pub fn all(&self) -> impl Iterator<Item = Face> + '_ {
         self.0.iter().cloned()

From e53c9655f17987a492cfd41b364db46cd3cb6e1f Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Tue, 8 Mar 2022 13:52:19 +0100
Subject: [PATCH 13/21] Make field of `Faces` private

---
 src/kernel/shape/faces.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/kernel/shape/faces.rs b/src/kernel/shape/faces.rs
index e5c648d02..bb5a54b77 100644
--- a/src/kernel/shape/faces.rs
+++ b/src/kernel/shape/faces.rs
@@ -8,7 +8,7 @@ use super::handle::{Handle, Storage};
 
 /// The faces of a shape
 #[derive(Clone, Debug, Eq, PartialEq, Hash, Ord, PartialOrd)]
-pub struct Faces(pub Vec<Face>);
+pub struct Faces(pub(super) Vec<Face>);
 
 impl Faces {
     /// Add a face to the shape

From 98c28517cc5a754309c8d6b4817071828bb8a41d Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Tue, 8 Mar 2022 13:53:32 +0100
Subject: [PATCH 14/21] Refactor

---
 src/kernel/algorithms/sweep.rs | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/kernel/algorithms/sweep.rs b/src/kernel/algorithms/sweep.rs
index bcd3ed1b1..8b006fe7b 100644
--- a/src/kernel/algorithms/sweep.rs
+++ b/src/kernel/algorithms/sweep.rs
@@ -70,7 +70,7 @@ mod tests {
     use crate::{
         kernel::{
             geometry::{surfaces::Swept, Surface},
-            shape::Shape,
+            shape::{handle::Handle, Shape},
             topology::{
                 edges::{Cycle, Edge},
                 faces::Face,
@@ -104,7 +104,7 @@ mod tests {
 
     pub struct Triangle {
         shape: Shape,
-        face: Face,
+        face: Handle<Face>,
     }
 
     impl Triangle {
@@ -134,9 +134,9 @@ mod tests {
                 }],
             };
 
-            shape.faces().add(abc.clone());
+            let face = shape.faces().add(abc);
 
-            Self { shape, face: abc }
+            Self { shape, face }
         }
     }
 }

From d7a8a2935b0ff379d9e73edfb8829a68d9bd126d Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Tue, 8 Mar 2022 13:55:22 +0100
Subject: [PATCH 15/21] Convert tuple struct into regular struct

---
 src/kernel/shape/faces.rs | 12 +++++++-----
 src/kernel/shape/mod.rs   |  2 +-
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/src/kernel/shape/faces.rs b/src/kernel/shape/faces.rs
index bb5a54b77..daf3101ca 100644
--- a/src/kernel/shape/faces.rs
+++ b/src/kernel/shape/faces.rs
@@ -8,24 +8,26 @@ use super::handle::{Handle, Storage};
 
 /// The faces of a shape
 #[derive(Clone, Debug, Eq, PartialEq, Hash, Ord, PartialOrd)]
-pub struct Faces(pub(super) Vec<Face>);
+pub struct Faces {
+    pub(super) faces: Vec<Face>,
+}
 
 impl Faces {
     /// Add a face to the shape
     pub fn add(&mut self, face: Face) -> Handle<Face> {
-        self.0.push(face.clone());
+        self.faces.push(face.clone());
         Storage::new(face).handle()
     }
 
     /// Check whether the shape contains a specific face
     #[cfg(test)]
     pub fn contains(&self, face: &Face) -> bool {
-        self.0.contains(face)
+        self.faces.contains(face)
     }
 
     /// Access an iterator over all faces
     pub fn all(&self) -> impl Iterator<Item = Face> + '_ {
-        self.0.iter().cloned()
+        self.faces.iter().cloned()
     }
 
     pub fn triangles(
@@ -34,7 +36,7 @@ impl Faces {
         out: &mut Vec<Triangle<3>>,
         debug_info: &mut DebugInfo,
     ) {
-        for face in &self.0 {
+        for face in &self.faces {
             face.triangles(tolerance, out, debug_info);
         }
     }
diff --git a/src/kernel/shape/mod.rs b/src/kernel/shape/mod.rs
index ad0c9f88f..ef9161c9b 100644
--- a/src/kernel/shape/mod.rs
+++ b/src/kernel/shape/mod.rs
@@ -43,7 +43,7 @@ impl Shape {
 
             vertices: VerticesInner::new(),
             cycles: CyclesInner::new(),
-            faces: Faces(Vec::new()),
+            faces: Faces { faces: Vec::new() },
         }
     }
 

From a932ce5fe8ce9b0c94800aca32e422e0bf156736 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Tue, 8 Mar 2022 13:58:24 +0100
Subject: [PATCH 16/21] Add type definition

---
 src/kernel/shape/faces.rs | 7 +++++--
 src/kernel/shape/mod.rs   | 3 ++-
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/src/kernel/shape/faces.rs b/src/kernel/shape/faces.rs
index daf3101ca..6d83bf02e 100644
--- a/src/kernel/shape/faces.rs
+++ b/src/kernel/shape/faces.rs
@@ -4,12 +4,15 @@ use crate::{
     math::{Scalar, Triangle},
 };
 
-use super::handle::{Handle, Storage};
+use super::{
+    handle::{Handle, Storage},
+    FacesInner,
+};
 
 /// The faces of a shape
 #[derive(Clone, Debug, Eq, PartialEq, Hash, Ord, PartialOrd)]
 pub struct Faces {
-    pub(super) faces: Vec<Face>,
+    pub(super) faces: FacesInner,
 }
 
 impl Faces {
diff --git a/src/kernel/shape/mod.rs b/src/kernel/shape/mod.rs
index ef9161c9b..13f308a1e 100644
--- a/src/kernel/shape/mod.rs
+++ b/src/kernel/shape/mod.rs
@@ -6,7 +6,7 @@ pub mod vertices;
 
 use crate::math::Scalar;
 
-use super::topology::{edges::Cycle, vertices::Vertex};
+use super::topology::{edges::Cycle, faces::Face, vertices::Vertex};
 
 use self::{
     cycles::Cycles, edges::Edges, faces::Faces, handle::Storage,
@@ -90,3 +90,4 @@ impl Shape {
 
 type VerticesInner = Vec<Storage<Vertex>>;
 type CyclesInner = Vec<Storage<Cycle>>;
+type FacesInner = Vec<Face>;

From 4d5a279f7152d7917b5aa624253d42d4619c1ab5 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Tue, 8 Mar 2022 14:00:11 +0100
Subject: [PATCH 17/21] Prevent write access to faces of `Shape`

---
 src/kernel/shape/faces.rs |  9 ++++-----
 src/kernel/shape/mod.rs   | 10 ++++++----
 2 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/src/kernel/shape/faces.rs b/src/kernel/shape/faces.rs
index 6d83bf02e..0c177317b 100644
--- a/src/kernel/shape/faces.rs
+++ b/src/kernel/shape/faces.rs
@@ -10,12 +10,11 @@ use super::{
 };
 
 /// The faces of a shape
-#[derive(Clone, Debug, Eq, PartialEq, Hash, Ord, PartialOrd)]
-pub struct Faces {
-    pub(super) faces: FacesInner,
+pub struct Faces<'r> {
+    pub(super) faces: &'r mut FacesInner,
 }
 
-impl Faces {
+impl Faces<'_> {
     /// Add a face to the shape
     pub fn add(&mut self, face: Face) -> Handle<Face> {
         self.faces.push(face.clone());
@@ -39,7 +38,7 @@ impl Faces {
         out: &mut Vec<Triangle<3>>,
         debug_info: &mut DebugInfo,
     ) {
-        for face in &self.faces {
+        for face in &*self.faces {
             face.triangles(tolerance, out, debug_info);
         }
     }
diff --git a/src/kernel/shape/mod.rs b/src/kernel/shape/mod.rs
index 13f308a1e..95e1786bd 100644
--- a/src/kernel/shape/mod.rs
+++ b/src/kernel/shape/mod.rs
@@ -29,7 +29,7 @@ pub struct Shape {
 
     vertices: VerticesInner,
     cycles: CyclesInner,
-    faces: Faces,
+    faces: FacesInner,
 }
 
 impl Shape {
@@ -43,7 +43,7 @@ impl Shape {
 
             vertices: VerticesInner::new(),
             cycles: CyclesInner::new(),
-            faces: Faces { faces: Vec::new() },
+            faces: FacesInner::new(),
         }
     }
 
@@ -83,8 +83,10 @@ impl Shape {
     }
 
     /// Access the shape's faces
-    pub fn faces(&mut self) -> &mut Faces {
-        &mut self.faces
+    pub fn faces(&mut self) -> Faces {
+        Faces {
+            faces: &mut self.faces,
+        }
     }
 }
 

From 2aeb7249924bae57f638bae0deaeafa71340de42 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Tue, 8 Mar 2022 14:13:06 +0100
Subject: [PATCH 18/21] Store faces in `Storage`

---
 src/kernel/algorithms/sweep.rs     |  2 +-
 src/kernel/shape/faces.rs          | 14 ++++++++-----
 src/kernel/shape/mod.rs            |  2 +-
 src/kernel/shapes/difference_2d.rs | 33 +++++++++++++++---------------
 src/kernel/shapes/union.rs         |  4 ++--
 5 files changed, 30 insertions(+), 25 deletions(-)

diff --git a/src/kernel/algorithms/sweep.rs b/src/kernel/algorithms/sweep.rs
index 8b006fe7b..cad604db5 100644
--- a/src/kernel/algorithms/sweep.rs
+++ b/src/kernel/algorithms/sweep.rs
@@ -53,7 +53,7 @@ pub fn sweep_shape(
     }
 
     for face in bottom_faces {
-        shape.faces().add(face);
+        shape.faces().add((*face).clone());
     }
     for face in top_faces {
         shape.faces().add(face);
diff --git a/src/kernel/shape/faces.rs b/src/kernel/shape/faces.rs
index 0c177317b..e1c8b3787 100644
--- a/src/kernel/shape/faces.rs
+++ b/src/kernel/shape/faces.rs
@@ -17,19 +17,23 @@ pub struct Faces<'r> {
 impl Faces<'_> {
     /// Add a face to the shape
     pub fn add(&mut self, face: Face) -> Handle<Face> {
-        self.faces.push(face.clone());
-        Storage::new(face).handle()
+        let storage = Storage::new(face);
+        let handle = storage.handle();
+
+        self.faces.push(storage);
+
+        handle
     }
 
     /// Check whether the shape contains a specific face
     #[cfg(test)]
     pub fn contains(&self, face: &Face) -> bool {
-        self.faces.contains(face)
+        self.faces.contains(&Storage::new(face.clone()))
     }
 
     /// Access an iterator over all faces
-    pub fn all(&self) -> impl Iterator<Item = Face> + '_ {
-        self.faces.iter().cloned()
+    pub fn all(&self) -> impl Iterator<Item = Handle<Face>> + '_ {
+        self.faces.iter().map(|storage| storage.handle())
     }
 
     pub fn triangles(
diff --git a/src/kernel/shape/mod.rs b/src/kernel/shape/mod.rs
index 95e1786bd..1c37ddcfb 100644
--- a/src/kernel/shape/mod.rs
+++ b/src/kernel/shape/mod.rs
@@ -92,4 +92,4 @@ impl Shape {
 
 type VerticesInner = Vec<Storage<Vertex>>;
 type CyclesInner = Vec<Storage<Cycle>>;
-type FacesInner = Vec<Face>;
+type FacesInner = Vec<Storage<Face>>;
diff --git a/src/kernel/shapes/difference_2d.rs b/src/kernel/shapes/difference_2d.rs
index 80ff5dfc2..c1eac9f4c 100644
--- a/src/kernel/shapes/difference_2d.rs
+++ b/src/kernel/shapes/difference_2d.rs
@@ -56,22 +56,23 @@ impl ToShape for fj::Difference2d {
                 );
             };
 
-            let (a, b, surface_a, surface_b) = match (a, b) {
-                (
-                    Face::Face {
-                        cycles: a,
-                        surface: surface_a,
-                    },
-                    Face::Face {
-                        cycles: b,
-                        surface: surface_b,
-                    },
-                ) => (a, b, surface_a, surface_b),
-                _ => {
-                    // None of the 2D types still use the triangles representation.
-                    unreachable!()
-                }
-            };
+            let (a, b, surface_a, surface_b) =
+                match ((*a).clone(), (*b).clone()) {
+                    (
+                        Face::Face {
+                            cycles: a,
+                            surface: surface_a,
+                        },
+                        Face::Face {
+                            cycles: b,
+                            surface: surface_b,
+                        },
+                    ) => (a, b, surface_a, surface_b),
+                    _ => {
+                        // None of the 2D types still use the triangles representation.
+                        unreachable!()
+                    }
+                };
 
             assert!(
                 surface_a == surface_b,
diff --git a/src/kernel/shapes/union.rs b/src/kernel/shapes/union.rs
index 5b6a5cee3..8147510fc 100644
--- a/src/kernel/shapes/union.rs
+++ b/src/kernel/shapes/union.rs
@@ -19,10 +19,10 @@ impl ToShape for fj::Union {
         // See issue:
         // https://github.com/hannobraun/Fornjot/issues/42
         for face in a.faces().all() {
-            shape.faces().add(face);
+            shape.faces().add((*face).clone());
         }
         for face in b.faces().all() {
-            shape.faces().add(face);
+            shape.faces().add((*face).clone());
         }
 
         shape

From 14e304346de0065e54849bd72d51b542fad9f457 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Tue, 8 Mar 2022 14:13:24 +0100
Subject: [PATCH 19/21] Fix return type of `Cycles::all`

---
 src/kernel/shape/cycles.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/kernel/shape/cycles.rs b/src/kernel/shape/cycles.rs
index 83c9315b5..6a06295cf 100644
--- a/src/kernel/shape/cycles.rs
+++ b/src/kernel/shape/cycles.rs
@@ -29,7 +29,7 @@ impl Cycles<'_> {
     }
 
     /// Access an iterator over all cycles
-    pub fn all(&self) -> impl Iterator<Item = Storage<Cycle>> + '_ {
-        self.cycles.iter().cloned()
+    pub fn all(&self) -> impl Iterator<Item = Handle<Cycle>> + '_ {
+        self.cycles.iter().map(|storage| storage.handle())
     }
 }

From dddcc8c3774d8ede486c0894403765b0f9314721 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Tue, 8 Mar 2022 14:13:48 +0100
Subject: [PATCH 20/21] Update comment

---
 src/kernel/shapes/difference_2d.rs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/kernel/shapes/difference_2d.rs b/src/kernel/shapes/difference_2d.rs
index c1eac9f4c..fc1113902 100644
--- a/src/kernel/shapes/difference_2d.rs
+++ b/src/kernel/shapes/difference_2d.rs
@@ -69,7 +69,8 @@ impl ToShape for fj::Difference2d {
                         },
                     ) => (a, b, surface_a, surface_b),
                     _ => {
-                        // None of the 2D types still use the triangles representation.
+                        // None of the 2D types still use triangle
+                        // representation.
                         unreachable!()
                     }
                 };

From 9a88774fffbf6996ee1f01d6ba2ed06f2303f4ef Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Tue, 8 Mar 2022 14:14:54 +0100
Subject: [PATCH 21/21] Remove outdated implementation note

---
 src/kernel/shape/mod.rs | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/src/kernel/shape/mod.rs b/src/kernel/shape/mod.rs
index 1c37ddcfb..265fab1a4 100644
--- a/src/kernel/shape/mod.rs
+++ b/src/kernel/shape/mod.rs
@@ -14,12 +14,6 @@ use self::{
 };
 
 /// The boundary representation of a shape
-///
-/// # Implementation note
-///
-/// The goal for `Shape` is to enforce full self-consistency, through the API it
-/// provides. Steps have been made in that direction, but right now, the API is
-/// still full of holes, forcing callers to just be careful for the time being.
 #[derive(Clone, Debug)]
 pub struct Shape {
     /// The minimum distance between two vertices