From 7265180f87891a3cb39168791cdba04ed3dd3fa3 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 11:25:04 +0100
Subject: [PATCH 01/27] Add `Event` trait

---
 crates/fj-core/src/layers/layer.rs | 3 +++
 crates/fj-core/src/layers/mod.rs   | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/crates/fj-core/src/layers/layer.rs b/crates/fj-core/src/layers/layer.rs
index efa1efcbe..32a106fc3 100644
--- a/crates/fj-core/src/layers/layer.rs
+++ b/crates/fj-core/src/layers/layer.rs
@@ -95,3 +95,6 @@ pub trait State {
     /// [`State::decide`], and encoded into the event.
     fn evolve(&mut self, event: &Self::Event);
 }
+
+/// An event that encodes a change to a layer's state
+pub trait Event<S> {}
diff --git a/crates/fj-core/src/layers/mod.rs b/crates/fj-core/src/layers/mod.rs
index 953ff94f3..4c78af2ed 100644
--- a/crates/fj-core/src/layers/mod.rs
+++ b/crates/fj-core/src/layers/mod.rs
@@ -9,6 +9,6 @@ mod layer;
 mod layers;
 
 pub use self::{
-    layer::{Layer, State},
+    layer::{Event, Layer, State},
     layers::Layers,
 };

From 9a9877df8f13f672ba279f010b64f4d6325a4cdc Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 11:25:19 +0100
Subject: [PATCH 02/27] Require `State` to be `Sized`

---
 crates/fj-core/src/layers/layer.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/crates/fj-core/src/layers/layer.rs b/crates/fj-core/src/layers/layer.rs
index 32a106fc3..37fb6ef27 100644
--- a/crates/fj-core/src/layers/layer.rs
+++ b/crates/fj-core/src/layers/layer.rs
@@ -67,7 +67,7 @@ where
 /// the consumer of this trait's API.
 ///
 /// See [`Layer`] for a more detailed explanation.
-pub trait State {
+pub trait State: Sized {
     /// A command that encodes a request to update the state
     ///
     /// Commands are processed by [`State::decide`].

From ce95d0b3615ebd931acc6f99cbc4affb7f769452 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 11:25:40 +0100
Subject: [PATCH 03/27] Require `State::Event` to implement `Event`

---
 crates/fj-core/src/layers/layer.rs      | 2 +-
 crates/fj-core/src/layers/objects.rs    | 4 +++-
 crates/fj-core/src/layers/validation.rs | 4 +++-
 3 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/crates/fj-core/src/layers/layer.rs b/crates/fj-core/src/layers/layer.rs
index 37fb6ef27..9ef337889 100644
--- a/crates/fj-core/src/layers/layer.rs
+++ b/crates/fj-core/src/layers/layer.rs
@@ -77,7 +77,7 @@ pub trait State: Sized {
     ///
     /// Events are produced by [`State::decide`] and processed by
     /// [`State::evolve`].
-    type Event;
+    type Event: Event<Self>;
 
     /// Decide how to react to the provided command
     ///
diff --git a/crates/fj-core/src/layers/objects.rs b/crates/fj-core/src/layers/objects.rs
index 4d6828ab4..a1f025928 100644
--- a/crates/fj-core/src/layers/objects.rs
+++ b/crates/fj-core/src/layers/objects.rs
@@ -5,7 +5,7 @@ use crate::{
     validate::Validation,
 };
 
-use super::{Layer, State};
+use super::{Event, Layer, State};
 
 impl Layer<Objects> {
     /// Insert and object into the stores
@@ -60,3 +60,5 @@ pub enum ObjectsEvent {
         object: AnyObject<AboutToBeStored>,
     },
 }
+
+impl Event<Objects> for ObjectsEvent {}
diff --git a/crates/fj-core/src/layers/validation.rs b/crates/fj-core/src/layers/validation.rs
index b826045e4..3e5836a0c 100644
--- a/crates/fj-core/src/layers/validation.rs
+++ b/crates/fj-core/src/layers/validation.rs
@@ -5,7 +5,7 @@ use crate::{
     validate::{Validation, ValidationError, ValidationErrors},
 };
 
-use super::{objects::ObjectsEvent, Layer, State};
+use super::{objects::ObjectsEvent, Event, Layer, State};
 
 impl Layer<Validation> {
     /// Handler for [`ObjectsEvent`]
@@ -80,3 +80,5 @@ pub enum ValidationEvent {
         err: ValidationError,
     },
 }
+
+impl Event<Validation> for ValidationEvent {}

From 692b325bb2b260365f8b08bc5685bf512b73228d Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 11:36:02 +0100
Subject: [PATCH 04/27] Convert `State::evolve` into `Event::evolve`

---
 crates/fj-core/src/layers/layer.rs      | 14 +++++++-------
 crates/fj-core/src/layers/objects.rs    | 12 ++++++------
 crates/fj-core/src/layers/validation.rs | 18 +++++++++---------
 3 files changed, 22 insertions(+), 22 deletions(-)

diff --git a/crates/fj-core/src/layers/layer.rs b/crates/fj-core/src/layers/layer.rs
index 9ef337889..6485fef12 100644
--- a/crates/fj-core/src/layers/layer.rs
+++ b/crates/fj-core/src/layers/layer.rs
@@ -34,7 +34,7 @@ impl<S: State> Layer<S> {
         self.state.decide(command, events);
 
         for event in events {
-            self.state.evolve(event);
+            event.evolve(&mut self.state);
         }
     }
 
@@ -76,7 +76,7 @@ pub trait State: Sized {
     /// An event that encodes a change to the state
     ///
     /// Events are produced by [`State::decide`] and processed by
-    /// [`State::evolve`].
+    /// [`Event::evolve`].
     type Event: Event<Self>;
 
     /// Decide how to react to the provided command
@@ -84,8 +84,11 @@ pub trait State: Sized {
     /// If the command must result in changes to the state, any number of events
     /// that describe these state changes can be produced.
     fn decide(&self, command: Self::Command, events: &mut Vec<Self::Event>);
+}
 
-    /// Evolve the state according to the provided event
+/// An event that encodes a change to a layer's state
+pub trait Event<S> {
+    /// Evolve the provided state
     ///
     /// This is the only method that gets mutable access to the state, making
     /// sure that all changes to the state are captured as events.
@@ -93,8 +96,5 @@ pub trait State: Sized {
     /// Implementations of this method are supposed to be relatively dumb. Any
     /// decisions that go into updating the state should be made in
     /// [`State::decide`], and encoded into the event.
-    fn evolve(&mut self, event: &Self::Event);
+    fn evolve(&self, state: &mut S);
 }
-
-/// An event that encodes a change to a layer's state
-pub trait Event<S> {}
diff --git a/crates/fj-core/src/layers/objects.rs b/crates/fj-core/src/layers/objects.rs
index a1f025928..f3677c933 100644
--- a/crates/fj-core/src/layers/objects.rs
+++ b/crates/fj-core/src/layers/objects.rs
@@ -31,11 +31,6 @@ impl State for Objects {
         let ObjectsCommand::InsertObject { object } = command;
         events.push(ObjectsEvent::InsertObject { object });
     }
-
-    fn evolve(&mut self, event: &Self::Event) {
-        let ObjectsEvent::InsertObject { object } = event;
-        object.clone().insert(self);
-    }
 }
 
 /// Command for `Layer<Objects>`
@@ -61,4 +56,9 @@ pub enum ObjectsEvent {
     },
 }
 
-impl Event<Objects> for ObjectsEvent {}
+impl Event<Objects> for ObjectsEvent {
+    fn evolve(&self, state: &mut Objects) {
+        let ObjectsEvent::InsertObject { object } = self;
+        object.clone().insert(state);
+    }
+}
diff --git a/crates/fj-core/src/layers/validation.rs b/crates/fj-core/src/layers/validation.rs
index 3e5836a0c..e26d4d0a1 100644
--- a/crates/fj-core/src/layers/validation.rs
+++ b/crates/fj-core/src/layers/validation.rs
@@ -49,14 +49,6 @@ impl State for Validation {
             }
         }
     }
-
-    fn evolve(&mut self, event: &Self::Event) {
-        match event {
-            ValidationEvent::ValidationFailed { object, err } => {
-                self.errors.insert(object.id(), err.clone());
-            }
-        }
-    }
 }
 
 /// Command for `Layer<Validation>`
@@ -81,4 +73,12 @@ pub enum ValidationEvent {
     },
 }
 
-impl Event<Validation> for ValidationEvent {}
+impl Event<Validation> for ValidationEvent {
+    fn evolve(&self, state: &mut Validation) {
+        match self {
+            ValidationEvent::ValidationFailed { object, err } => {
+                state.errors.insert(object.id(), err.clone());
+            }
+        }
+    }
+}

From 7484a10b1722b871b2a90ba161ecf63ff168db2e Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 11:36:34 +0100
Subject: [PATCH 05/27] Refactor to simplify

---
 crates/fj-core/src/layers/validation.rs | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/crates/fj-core/src/layers/validation.rs b/crates/fj-core/src/layers/validation.rs
index e26d4d0a1..b583a98a9 100644
--- a/crates/fj-core/src/layers/validation.rs
+++ b/crates/fj-core/src/layers/validation.rs
@@ -75,10 +75,7 @@ pub enum ValidationEvent {
 
 impl Event<Validation> for ValidationEvent {
     fn evolve(&self, state: &mut Validation) {
-        match self {
-            ValidationEvent::ValidationFailed { object, err } => {
-                state.errors.insert(object.id(), err.clone());
-            }
-        }
+        let ValidationEvent::ValidationFailed { object, err } = self;
+        state.errors.insert(object.id(), err.clone());
     }
 }

From 310b4372d42bd789a779160f9b8e5378ce39bb51 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 11:39:03 +0100
Subject: [PATCH 06/27] Simplify `ValidationEvent`

---
 crates/fj-core/src/layers/validation.rs | 18 +++++++-----------
 1 file changed, 7 insertions(+), 11 deletions(-)

diff --git a/crates/fj-core/src/layers/validation.rs b/crates/fj-core/src/layers/validation.rs
index b583a98a9..dcf130600 100644
--- a/crates/fj-core/src/layers/validation.rs
+++ b/crates/fj-core/src/layers/validation.rs
@@ -41,7 +41,7 @@ impl State for Validation {
                 object.validate_with_config(&self.config, &mut errors);
 
                 for err in errors {
-                    events.push(ValidationEvent::ValidationFailed {
+                    events.push(ValidationEvent {
                         object: object.clone(),
                         err,
                     });
@@ -62,20 +62,16 @@ pub enum ValidationCommand {
 
 /// Event produced by `Layer<Validation>`
 #[derive(Clone)]
-pub enum ValidationEvent {
-    /// Validation of an object failed
-    ValidationFailed {
-        /// The object for which validation failed
-        object: AnyObject<Stored>,
+pub struct ValidationEvent {
+    /// The object for which validation failed
+    pub object: AnyObject<Stored>,
 
-        /// The validation error
-        err: ValidationError,
-    },
+    /// The validation error
+    pub err: ValidationError,
 }
 
 impl Event<Validation> for ValidationEvent {
     fn evolve(&self, state: &mut Validation) {
-        let ValidationEvent::ValidationFailed { object, err } = self;
-        state.errors.insert(object.id(), err.clone());
+        state.errors.insert(self.object.id(), self.err.clone());
     }
 }

From 3154f997f84473eafdc7d782c912b629f579b835 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 11:39:18 +0100
Subject: [PATCH 07/27] Update documentation of `ValidationEvent`

---
 crates/fj-core/src/layers/validation.rs | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/crates/fj-core/src/layers/validation.rs b/crates/fj-core/src/layers/validation.rs
index dcf130600..fc4dd30a6 100644
--- a/crates/fj-core/src/layers/validation.rs
+++ b/crates/fj-core/src/layers/validation.rs
@@ -60,7 +60,9 @@ pub enum ValidationCommand {
     },
 }
 
-/// Event produced by `Layer<Validation>`
+/// Validation of an object failed
+///
+/// Event produced by `Layer<Validation>`.
 #[derive(Clone)]
 pub struct ValidationEvent {
     /// The object for which validation failed

From 5b5a8024050f5fddc875f63c79108d9f5a6cd0ed Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 11:39:41 +0100
Subject: [PATCH 08/27] Rename `ValidationEvent` to `ValidationFailed`

---
 crates/fj-core/src/layers/validation.rs | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/crates/fj-core/src/layers/validation.rs b/crates/fj-core/src/layers/validation.rs
index fc4dd30a6..056ff718d 100644
--- a/crates/fj-core/src/layers/validation.rs
+++ b/crates/fj-core/src/layers/validation.rs
@@ -31,7 +31,7 @@ impl Layer<Validation> {
 
 impl State for Validation {
     type Command = ValidationCommand;
-    type Event = ValidationEvent;
+    type Event = ValidationFailed;
 
     fn decide(&self, command: Self::Command, events: &mut Vec<Self::Event>) {
         let mut errors = Vec::new();
@@ -41,7 +41,7 @@ impl State for Validation {
                 object.validate_with_config(&self.config, &mut errors);
 
                 for err in errors {
-                    events.push(ValidationEvent {
+                    events.push(ValidationFailed {
                         object: object.clone(),
                         err,
                     });
@@ -64,7 +64,7 @@ pub enum ValidationCommand {
 ///
 /// Event produced by `Layer<Validation>`.
 #[derive(Clone)]
-pub struct ValidationEvent {
+pub struct ValidationFailed {
     /// The object for which validation failed
     pub object: AnyObject<Stored>,
 
@@ -72,7 +72,7 @@ pub struct ValidationEvent {
     pub err: ValidationError,
 }
 
-impl Event<Validation> for ValidationEvent {
+impl Event<Validation> for ValidationFailed {
     fn evolve(&self, state: &mut Validation) {
         state.errors.insert(self.object.id(), self.err.clone());
     }

From 00b54dc2c5b50a84bde5f5575b6e2652a2fb236d Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 11:41:57 +0100
Subject: [PATCH 09/27] Simplify `ObjectsEvent`

---
 crates/fj-core/src/layers/objects.rs    | 14 +++++---------
 crates/fj-core/src/layers/validation.rs |  3 +--
 2 files changed, 6 insertions(+), 11 deletions(-)

diff --git a/crates/fj-core/src/layers/objects.rs b/crates/fj-core/src/layers/objects.rs
index f3677c933..a2b06974c 100644
--- a/crates/fj-core/src/layers/objects.rs
+++ b/crates/fj-core/src/layers/objects.rs
@@ -29,7 +29,7 @@ impl State for Objects {
 
     fn decide(&self, command: Self::Command, events: &mut Vec<Self::Event>) {
         let ObjectsCommand::InsertObject { object } = command;
-        events.push(ObjectsEvent::InsertObject { object });
+        events.push(ObjectsEvent { object });
     }
 }
 
@@ -48,17 +48,13 @@ pub enum ObjectsCommand {
 
 /// Event produced by `Layer<Objects>`
 #[derive(Clone, Debug)]
-pub enum ObjectsEvent {
-    /// Insert an object into the stores
-    InsertObject {
-        /// The object to insert
-        object: AnyObject<AboutToBeStored>,
-    },
+pub struct ObjectsEvent {
+    /// The object to insert
+    pub object: AnyObject<AboutToBeStored>,
 }
 
 impl Event<Objects> for ObjectsEvent {
     fn evolve(&self, state: &mut Objects) {
-        let ObjectsEvent::InsertObject { object } = self;
-        object.clone().insert(state);
+        self.object.clone().insert(state);
     }
 }
diff --git a/crates/fj-core/src/layers/validation.rs b/crates/fj-core/src/layers/validation.rs
index 056ff718d..579764902 100644
--- a/crates/fj-core/src/layers/validation.rs
+++ b/crates/fj-core/src/layers/validation.rs
@@ -10,9 +10,8 @@ use super::{objects::ObjectsEvent, Event, Layer, State};
 impl Layer<Validation> {
     /// Handler for [`ObjectsEvent`]
     pub fn on_objects_event(&mut self, event: ObjectsEvent) {
-        let ObjectsEvent::InsertObject { object } = event;
         let command = ValidationCommand::ValidateObject {
-            object: object.into(),
+            object: event.object.into(),
         };
         self.process(command, &mut Vec::new());
     }

From f03cd500d58c6da88943007a22a292fbdaab019e Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 11:42:10 +0100
Subject: [PATCH 10/27] Update documentation of `ObjectsEvent`

---
 crates/fj-core/src/layers/objects.rs | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/crates/fj-core/src/layers/objects.rs b/crates/fj-core/src/layers/objects.rs
index a2b06974c..f5e41611d 100644
--- a/crates/fj-core/src/layers/objects.rs
+++ b/crates/fj-core/src/layers/objects.rs
@@ -46,7 +46,9 @@ pub enum ObjectsCommand {
     },
 }
 
-/// Event produced by `Layer<Objects>`
+/// Insert an object into the stores
+///
+/// Event produced by `Layer<Objects>`.
 #[derive(Clone, Debug)]
 pub struct ObjectsEvent {
     /// The object to insert

From 7beaa998830305f40afc962deb4298877272da8d Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 11:43:03 +0100
Subject: [PATCH 11/27] Rename `ObjectsEvent` to `InsertObject`

---
 crates/fj-core/src/layers/objects.rs    | 8 ++++----
 crates/fj-core/src/layers/validation.rs | 6 +++---
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/crates/fj-core/src/layers/objects.rs b/crates/fj-core/src/layers/objects.rs
index f5e41611d..25f649f62 100644
--- a/crates/fj-core/src/layers/objects.rs
+++ b/crates/fj-core/src/layers/objects.rs
@@ -25,11 +25,11 @@ impl Layer<Objects> {
 
 impl State for Objects {
     type Command = ObjectsCommand;
-    type Event = ObjectsEvent;
+    type Event = InsertObject;
 
     fn decide(&self, command: Self::Command, events: &mut Vec<Self::Event>) {
         let ObjectsCommand::InsertObject { object } = command;
-        events.push(ObjectsEvent { object });
+        events.push(InsertObject { object });
     }
 }
 
@@ -50,12 +50,12 @@ pub enum ObjectsCommand {
 ///
 /// Event produced by `Layer<Objects>`.
 #[derive(Clone, Debug)]
-pub struct ObjectsEvent {
+pub struct InsertObject {
     /// The object to insert
     pub object: AnyObject<AboutToBeStored>,
 }
 
-impl Event<Objects> for ObjectsEvent {
+impl Event<Objects> for InsertObject {
     fn evolve(&self, state: &mut Objects) {
         self.object.clone().insert(state);
     }
diff --git a/crates/fj-core/src/layers/validation.rs b/crates/fj-core/src/layers/validation.rs
index 579764902..2c05e561c 100644
--- a/crates/fj-core/src/layers/validation.rs
+++ b/crates/fj-core/src/layers/validation.rs
@@ -5,11 +5,11 @@ use crate::{
     validate::{Validation, ValidationError, ValidationErrors},
 };
 
-use super::{objects::ObjectsEvent, Event, Layer, State};
+use super::{objects::InsertObject, Event, Layer, State};
 
 impl Layer<Validation> {
-    /// Handler for [`ObjectsEvent`]
-    pub fn on_objects_event(&mut self, event: ObjectsEvent) {
+    /// Handler for [`InsertObject`]
+    pub fn on_objects_event(&mut self, event: InsertObject) {
         let command = ValidationCommand::ValidateObject {
             object: event.object.into(),
         };

From f088fec63accec05b31b0317005d3b7c68c638a2 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 12:09:46 +0100
Subject: [PATCH 12/27] Update method name

---
 crates/fj-core/src/layers/objects.rs    | 2 +-
 crates/fj-core/src/layers/validation.rs | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/crates/fj-core/src/layers/objects.rs b/crates/fj-core/src/layers/objects.rs
index 25f649f62..844909fb4 100644
--- a/crates/fj-core/src/layers/objects.rs
+++ b/crates/fj-core/src/layers/objects.rs
@@ -18,7 +18,7 @@ impl Layer<Objects> {
         self.process(ObjectsCommand::InsertObject { object }, &mut events);
 
         for event in events {
-            validation.on_objects_event(event);
+            validation.on_insert_object(event);
         }
     }
 }
diff --git a/crates/fj-core/src/layers/validation.rs b/crates/fj-core/src/layers/validation.rs
index 2c05e561c..984a399bd 100644
--- a/crates/fj-core/src/layers/validation.rs
+++ b/crates/fj-core/src/layers/validation.rs
@@ -9,7 +9,7 @@ use super::{objects::InsertObject, Event, Layer, State};
 
 impl Layer<Validation> {
     /// Handler for [`InsertObject`]
-    pub fn on_objects_event(&mut self, event: InsertObject) {
+    pub fn on_insert_object(&mut self, event: InsertObject) {
         let command = ValidationCommand::ValidateObject {
             object: event.object.into(),
         };

From 2915051e5bc816cd90b697214cd389812b9d2e6a Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 11:48:30 +0100
Subject: [PATCH 13/27] Add `Command` trait

---
 crates/fj-core/src/layers/layer.rs | 3 +++
 crates/fj-core/src/layers/mod.rs   | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/crates/fj-core/src/layers/layer.rs b/crates/fj-core/src/layers/layer.rs
index 6485fef12..511eb7b9f 100644
--- a/crates/fj-core/src/layers/layer.rs
+++ b/crates/fj-core/src/layers/layer.rs
@@ -86,6 +86,9 @@ pub trait State: Sized {
     fn decide(&self, command: Self::Command, events: &mut Vec<Self::Event>);
 }
 
+/// A command that encodes a request to update a layer's state
+pub trait Command<S: State> {}
+
 /// An event that encodes a change to a layer's state
 pub trait Event<S> {
     /// Evolve the provided state
diff --git a/crates/fj-core/src/layers/mod.rs b/crates/fj-core/src/layers/mod.rs
index 4c78af2ed..d077897fa 100644
--- a/crates/fj-core/src/layers/mod.rs
+++ b/crates/fj-core/src/layers/mod.rs
@@ -9,6 +9,6 @@ mod layer;
 mod layers;
 
 pub use self::{
-    layer::{Event, Layer, State},
+    layer::{Command, Event, Layer, State},
     layers::Layers,
 };

From 9555364661c855d7d937b314a9124916923c1e1b Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 11:54:39 +0100
Subject: [PATCH 14/27] Implement `Command` for layer change commands

---
 crates/fj-core/src/layers/layer.rs      | 2 +-
 crates/fj-core/src/layers/objects.rs    | 4 +++-
 crates/fj-core/src/layers/validation.rs | 4 +++-
 3 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/crates/fj-core/src/layers/layer.rs b/crates/fj-core/src/layers/layer.rs
index 511eb7b9f..d4d8fd0a3 100644
--- a/crates/fj-core/src/layers/layer.rs
+++ b/crates/fj-core/src/layers/layer.rs
@@ -71,7 +71,7 @@ pub trait State: Sized {
     /// A command that encodes a request to update the state
     ///
     /// Commands are processed by [`State::decide`].
-    type Command;
+    type Command: Command<Self>;
 
     /// An event that encodes a change to the state
     ///
diff --git a/crates/fj-core/src/layers/objects.rs b/crates/fj-core/src/layers/objects.rs
index 844909fb4..22a58c138 100644
--- a/crates/fj-core/src/layers/objects.rs
+++ b/crates/fj-core/src/layers/objects.rs
@@ -5,7 +5,7 @@ use crate::{
     validate::Validation,
 };
 
-use super::{Event, Layer, State};
+use super::{Command, Event, Layer, State};
 
 impl Layer<Objects> {
     /// Insert and object into the stores
@@ -46,6 +46,8 @@ pub enum ObjectsCommand {
     },
 }
 
+impl Command<Objects> for ObjectsCommand {}
+
 /// Insert an object into the stores
 ///
 /// Event produced by `Layer<Objects>`.
diff --git a/crates/fj-core/src/layers/validation.rs b/crates/fj-core/src/layers/validation.rs
index 984a399bd..90673746f 100644
--- a/crates/fj-core/src/layers/validation.rs
+++ b/crates/fj-core/src/layers/validation.rs
@@ -5,7 +5,7 @@ use crate::{
     validate::{Validation, ValidationError, ValidationErrors},
 };
 
-use super::{objects::InsertObject, Event, Layer, State};
+use super::{objects::InsertObject, Command, Event, Layer, State};
 
 impl Layer<Validation> {
     /// Handler for [`InsertObject`]
@@ -59,6 +59,8 @@ pub enum ValidationCommand {
     },
 }
 
+impl Command<Validation> for ValidationCommand {}
+
 /// Validation of an object failed
 ///
 /// Event produced by `Layer<Validation>`.

From 0ae7979ba897fcc73a11930a10bd21fc1dc770d8 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 11:58:48 +0100
Subject: [PATCH 15/27] Convert `State::decide` into `Command::decide`

---
 crates/fj-core/src/layers/layer.rs      | 18 +++++++-------
 crates/fj-core/src/layers/objects.rs    | 12 +++++-----
 crates/fj-core/src/layers/validation.rs | 32 ++++++++++++++-----------
 3 files changed, 33 insertions(+), 29 deletions(-)

diff --git a/crates/fj-core/src/layers/layer.rs b/crates/fj-core/src/layers/layer.rs
index d4d8fd0a3..1ffc0e94a 100644
--- a/crates/fj-core/src/layers/layer.rs
+++ b/crates/fj-core/src/layers/layer.rs
@@ -31,7 +31,7 @@ impl<S: State> Layer<S> {
     /// The command is processed synchronously. When this method returns, the
     /// state has been updated.
     pub fn process(&mut self, command: S::Command, events: &mut Vec<S::Event>) {
-        self.state.decide(command, events);
+        command.decide(&self.state, events);
 
         for event in events {
             event.evolve(&mut self.state);
@@ -70,25 +70,25 @@ where
 pub trait State: Sized {
     /// A command that encodes a request to update the state
     ///
-    /// Commands are processed by [`State::decide`].
+    /// Commands are processed by [`Command::decide`].
     type Command: Command<Self>;
 
     /// An event that encodes a change to the state
     ///
-    /// Events are produced by [`State::decide`] and processed by
+    /// Events are produced by [`Command::decide`] and processed by
     /// [`Event::evolve`].
     type Event: Event<Self>;
+}
 
-    /// Decide how to react to the provided command
+/// A command that encodes a request to update a layer's state
+pub trait Command<S: State> {
+    /// Decide which events to produce, given the command and provided state
     ///
     /// If the command must result in changes to the state, any number of events
     /// that describe these state changes can be produced.
-    fn decide(&self, command: Self::Command, events: &mut Vec<Self::Event>);
+    fn decide(self, state: &S, events: &mut Vec<S::Event>);
 }
 
-/// A command that encodes a request to update a layer's state
-pub trait Command<S: State> {}
-
 /// An event that encodes a change to a layer's state
 pub trait Event<S> {
     /// Evolve the provided state
@@ -98,6 +98,6 @@ pub trait Event<S> {
     ///
     /// Implementations of this method are supposed to be relatively dumb. Any
     /// decisions that go into updating the state should be made in
-    /// [`State::decide`], and encoded into the event.
+    /// [`Command::decide`], and encoded into the event.
     fn evolve(&self, state: &mut S);
 }
diff --git a/crates/fj-core/src/layers/objects.rs b/crates/fj-core/src/layers/objects.rs
index 22a58c138..d45547645 100644
--- a/crates/fj-core/src/layers/objects.rs
+++ b/crates/fj-core/src/layers/objects.rs
@@ -26,11 +26,6 @@ impl Layer<Objects> {
 impl State for Objects {
     type Command = ObjectsCommand;
     type Event = InsertObject;
-
-    fn decide(&self, command: Self::Command, events: &mut Vec<Self::Event>) {
-        let ObjectsCommand::InsertObject { object } = command;
-        events.push(InsertObject { object });
-    }
 }
 
 /// Command for `Layer<Objects>`
@@ -46,7 +41,12 @@ pub enum ObjectsCommand {
     },
 }
 
-impl Command<Objects> for ObjectsCommand {}
+impl Command<Objects> for ObjectsCommand {
+    fn decide(self, _: &Objects, events: &mut Vec<<Objects as State>::Event>) {
+        let ObjectsCommand::InsertObject { object } = self;
+        events.push(InsertObject { object });
+    }
+}
 
 /// Insert an object into the stores
 ///
diff --git a/crates/fj-core/src/layers/validation.rs b/crates/fj-core/src/layers/validation.rs
index 90673746f..618fd1b07 100644
--- a/crates/fj-core/src/layers/validation.rs
+++ b/crates/fj-core/src/layers/validation.rs
@@ -31,13 +31,28 @@ impl Layer<Validation> {
 impl State for Validation {
     type Command = ValidationCommand;
     type Event = ValidationFailed;
+}
+
+/// Command for `Layer<Validation>`
+pub enum ValidationCommand {
+    /// Validate the provided object
+    ValidateObject {
+        /// The object to validate
+        object: AnyObject<Stored>,
+    },
+}
 
-    fn decide(&self, command: Self::Command, events: &mut Vec<Self::Event>) {
+impl Command<Validation> for ValidationCommand {
+    fn decide(
+        self,
+        state: &Validation,
+        events: &mut Vec<<Validation as State>::Event>,
+    ) {
         let mut errors = Vec::new();
 
-        match command {
+        match self {
             ValidationCommand::ValidateObject { object } => {
-                object.validate_with_config(&self.config, &mut errors);
+                object.validate_with_config(&state.config, &mut errors);
 
                 for err in errors {
                     events.push(ValidationFailed {
@@ -50,17 +65,6 @@ impl State for Validation {
     }
 }
 
-/// Command for `Layer<Validation>`
-pub enum ValidationCommand {
-    /// Validate the provided object
-    ValidateObject {
-        /// The object to validate
-        object: AnyObject<Stored>,
-    },
-}
-
-impl Command<Validation> for ValidationCommand {}
-
 /// Validation of an object failed
 ///
 /// Event produced by `Layer<Validation>`.

From 39edbab8218d5424fc01fe6277927f0578246db0 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 12:01:43 +0100
Subject: [PATCH 16/27] Move `State::Event` to `Command`

---
 crates/fj-core/src/layers/layer.rs      | 16 ++++++++++------
 crates/fj-core/src/layers/objects.rs    |  5 +++--
 crates/fj-core/src/layers/validation.rs |  9 +++------
 3 files changed, 16 insertions(+), 14 deletions(-)

diff --git a/crates/fj-core/src/layers/layer.rs b/crates/fj-core/src/layers/layer.rs
index 1ffc0e94a..e91412ab6 100644
--- a/crates/fj-core/src/layers/layer.rs
+++ b/crates/fj-core/src/layers/layer.rs
@@ -30,7 +30,11 @@ impl<S: State> Layer<S> {
     ///
     /// The command is processed synchronously. When this method returns, the
     /// state has been updated.
-    pub fn process(&mut self, command: S::Command, events: &mut Vec<S::Event>) {
+    pub fn process(
+        &mut self,
+        command: S::Command,
+        events: &mut Vec<<S::Command as Command<S>>::Event>,
+    ) {
         command.decide(&self.state, events);
 
         for event in events {
@@ -72,21 +76,21 @@ pub trait State: Sized {
     ///
     /// Commands are processed by [`Command::decide`].
     type Command: Command<Self>;
+}
 
+/// A command that encodes a request to update a layer's state
+pub trait Command<S: State> {
     /// An event that encodes a change to the state
     ///
     /// Events are produced by [`Command::decide`] and processed by
     /// [`Event::evolve`].
-    type Event: Event<Self>;
-}
+    type Event: Event<S>;
 
-/// A command that encodes a request to update a layer's state
-pub trait Command<S: State> {
     /// Decide which events to produce, given the command and provided state
     ///
     /// If the command must result in changes to the state, any number of events
     /// that describe these state changes can be produced.
-    fn decide(self, state: &S, events: &mut Vec<S::Event>);
+    fn decide(self, state: &S, events: &mut Vec<Self::Event>);
 }
 
 /// An event that encodes a change to a layer's state
diff --git a/crates/fj-core/src/layers/objects.rs b/crates/fj-core/src/layers/objects.rs
index d45547645..b18c012fd 100644
--- a/crates/fj-core/src/layers/objects.rs
+++ b/crates/fj-core/src/layers/objects.rs
@@ -25,7 +25,6 @@ impl Layer<Objects> {
 
 impl State for Objects {
     type Command = ObjectsCommand;
-    type Event = InsertObject;
 }
 
 /// Command for `Layer<Objects>`
@@ -42,7 +41,9 @@ pub enum ObjectsCommand {
 }
 
 impl Command<Objects> for ObjectsCommand {
-    fn decide(self, _: &Objects, events: &mut Vec<<Objects as State>::Event>) {
+    type Event = InsertObject;
+
+    fn decide(self, _: &Objects, events: &mut Vec<Self::Event>) {
         let ObjectsCommand::InsertObject { object } = self;
         events.push(InsertObject { object });
     }
diff --git a/crates/fj-core/src/layers/validation.rs b/crates/fj-core/src/layers/validation.rs
index 618fd1b07..52ee9f62d 100644
--- a/crates/fj-core/src/layers/validation.rs
+++ b/crates/fj-core/src/layers/validation.rs
@@ -30,7 +30,6 @@ impl Layer<Validation> {
 
 impl State for Validation {
     type Command = ValidationCommand;
-    type Event = ValidationFailed;
 }
 
 /// Command for `Layer<Validation>`
@@ -43,11 +42,9 @@ pub enum ValidationCommand {
 }
 
 impl Command<Validation> for ValidationCommand {
-    fn decide(
-        self,
-        state: &Validation,
-        events: &mut Vec<<Validation as State>::Event>,
-    ) {
+    type Event = ValidationFailed;
+
+    fn decide(self, state: &Validation, events: &mut Vec<Self::Event>) {
         let mut errors = Vec::new();
 
         match self {

From 2400b666810d6087f94335e0e7097e913db09012 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 12:03:10 +0100
Subject: [PATCH 17/27] Refactor to simplify

---
 crates/fj-core/src/layers/layer.rs | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/crates/fj-core/src/layers/layer.rs b/crates/fj-core/src/layers/layer.rs
index e91412ab6..f6fed4077 100644
--- a/crates/fj-core/src/layers/layer.rs
+++ b/crates/fj-core/src/layers/layer.rs
@@ -30,11 +30,10 @@ impl<S: State> Layer<S> {
     ///
     /// The command is processed synchronously. When this method returns, the
     /// state has been updated.
-    pub fn process(
-        &mut self,
-        command: S::Command,
-        events: &mut Vec<<S::Command as Command<S>>::Event>,
-    ) {
+    pub fn process<C>(&mut self, command: C, events: &mut Vec<C::Event>)
+    where
+        C: Command<S>,
+    {
         command.decide(&self.state, events);
 
         for event in events {

From 8cd1caa4c89162addb12e765f80a9b7ec38d7440 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 12:03:20 +0100
Subject: [PATCH 18/27] Remove redundant associated type

---
 crates/fj-core/src/layers/layer.rs      | 7 +------
 crates/fj-core/src/layers/objects.rs    | 4 +---
 crates/fj-core/src/layers/validation.rs | 4 +---
 3 files changed, 3 insertions(+), 12 deletions(-)

diff --git a/crates/fj-core/src/layers/layer.rs b/crates/fj-core/src/layers/layer.rs
index f6fed4077..a0dc348e9 100644
--- a/crates/fj-core/src/layers/layer.rs
+++ b/crates/fj-core/src/layers/layer.rs
@@ -70,12 +70,7 @@ where
 /// the consumer of this trait's API.
 ///
 /// See [`Layer`] for a more detailed explanation.
-pub trait State: Sized {
-    /// A command that encodes a request to update the state
-    ///
-    /// Commands are processed by [`Command::decide`].
-    type Command: Command<Self>;
-}
+pub trait State: Sized {}
 
 /// A command that encodes a request to update a layer's state
 pub trait Command<S: State> {
diff --git a/crates/fj-core/src/layers/objects.rs b/crates/fj-core/src/layers/objects.rs
index b18c012fd..d18c863ff 100644
--- a/crates/fj-core/src/layers/objects.rs
+++ b/crates/fj-core/src/layers/objects.rs
@@ -23,9 +23,7 @@ impl Layer<Objects> {
     }
 }
 
-impl State for Objects {
-    type Command = ObjectsCommand;
-}
+impl State for Objects {}
 
 /// Command for `Layer<Objects>`
 #[derive(Debug)]
diff --git a/crates/fj-core/src/layers/validation.rs b/crates/fj-core/src/layers/validation.rs
index 52ee9f62d..70649f029 100644
--- a/crates/fj-core/src/layers/validation.rs
+++ b/crates/fj-core/src/layers/validation.rs
@@ -28,9 +28,7 @@ impl Layer<Validation> {
     }
 }
 
-impl State for Validation {
-    type Command = ValidationCommand;
-}
+impl State for Validation {}
 
 /// Command for `Layer<Validation>`
 pub enum ValidationCommand {

From 8bd5e990deb549373b7297c7d744aff21bb01d5f Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 12:04:36 +0100
Subject: [PATCH 19/27] Remove redundant trait bound

---
 crates/fj-core/src/layers/layer.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/crates/fj-core/src/layers/layer.rs b/crates/fj-core/src/layers/layer.rs
index a0dc348e9..d905e4e00 100644
--- a/crates/fj-core/src/layers/layer.rs
+++ b/crates/fj-core/src/layers/layer.rs
@@ -73,7 +73,7 @@ where
 pub trait State: Sized {}
 
 /// A command that encodes a request to update a layer's state
-pub trait Command<S: State> {
+pub trait Command<S> {
     /// An event that encodes a change to the state
     ///
     /// Events are produced by [`Command::decide`] and processed by

From e38716a022309dce6e5f1b9f4dab079fe2c57a52 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 12:04:48 +0100
Subject: [PATCH 20/27] Remove redundant trait bounds

---
 crates/fj-core/src/layers/layer.rs | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/crates/fj-core/src/layers/layer.rs b/crates/fj-core/src/layers/layer.rs
index d905e4e00..7e55fd658 100644
--- a/crates/fj-core/src/layers/layer.rs
+++ b/crates/fj-core/src/layers/layer.rs
@@ -16,11 +16,11 @@ use std::ops::Deref;
 /// This design takes inspiration from, and uses the nomenclature of, this
 /// article:
 /// <https://thinkbeforecoding.com/post/2021/12/17/functional-event-sourcing-decider>
-pub struct Layer<S: State> {
+pub struct Layer<S> {
     state: S,
 }
 
-impl<S: State> Layer<S> {
+impl<S> Layer<S> {
     /// Create an instance of `Layer`
     pub fn new(state: S) -> Self {
         Self { state }
@@ -47,7 +47,7 @@ impl<S: State> Layer<S> {
     }
 }
 
-impl<S: State> Deref for Layer<S> {
+impl<S> Deref for Layer<S> {
     type Target = S;
 
     fn deref(&self) -> &Self::Target {
@@ -55,7 +55,7 @@ impl<S: State> Deref for Layer<S> {
     }
 }
 
-impl<S: State> Default for Layer<S>
+impl<S> Default for Layer<S>
 where
     S: Default,
 {

From dd499594e08043749eafbf910128dc8842a41e1e Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 12:05:07 +0100
Subject: [PATCH 21/27] Remove redundant trait

---
 crates/fj-core/src/layers/layer.rs      | 11 -----------
 crates/fj-core/src/layers/mod.rs        |  2 +-
 crates/fj-core/src/layers/objects.rs    |  4 +---
 crates/fj-core/src/layers/validation.rs |  4 +---
 4 files changed, 3 insertions(+), 18 deletions(-)

diff --git a/crates/fj-core/src/layers/layer.rs b/crates/fj-core/src/layers/layer.rs
index 7e55fd658..edbdcc48b 100644
--- a/crates/fj-core/src/layers/layer.rs
+++ b/crates/fj-core/src/layers/layer.rs
@@ -10,9 +10,6 @@ use std::ops::Deref;
 /// processed by [`Layer::process`]. Processing a command can result in any
 /// number of events, which can then be used as commands for other layers.
 ///
-/// All of this is mediated through [`State`], which the wrapped state must
-/// implement.
-///
 /// This design takes inspiration from, and uses the nomenclature of, this
 /// article:
 /// <https://thinkbeforecoding.com/post/2021/12/17/functional-event-sourcing-decider>
@@ -64,14 +61,6 @@ where
     }
 }
 
-/// The state of a specific layer
-///
-/// Implementations of this trait are wrapped by the generic [`Layer`], which is
-/// the consumer of this trait's API.
-///
-/// See [`Layer`] for a more detailed explanation.
-pub trait State: Sized {}
-
 /// A command that encodes a request to update a layer's state
 pub trait Command<S> {
     /// An event that encodes a change to the state
diff --git a/crates/fj-core/src/layers/mod.rs b/crates/fj-core/src/layers/mod.rs
index d077897fa..d18457b73 100644
--- a/crates/fj-core/src/layers/mod.rs
+++ b/crates/fj-core/src/layers/mod.rs
@@ -9,6 +9,6 @@ mod layer;
 mod layers;
 
 pub use self::{
-    layer::{Command, Event, Layer, State},
+    layer::{Command, Event, Layer},
     layers::Layers,
 };
diff --git a/crates/fj-core/src/layers/objects.rs b/crates/fj-core/src/layers/objects.rs
index d18c863ff..3319eac02 100644
--- a/crates/fj-core/src/layers/objects.rs
+++ b/crates/fj-core/src/layers/objects.rs
@@ -5,7 +5,7 @@ use crate::{
     validate::Validation,
 };
 
-use super::{Command, Event, Layer, State};
+use super::{Command, Event, Layer};
 
 impl Layer<Objects> {
     /// Insert and object into the stores
@@ -23,8 +23,6 @@ impl Layer<Objects> {
     }
 }
 
-impl State for Objects {}
-
 /// Command for `Layer<Objects>`
 #[derive(Debug)]
 pub enum ObjectsCommand {
diff --git a/crates/fj-core/src/layers/validation.rs b/crates/fj-core/src/layers/validation.rs
index 70649f029..7f670d5b8 100644
--- a/crates/fj-core/src/layers/validation.rs
+++ b/crates/fj-core/src/layers/validation.rs
@@ -5,7 +5,7 @@ use crate::{
     validate::{Validation, ValidationError, ValidationErrors},
 };
 
-use super::{objects::InsertObject, Command, Event, Layer, State};
+use super::{objects::InsertObject, Command, Event, Layer};
 
 impl Layer<Validation> {
     /// Handler for [`InsertObject`]
@@ -28,8 +28,6 @@ impl Layer<Validation> {
     }
 }
 
-impl State for Validation {}
-
 /// Command for `Layer<Validation>`
 pub enum ValidationCommand {
     /// Validate the provided object

From 3e3c49eafaa473baa40e135969866b1559c755cc Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 12:13:40 +0100
Subject: [PATCH 22/27] Refactor to simplify

---
 crates/fj-core/src/layers/validation.rs | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/crates/fj-core/src/layers/validation.rs b/crates/fj-core/src/layers/validation.rs
index 7f670d5b8..6b1572571 100644
--- a/crates/fj-core/src/layers/validation.rs
+++ b/crates/fj-core/src/layers/validation.rs
@@ -43,17 +43,15 @@ impl Command<Validation> for ValidationCommand {
     fn decide(self, state: &Validation, events: &mut Vec<Self::Event>) {
         let mut errors = Vec::new();
 
-        match self {
-            ValidationCommand::ValidateObject { object } => {
-                object.validate_with_config(&state.config, &mut errors);
+        let ValidationCommand::ValidateObject { object } = self;
 
-                for err in errors {
-                    events.push(ValidationFailed {
-                        object: object.clone(),
-                        err,
-                    });
-                }
-            }
+        object.validate_with_config(&state.config, &mut errors);
+
+        for err in errors {
+            events.push(ValidationFailed {
+                object: object.clone(),
+                err,
+            });
         }
     }
 }

From 01247c3d9ab3018094817f2d05ef122b04cbb7b5 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 12:15:18 +0100
Subject: [PATCH 23/27] Remove redundant command

---
 crates/fj-core/src/layers/validation.rs | 18 +++---------------
 1 file changed, 3 insertions(+), 15 deletions(-)

diff --git a/crates/fj-core/src/layers/validation.rs b/crates/fj-core/src/layers/validation.rs
index 6b1572571..0f34f5002 100644
--- a/crates/fj-core/src/layers/validation.rs
+++ b/crates/fj-core/src/layers/validation.rs
@@ -10,9 +10,7 @@ use super::{objects::InsertObject, Command, Event, Layer};
 impl Layer<Validation> {
     /// Handler for [`InsertObject`]
     pub fn on_insert_object(&mut self, event: InsertObject) {
-        let command = ValidationCommand::ValidateObject {
-            object: event.object.into(),
-        };
+        let command = event;
         self.process(command, &mut Vec::new());
     }
 
@@ -28,23 +26,13 @@ impl Layer<Validation> {
     }
 }
 
-/// Command for `Layer<Validation>`
-pub enum ValidationCommand {
-    /// Validate the provided object
-    ValidateObject {
-        /// The object to validate
-        object: AnyObject<Stored>,
-    },
-}
-
-impl Command<Validation> for ValidationCommand {
+impl Command<Validation> for InsertObject {
     type Event = ValidationFailed;
 
     fn decide(self, state: &Validation, events: &mut Vec<Self::Event>) {
         let mut errors = Vec::new();
 
-        let ValidationCommand::ValidateObject { object } = self;
-
+        let object: AnyObject<Stored> = self.object.into();
         object.validate_with_config(&state.config, &mut errors);
 
         for err in errors {

From bf633a60ac463a609a885f3f3b10d6edd45e4629 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 12:15:31 +0100
Subject: [PATCH 24/27] Inline redundant variable

---
 crates/fj-core/src/layers/validation.rs | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/crates/fj-core/src/layers/validation.rs b/crates/fj-core/src/layers/validation.rs
index 0f34f5002..877ef6644 100644
--- a/crates/fj-core/src/layers/validation.rs
+++ b/crates/fj-core/src/layers/validation.rs
@@ -10,8 +10,7 @@ use super::{objects::InsertObject, Command, Event, Layer};
 impl Layer<Validation> {
     /// Handler for [`InsertObject`]
     pub fn on_insert_object(&mut self, event: InsertObject) {
-        let command = event;
-        self.process(command, &mut Vec::new());
+        self.process(event, &mut Vec::new());
     }
 
     /// Consume the validation layer, returning any validation errors

From 0e5ab8dcb3ff753a57e479fc89056288b511d231 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 12:16:11 +0100
Subject: [PATCH 25/27] Inline redundant method

---
 crates/fj-core/src/layers/objects.rs    | 2 +-
 crates/fj-core/src/layers/validation.rs | 5 -----
 2 files changed, 1 insertion(+), 6 deletions(-)

diff --git a/crates/fj-core/src/layers/objects.rs b/crates/fj-core/src/layers/objects.rs
index 3319eac02..d4e6badc0 100644
--- a/crates/fj-core/src/layers/objects.rs
+++ b/crates/fj-core/src/layers/objects.rs
@@ -18,7 +18,7 @@ impl Layer<Objects> {
         self.process(ObjectsCommand::InsertObject { object }, &mut events);
 
         for event in events {
-            validation.on_insert_object(event);
+            validation.process(event, &mut Vec::new());
         }
     }
 }
diff --git a/crates/fj-core/src/layers/validation.rs b/crates/fj-core/src/layers/validation.rs
index 877ef6644..96071ee9e 100644
--- a/crates/fj-core/src/layers/validation.rs
+++ b/crates/fj-core/src/layers/validation.rs
@@ -8,11 +8,6 @@ use crate::{
 use super::{objects::InsertObject, Command, Event, Layer};
 
 impl Layer<Validation> {
-    /// Handler for [`InsertObject`]
-    pub fn on_insert_object(&mut self, event: InsertObject) {
-        self.process(event, &mut Vec::new());
-    }
-
     /// Consume the validation layer, returning any validation errors
     pub fn into_result(self) -> Result<(), ValidationErrors> {
         let errors = self.into_state().into_errors();

From 421bdb96a738b5e496babd7271493092848a4281 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 12:18:09 +0100
Subject: [PATCH 26/27] Remove redundant command

---
 crates/fj-core/src/layers/objects.rs | 32 ++++++++--------------------
 1 file changed, 9 insertions(+), 23 deletions(-)

diff --git a/crates/fj-core/src/layers/objects.rs b/crates/fj-core/src/layers/objects.rs
index d4e6badc0..121d60dc2 100644
--- a/crates/fj-core/src/layers/objects.rs
+++ b/crates/fj-core/src/layers/objects.rs
@@ -15,7 +15,7 @@ impl Layer<Objects> {
         validation: &mut Layer<Validation>,
     ) {
         let mut events = Vec::new();
-        self.process(ObjectsCommand::InsertObject { object }, &mut events);
+        self.process(InsertObject { object }, &mut events);
 
         for event in events {
             validation.process(event, &mut Vec::new());
@@ -23,28 +23,6 @@ impl Layer<Objects> {
     }
 }
 
-/// Command for `Layer<Objects>`
-#[derive(Debug)]
-pub enum ObjectsCommand {
-    /// Insert an object into the stores
-    ///
-    /// This is the one primitive operation that all other operations are built
-    /// upon.
-    InsertObject {
-        /// The object to insert
-        object: AnyObject<AboutToBeStored>,
-    },
-}
-
-impl Command<Objects> for ObjectsCommand {
-    type Event = InsertObject;
-
-    fn decide(self, _: &Objects, events: &mut Vec<Self::Event>) {
-        let ObjectsCommand::InsertObject { object } = self;
-        events.push(InsertObject { object });
-    }
-}
-
 /// Insert an object into the stores
 ///
 /// Event produced by `Layer<Objects>`.
@@ -54,6 +32,14 @@ pub struct InsertObject {
     pub object: AnyObject<AboutToBeStored>,
 }
 
+impl Command<Objects> for InsertObject {
+    type Event = InsertObject;
+
+    fn decide(self, _: &Objects, events: &mut Vec<Self::Event>) {
+        events.push(self);
+    }
+}
+
 impl Event<Objects> for InsertObject {
     fn evolve(&self, state: &mut Objects) {
         self.object.clone().insert(state);

From b4e6e0717ddea6016cdbf3745b80d31b3020d468 Mon Sep 17 00:00:00 2001
From: Hanno Braun <hanno@braun-odw.eu>
Date: Thu, 15 Feb 2024 12:17:08 +0100
Subject: [PATCH 27/27] Update documentation of `layers`

---
 crates/fj-core/src/layers/layer.rs   | 4 ++--
 crates/fj-core/src/layers/layers.rs  | 2 +-
 crates/fj-core/src/layers/objects.rs | 7 +++++--
 3 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/crates/fj-core/src/layers/layer.rs b/crates/fj-core/src/layers/layer.rs
index edbdcc48b..4f4148a9a 100644
--- a/crates/fj-core/src/layers/layer.rs
+++ b/crates/fj-core/src/layers/layer.rs
@@ -80,8 +80,8 @@ pub trait Command<S> {
 pub trait Event<S> {
     /// Evolve the provided state
     ///
-    /// This is the only method that gets mutable access to the state, making
-    /// sure that all changes to the state are captured as events.
+    /// This is the only method that [`Layer`] gives mutable access to the
+    /// state, making sure that all changes to the state are captured as events.
     ///
     /// Implementations of this method are supposed to be relatively dumb. Any
     /// decisions that go into updating the state should be made in
diff --git a/crates/fj-core/src/layers/layers.rs b/crates/fj-core/src/layers/layers.rs
index 2682537a8..200fd4529 100644
--- a/crates/fj-core/src/layers/layers.rs
+++ b/crates/fj-core/src/layers/layers.rs
@@ -21,7 +21,7 @@ use super::Layer;
 /// That can be changed, once necessary.
 #[derive(Default)]
 pub struct Layers {
-    /// The objects layers
+    /// The objects layer
     ///
     /// Manages the stores of topological and geometric objects that make up
     /// shapes.
diff --git a/crates/fj-core/src/layers/objects.rs b/crates/fj-core/src/layers/objects.rs
index 121d60dc2..b5cff0ea2 100644
--- a/crates/fj-core/src/layers/objects.rs
+++ b/crates/fj-core/src/layers/objects.rs
@@ -8,7 +8,9 @@ use crate::{
 use super::{Command, Event, Layer};
 
 impl Layer<Objects> {
-    /// Insert and object into the stores
+    /// Insert an object into the stores
+    ///
+    /// Passes any events produced to the validation layer.
     pub fn insert(
         &mut self,
         object: AnyObject<AboutToBeStored>,
@@ -25,7 +27,8 @@ impl Layer<Objects> {
 
 /// Insert an object into the stores
 ///
-/// Event produced by `Layer<Objects>`.
+/// This struct serves as both event and command for `Layer<Objects>`, as well
+/// as a command for `Layer<Validation>`.
 #[derive(Clone, Debug)]
 pub struct InsertObject {
     /// The object to insert