Improve devex ergonomics for impl Command

Author: jwilger

src/command.rs

@@ -3,11 +3,12 @@ use crate::event::Event;
 use crate::event_store::EventStreamId;
 use std::fmt::Debug;
 
-pub trait Command<E: Event>: Clone {
-    type State: AggregateState<E>;
+pub trait Command: Clone {
+    type Event: Event;
+    type State: AggregateState<Self::Event>;
     type Error: std::error::Error + Send + Sync + 'static;
 
-    fn handle(&self) -> Result<Vec<E>, Self::Error>;
+    fn handle(&self) -> Result<Vec<Self::Event>, Self::Error>;
 
     fn event_stream_id(&self) -> EventStreamId;
 
@@ -26,29 +27,14 @@ pub trait Command<E: Event>: Clone {
         None
     }
 
-    fn apply(&mut self, event: &E)
+    fn apply(&mut self, event: &Self::Event)
     where
         Self: Sized,
     {
         self.set_state(self.get_state().apply(event));
     }
 }
 
-impl<E: Event> Command<E> for () {
-    type State = ();
-    type Error = std::convert::Infallible;
-
-    fn handle(&self) -> Result<Vec<E>, Self::Error> {
-        Ok(vec![])
-    }
-    fn event_stream_id(&self) -> EventStreamId {
-        EventStreamId::new()
-    }
-    fn get_state(&self) -> Self::State {}
-    fn set_state(&mut self, _: Self::State) {}
-    fn mark_retry(&self) -> Self {}
-}
-
 pub trait AggregateState<E: Event>: Debug + Sized {
     fn apply(&self, event: &E) -> Self;
 }

src/lib.rs

@@ -20,7 +20,7 @@ pub async fn execute<E, C, S>(
 ) -> Result<(), Error>
 where
     E: Event,
-    C: Command<E>,
+    C: Command<Event = E>,
     S: EventStore,
 {
     let mut retries = 0;
@@ -168,7 +168,8 @@ mod tests {
         }
     }
 
-    impl Command<TestEvent> for AlwaysConflictingCommand {
+    impl Command for AlwaysConflictingCommand {
+        type Event = TestEvent;
         type State = ();
         type Error = Error;
 
@@ -324,7 +325,8 @@ mod tests {
         state: StatefulCommandState,
     }
 
-    impl Command<TestEvent> for ConcurrentModificationCommand {
+    impl Command for ConcurrentModificationCommand {
+        type Event = TestEvent;
         type State = StatefulCommandState;
         type Error = Error;
 
@@ -459,7 +461,8 @@ mod tests {
         id: Uuid,
     }
 
-    impl Command<TestEvent> for EventProducingCommand {
+    impl Command for EventProducingCommand {
+        type Event = TestEvent;
         type State = ();
         type Error = Infallible;
 

tests/test_cases.rs

@@ -21,7 +21,8 @@ impl NoopCommand {
     }
 }
 
-impl Command<()> for NoopCommand {
+impl Command for NoopCommand {
+    type Event = ();
     type State = ();
     type Error = Infallible;
 
@@ -50,7 +51,8 @@ impl RejectCommand {
     }
 }
 
-impl Command<()> for RejectCommand {
+impl Command for RejectCommand {
+    type Event = ();
     type State = ();
     type Error = RejectCommandError;
 
@@ -75,7 +77,8 @@ impl EventProducingCommand {
     }
 }
 
-impl Command<TestEvent> for EventProducingCommand {
+impl Command for EventProducingCommand {
+    type Event = TestEvent;
     type State = ();
     type Error = Infallible;
 
@@ -132,7 +135,8 @@ impl StatefulCommand {
     }
 }
 
-impl Command<TestEvent> for StatefulCommand {
+impl Command for StatefulCommand {
+    type Event = TestEvent;
     type State = StatefulCommandState;
     type Error = Infallible;