Communicate with exceptions

Co-authored-by: Szymon Fiedler <[email protected]>
Co-authored-by: Piotr Jurewicz <[email protected]>

examples/decider/lib/project_management/command_handler.rb

@@ -17,16 +17,13 @@ def handle(cmd)
           version = idx
         end
 
-      case result = decider.decide(cmd)
-      when StandardError
-        raise Error
-      else
-        @event_store.publish(
-          result,
-          stream_name: stream_name(cmd.id),
-          expected_version: version
-        )
-      end
+      @event_store.publish(
+        decider.decide(cmd),
+        stream_name: stream_name(cmd.id),
+        expected_version: version
+      )
+    rescue Issue::InvalidTransition
+      raise Error
     end
 
     private

examples/decider/lib/project_management/issue.rb

@@ -1,6 +1,7 @@
 module ProjectManagement
   class Issue
     InvalidTransition = Class.new(StandardError)
+
     State = Data.define(:id, :status)
     private_constant :State
 
@@ -46,53 +47,37 @@ def evolve(event)
     private
 
     def open
-      if @state.status
-        InvalidTransition.new
-      else
-        IssueOpened.new(data: { issue_id: @state.id })
-      end
+      fail if @state.status
+      IssueOpened.new(data: { issue_id: @state.id })
     end
 
     def resolve
-      if %i[open in_progress reopened].include? @state.status
-        IssueResolved.new(data: { issue_id: @state.id })
-      else
-        InvalidTransition.new
-      end
+      fail unless %i[open in_progress reopened].include? @state.status
+      IssueResolved.new(data: { issue_id: @state.id })
     end
 
     def close
-      if %i[open in_progress resolved reopened].include? @state.status
-        IssueClosed.new(data: { issue_id: @state.id })
-      else
-        InvalidTransition.new
-      end
+      fail unless %i[open in_progress resolved reopened].include? @state.status
+      IssueClosed.new(data: { issue_id: @state.id })
     end
 
     def reopen
-      if %i[resolved closed].include? @state.status
-        IssueReopened.new(data: { issue_id: @state.id })
-      else
-        InvalidTransition.new
-      end
+      fail unless %i[resolved closed].include? @state.status
+      IssueReopened.new(data: { issue_id: @state.id })
     end
 
-    def stop
-      if %i[in_progress].include? @state.status
-        IssueProgressStopped.new(data: { issue_id: @state.id })
-      else
-        InvalidTransition.new
-      end
+    def start
+      fail unless %i[open reopened].include? @state.status
+      IssueProgressStarted.new(data: { issue_id: @state.id })
     end
 
-    def start
-      if %i[open reopened].include? @state.status
-        IssueProgressStarted.new(data: { issue_id: @state.id })
-      else
-        InvalidTransition.new
-      end
+    def stop
+      fail unless %i[in_progress].include? @state.status
+      IssueProgressStopped.new(data: { issue_id: @state.id })
     end
 
+    def fail = raise InvalidTransition
+
     def initial_state(id) = State.new(id: id, status: nil)
   end
 end