Fail if non-type based event handler is defined in projector

lib/sequent/core/projector.rb

@@ -107,6 +107,12 @@ def initialize(persistor = Sequent::Core::Persistors::ActiveRecordPersistor.new)
         @persistor = persistor
       end
 
+      def self.on(*args, **opts, &block)
+        fail ArgumentError, 'only type based event handlers are allowed for projectors' unless args.all?(Class)
+
+        super
+      end
+
       def self.replay_persistor
         nil
       end

spec/lib/sequent/core/projector_spec.rb

@@ -8,6 +8,18 @@ class MyProjectorTable
   class MyProjectorEvent < Sequent::Core::Event
   end
 
+  it 'fails when non-type based event handler is present' do
+    expect do
+      Class.new(Sequent::Core::Projector) do
+        manages_no_tables
+        self.skip_autoregister = true
+
+        on is_a(String) do
+        end
+      end
+    end.to raise_error(ArgumentError, 'only type based event handlers are allowed for projectors')
+  end
+
   it 'fails when missing managed_tables' do
     class TestProjector1 < Sequent::Core::Projector
       self.skip_autoregister = true