Add Disable() method to configurers.

aggregate.go

@@ -94,6 +94,17 @@ type AggregateConfigurer interface {
 	// Aggregate handlers support the HandlesCommand() and RecordsEvent() route
 	// types.
 	Routes(...AggregateRoute)
+
+	// Disable prevents the handler from receiving any messages.
+	//
+	// The engine MUST NOT call any methods other than Configure() on a disabled
+	// handler.
+	//
+	// Disabling a handler is useful when the handler's configuration prevents
+	// it from operating, such as when it's missing a required dependency,
+	// without requiring the user to conditionally register the handler with the
+	// application.
+	Disable(...DisableOption)
 }
 
 // AggregateCommandScope performs engine operations within the context of a call

disable.go

@@ -0,0 +1,4 @@
+package dogma
+
+// DisableOption is an option that affects the behavior of a disabled handler.
+type DisableOption struct{}

integration.go

@@ -56,6 +56,17 @@ type IntegrationConfigurer interface {
 	// Integration handlers support the HandlesCommand() and RecordsEvent()
 	// route types.
 	Routes(...IntegrationRoute)
+
+	// Disable prevents the handler from receiving any messages.
+	//
+	// The engine MUST NOT call any methods other than Configure() on a disabled
+	// handler.
+	//
+	// Disabling a handler is useful when the handler's configuration prevents
+	// it from operating, such as when it's missing a required dependency,
+	// without requiring the user to conditionally register the handler with the
+	// application.
+	Disable(...DisableOption)
 }
 
 // IntegrationCommandScope performs engine operations within the context of a

process.go

@@ -119,6 +119,17 @@ type ProcessConfigurer interface {
 	// Process handlers support the HandlesEvent(), ExecutesCommand() and
 	// SchedulesTimeout() route types.
 	Routes(...ProcessRoute)
+
+	// Disable prevents the handler from receiving any messages.
+	//
+	// The engine MUST NOT call any methods other than Configure() on a disabled
+	// handler.
+	//
+	// Disabling a handler is useful when the handler's configuration prevents
+	// it from operating, such as when it's missing a required dependency,
+	// without requiring the user to conditionally register the handler with the
+	// application.
+	Disable(...DisableOption)
 }
 
 // ProcessEventScope performs engine operations within the context of a call

projection.go

@@ -114,6 +114,17 @@ type ProjectionConfigurer interface {
 	//
 	// The default policy is UnicastProjectionDeliveryPolicy.
 	DeliveryPolicy(ProjectionDeliveryPolicy)
+
+	// Disable prevents the handler from receiving any messages.
+	//
+	// The engine MUST NOT call any methods other than Configure() on a disabled
+	// handler.
+	//
+	// Disabling a handler is useful when the handler's configuration prevents
+	// it from operating, such as when it's missing a required dependency,
+	// without requiring the user to conditionally register the handler with the
+	// application.
+	Disable(...DisableOption)
 }
 
 // ProjectionEventScope performs engine operations within the context of a call