Add EnumeratorBuilder abstraction

app/jobs/maintenance_tasks/task_job.rb

@@ -28,7 +28,7 @@ def retry_on(*, **)
     def build_enumerator(_run, cursor:)
       context = Task::EnumerationContext.new(cursor: cursor || @run.cursor)
 
-      @task.enumerator(context: context)
+      @task.enumerator_builder.enumerator(context: context)
     end
 
     # Performs task iteration logic for the current input returned by the

app/tasks/maintenance_tasks/active_record_task.rb

@@ -7,11 +7,17 @@ class ActiveRecordTask < Task
 
     # TODO: specify abstract_class
 
+    EnumeratorBuilder = Struct.new(:collection) do
+      def enumerator(context:)
+        enumerator_builder.active_record_on_records(collection, cursor: context.cursor)
+      end
+    end
+
     def enumerator(context:)
       collection = self.collection
       assert_relation!(collection)
 
-      enumerator_builder.active_record_on_records(collection, cursor: context.cursor)
+      EnumeratorBuilder.new(collection)
     end
 
     def collection

app/tasks/maintenance_tasks/array_task.rb

@@ -7,11 +7,17 @@ class ActiveRecordTask < Task
 
     # TODO: Specify abstract_class
 
+    EnumeratorBuilder = Struct.new(:collection) do
+      def enumerator(context:)
+        enumerator_builder.array(collection, cursor: context.cursor)
+      end
+    end
+
     def enumerator(context:)
       collection = self.collection
       assert_array!(collection)
 
-      enumerator_builder.array(collection, cursor: context.cursor)
+      EnumeratorBuilder.new(collection)
     end
 
     def collection

app/tasks/maintenance_tasks/csv_task.rb

@@ -8,13 +8,19 @@ module MaintenanceTasks
   class CsvTask < Task
     # TODO: specify abstract_class
 
+    EnumeratorBuilder = Struct.new(:collection) do
+      def enumerator(context:)
+        JobIteration::CsvEnumerator.new(collection).rows(cursor: context.cursor)
+      end
+    end
+
     # The contents of a CSV file to be processed by a Task.
     #
     # @return [String] the content of the CSV file to process.
     attr_accessor :csv_content
 
-    def enumerator(context:)
-      JobIteration::CsvEnumerator.new(collection).rows(cursor: context.cursor)
+    def enumerator_builder(context:)
+      EnumeratorBuilder.new(collection)
     end
 
     # The number of rows to be processed. Excludes the header row from the count

app/tasks/maintenance_tasks/task.rb

@@ -79,9 +79,9 @@ def load_constants
     #
     # @raise [NotImplementedError] with a message advising subclasses to
     #   implement an override for this method.
-    def enumerator(context:)
+    def enumerator_builder(context:)
       raise NotImplementedError,
-        "#{self.class.name} must implement `enumerator` or inherit from a class which does"
+        "#{self.class.name} must implement `#{__method__}` or inherit from a class which does"
       # TODO: Could make error string list available adapters
     end
 

example.rb

@@ -25,22 +25,28 @@ def process(row) BetaFlag[:whatever].enable(row.shop_id) end
 end
 
 class PaymentTask < MaintenanceTasks::Task
-  # Consumers implement .enumerator instead of .collection, without having to
-  # know that other tasks actually also use .enumerator internally
-  def enumerator(context:)
-    Enumerator.new do |yielder|
-      cursor = context.cursor
-      loop do
-        page = cursor ? InvoiceAPI.fetch(after: cursor) : InvoiceAPI.fetch_all
-        break if page.empty?
-        page.each do |invoice|
-          cursor = invoice.id
-          yielder.yield(invoice, cursor)
+  # Consumers implement .build_enumerator instead of .collection, without
+  # having to know that other tasks actually also use it internally
+  class EnumeratorBuilder
+    def enumerator(context:)
+      Enumerator.new do |yielder|
+        cursor = context.cursor
+        loop do
+          page = cursor ? InvoiceAPI.fetch(after: cursor) : InvoiceAPI.fetch_all
+          break if page.empty?
+          page.each do |invoice|
+            cursor = invoice.id
+            yielder.yield(invoice, cursor)
+          end
         end
       end
     end
   end
 
+  def build_enumerator
+    Enumerator.new
+  end
+
   # Again, can be implemented if appropriate
   def count() InvoiceAPI.unpaid_count end