Alternative: Register mapper function of options instead of just the extra options

The solution described in comment coinbase#423 (comment). It mostly demonstrates that it adds too much complexity for what it gains.

Author: bisgardo

statefulsyncer/configuration.go

@@ -69,8 +69,8 @@ func WithSeenConcurrency(concurrency int64) Option {
 	}
 }
 
-func WithExtraSyncerOpts(os ...syncer.Option) Option {
+func WithCustomSyncerOpts(mapper func(...syncer.Option) []syncer.Option) Option {
 	return func(s *StatefulSyncer) {
-		s.extraSyncerOpts = os
+		s.mapSyncerOpts = mapper
 	}
 }

statefulsyncer/stateful_syncer.go

@@ -73,7 +73,7 @@ type StatefulSyncer struct {
 	seenSemaphore     *semaphore.Weighted
 	seenSemaphoreSize int64
 
-	extraSyncerOpts []syncer.Option
+	mapSyncerOpts func(...syncer.Option) []syncer.Option
 }
 
 // Logger is used by the statefulsyncer to
@@ -164,12 +164,12 @@ func (s *StatefulSyncer) Sync(ctx context.Context, startIndex int64, endIndex in
 		s,
 		s,
 		s.cancel,
-		append([]syncer.Option{
+		s.mapSyncerOpts(
 			syncer.WithPastBlocks(pastBlocks),
 			syncer.WithCacheSize(s.cacheSize),
 			syncer.WithMaxConcurrency(s.maxConcurrency),
 			syncer.WithAdjustmentWindow(s.adjustmentWindow),
-		}, s.extraSyncerOpts...)...,
+		)...,
 	)
 
 	return syncer.Sync(ctx, startIndex, endIndex)