Use a guard and provide a fatal error with message

alexjameslittle · web-flow · commit c75e00fd515b · 2020-02-09T17:00:39.000Z
diff --git a/Sources/CombineDataSources/CollectionView/CollectionViewItemsController.swift b/Sources/CombineDataSources/CollectionView/CollectionViewItemsController.swift
@@ -102,7 +102,10 @@ public class CollectionViewItemsController<CollectionType>: NSObject, UICollecti
   }
 
   public func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
-      return configureSupplementaryView!(self, collectionView, kind, indexPath, collection[indexPath.section])
+      guard let configureSupplementaryView = configureSupplementaryView else {
+        fatalError("Property `configureSupplementaryView` must not be nil when using supplementary views")
+      }
+      return configureSupplementaryView(self, collectionView, kind, indexPath, collection[indexPath.section])
   }
   
   // MARK: - Fallback data source object

Original file line number	Diff line number	Diff line change
`@@ -102,7 +102,10 @@ public class CollectionViewItemsController<CollectionType>: NSObject, UICollecti`
`102`	`102`	`}`
`103`	`103`
`104`	`104`	`public func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {`
`105`		`- return configureSupplementaryView!(self, collectionView, kind, indexPath, collection[indexPath.section])`
	`105`	`+ guard let configureSupplementaryView = configureSupplementaryView else {`
	`106`	+ fatalError("Property `configureSupplementaryView` must not be nil when using supplementary views")
	`107`	`+ }`
	`108`	`+ return configureSupplementaryView(self, collectionView, kind, indexPath, collection[indexPath.section])`
`106`	`109`	`}`
`107`	`110`
`108`	`111`	`// MARK: - Fallback data source object`