SparseSet iterator implementation

Sources/FirebladeECS/SparseSet.swift

@@ -65,15 +65,31 @@ public class SparseSet<Element>: UniformStorage, Sequence {
 		sparse.removeAll(keepingCapacity: keepingCapacity)
 	}
 
-	public func makeIterator() -> AnyIterator<Element> {
+	public func makeIterator() -> SparseIterator<Element> {
+		return SparseIterator<Element>(self)
+		/*
+		// NOTE: was optimized by using a dedicated iterator implementation
 		var iter = dense.makeIterator()
-		return AnyIterator<Element> {
-			guard let next: Pair? = iter.next() else { return nil }
-			guard let pair: Pair = next else { return nil }
-			return pair.value
-		}
+		return AnyIterator<Element>.init {
+		guard let next: Pair = iter.next() as? Pair else { return nil }
+		return next.value
+		}*/
 	}
 
+	public struct SparseIterator<Element>: IteratorProtocol {
+		private let sparseSet: SparseSet<Element>
+		private var iterator: IndexingIterator<ContiguousArray<(key: Index, value: Element)?>>
+		init(_ sparseSet: SparseSet<Element>) {
+			self.sparseSet = sparseSet
+			self.iterator = sparseSet.dense.makeIterator()
+		}
+
+		mutating public func next() -> Element? {
+			guard let next: Pair = iterator.next() as? Pair else { return nil }
+			return next.value as? Element
+		}
+
+	}
 }
 
 public class SparseComponentSet: SparseSet<Component> {