Extend BitmapIndexedMapNode with Sequence protocol

Further adds `count`to the node implementation for checking invariants.

Author: msteindorfer

Sources/Capsule/_BitmapIndexedMapNode.swift

@@ -26,6 +26,8 @@ final class BitmapIndexedMapNode<Key, Value>: MapNode where Key: Hashable {
         self.bitmap1 = dataMap ^ collMap
         self.bitmap2 = nodeMap ^ collMap
         self.content = content
+
+        assert(count - payloadArity >= 2 * nodeArity)
     }
 
     convenience init(dataMap: Bitmap = 0, nodeMap: Bitmap = 0, collMap: Bitmap = 0, arrayLiteral content: Any...) {
@@ -47,6 +49,10 @@ final class BitmapIndexedMapNode<Key, Value>: MapNode where Key: Hashable {
         self.init(0, 0, collMap, elements)
     }
 
+    var count: Int {
+        self.reduce(0, { count, _ in count + 1 })
+    }
+
     func get(_ key: Key, _ keyHash: Int, _ shift: Int) -> Value? {
         let mask = maskFrom(keyHash, shift)
         let bitpos = bitposFrom(mask)
@@ -521,3 +527,9 @@ extension BitmapIndexedMapNode: Equatable where Value: Equatable {
         return true
     }
 }
+
+extension BitmapIndexedMapNode: Sequence {
+    public __consuming func makeIterator() -> MapKeyValueTupleIterator<Key, Value> {
+        return MapKeyValueTupleIterator(rootNode: self)
+    }
+}