Add clear() API, which removes all entries from the BTree

src/BTree.mo

@@ -43,6 +43,17 @@ module {
       order = btreeOrder;
     }
   };
+
+  /// Clears all entries from a BTree
+  public func clear<K, V>(tree: BTree<K, V>): () {
+    tree.root := #leaf({
+      data = {
+        kvs = Array.tabulateVar<?(K, V)>(tree.order - 1, func(i) { null });
+        var count = 0;
+      };
+    });
+    tree.size := 0;
+  };
 
   /// Allows one to quickly create a BTree from an array of key value pairs
   public func fromArray<K, V>(order: Nat, compare: (K, K) -> O.Order, kvPairs: [(K, V)]): BTree<K, V> {

test/BTreeTest.mo

@@ -93,6 +93,43 @@ let initSuite = S.suite("init", [
   */
 ]);
 
+let clearSuite = S.suite("clear", [
+  S.test("on an empty BTree, returns an empty BTree",
+    do {
+      let bt = BT.init<Nat, Nat>(?4);
+      BT.clear<Nat, Nat>(bt);
+      bt;
+    },
+    M.equals(testableNatBTree({
+      var root = #leaf({
+        data = {
+          kvs = [var null, null, null];
+          var count = 0;
+        }
+      });
+      var size = 0;
+      order = 4;
+    }))
+  ),
+  S.test("on a BTree with elements, returns an empty BTree",
+    do {
+      let bt = quickCreateBTreeWithKVPairs(4, [2, 4, 6]);
+      BT.clear<Nat, Nat>(bt);
+      bt;
+    },
+    M.equals(testableNatBTree({
+      var root = #leaf({
+        data = {
+          kvs = [var null, null, null];
+          var count = 0;
+        }
+      });
+      var size = 0;
+      order = 4;
+    }))
+  )
+]);
+
 let getSuite = S.suite("get", [
   S.test("returns null on an empty BTree",
     BT.get<Nat, Nat>(BT.init<Nat, Nat>(?4), Nat.compare, 5),
@@ -4459,6 +4496,7 @@ let maxSuite = S.suite("max", [
 S.run(S.suite("BTree",
   [
     initSuite,
+    clearSuite,
     getSuite,
     insertSuite,
     substituteKeySuite,