Add removeAll method.

HAMT/HAMT.swift

@@ -104,6 +104,12 @@ extension HAMT: Sequence {
     }
 }
 
+public extension HAMT {
+    mutating func removeAll() {
+        self = HAMT()
+    }
+}
+
 /// A zero-cost wrapper to route system hash value
 /// to `PD5Hashable` protocol.
 private struct PD5Key<K>: PD5Hashable where K: Hashable {

HAMTTests/HAMTTests.swift

@@ -0,0 +1,23 @@
+//
+//  File.swift
+//  
+//
+//  Created by Henry Hathaway on 10/4/19.
+//
+
+import Foundation
+import XCTest
+import GameKit
+@testable import HAMT
+
+final class HAMTTests: XCTestCase {
+    func testRemoveAll() {
+        var x = HAMT<Int,Int>()
+        x[111] = 222
+        x[222] = 444
+        x[333] = 666
+        XCTAssertEqual(x.count, 3)
+        x.removeAll()
+        XCTAssertEqual(x.count, 0)
+    }
+}

Package.swift

@@ -16,6 +16,7 @@ let package = Package(
     ],
     targets: [
         .target(name: "HAMT", dependencies: [], path: "HAMT"),
+        .testTarget(name: "HAMTTests", dependencies: ["HAMT"], path: "HAMTTests"),
         .testTarget(name: "PD5UnitTests", dependencies: ["HAMT"], path: "PD5UnitTests"),
         .target(name: "HAMTFuzz", dependencies: ["HAMT"], path: "HAMTFuzz"),
     ]