Bring the YAML package's style up to modern standards.

pkg/yaml/lib/src/deep_equals.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-library deep_equals;
+library yaml.deep_equals;
 
 /// Returns whether two objects are structurally equivalent.
 ///
 /// This considers `NaN` values to be equivalent. It also handles
 /// self-referential structures.
-bool deepEquals(obj1, obj2, [List parents1, List parents2]) {
-  if (identical(obj1, obj2)) return true;
-  if (parents1 == null) {
-    parents1 = [];
-    parents2 = [];
+bool deepEquals(obj1, obj2) => new _DeepEquals().equals(obj1, obj2);
+
+/// A class that provides access to the list of parent objects used for loop
+/// detection.
+class _DeepEquals {
+  final _parents1 = [];
+  final _parents2 = [];
+
+  /// Returns whether [obj1] and [obj2] are structurally equivalent.
+  bool equals(obj1, obj2) {
+    // _parents1 and _parents2 are guaranteed to be the same size.
+    for (var i = 0; i < _parents1.length; i++) {
+      var loop1 = identical(obj1, _parents1[i]);
+      var loop2 = identical(obj2, _parents2[i]);
+      // If both structures loop in the same place, they're equal at that point
+      // in the structure. If one loops and the other doesn't, they're not
+      // equal.
+      if (loop1 && loop2) return true;
+      if (loop1 || loop2) return false;
+    }
+
+    _parents1.add(obj1);
+    _parents2.add(obj2);
+    try {
+      if (obj1 is List && obj2 is List) {
+        return _listEquals(obj1, obj2);
+      } else if (obj1 is Map && obj2 is Map) {
+        return _mapEquals(obj1, obj2);
+      } else if (obj1 is num && obj2 is num) {
+        return _numEquals(obj1, obj2);
+      } else {
+        return obj1 == obj2;
+      }
+    } finally {
+      _parents1.removeLast();
+      _parents2.removeLast();
+    }
   }
 
-  // parents1 and parents2 are guaranteed to be the same size.
-  for (var i = 0; i < parents1.length; i++) {
-    var loop1 = identical(obj1, parents1[i]);
-    var loop2 = identical(obj2, parents2[i]);
-    // If both structures loop in the same place, they're equal at that point in
-    // the structure. If one loops and the other doesn't, they're not equal.
-    if (loop1 && loop2) return true;
-    if (loop1 || loop2) return false;
+  /// Returns whether [list1] and [list2] are structurally equal. 
+  bool _listEquals(List list1, List list2) {
+    if (list1.length != list2.length) return false;
+
+    for (var i = 0; i < list1.length; i++) {
+      if (!equals(list1[i], list2[i])) return false;
+    }
+
+    return true;
   }
 
-  parents1.add(obj1);
-  parents2.add(obj2);
-  try {
-    if (obj1 is List && obj2 is List) {
-      return _listEquals(obj1, obj2, parents1, parents2);
-    } else if (obj1 is Map && obj2 is Map) {
-      return _mapEquals(obj1, obj2, parents1, parents2);
-    } else if (obj1 is num && obj2 is num) {
-      return _numEquals(obj1, obj2);
-    } else {
-      return obj1 == obj2;
+  /// Returns whether [map1] and [map2] are structurally equal. 
+  bool _mapEquals(Map map1, Map map2) {
+    if (map1.length != map2.length) return false;
+
+    for (var key in map1.keys) {
+      if (!map2.containsKey(key)) return false;
+      if (!equals(map1[key], map2[key])) return false;
     }
-  } finally {
-    parents1.removeLast();
-    parents2.removeLast();
+
+    return true;
+  }
+
+  /// Returns whether two numbers are equivalent.
+  ///
+  /// This differs from `n1 == n2` in that it considers `NaN` to be equal to
+  /// itself.
+  bool _numEquals(num n1, num n2) {
+    if (n1.isNaN && n2.isNaN) return true;
+    return n1 == n2;
   }
 }
-
-/// Returns whether [list1] and [list2] are structurally equal. 
-bool _listEquals(List list1, List list2, List parents1, List parents2) {
-  if (list1.length != list2.length) return false;
-
-  for (var i = 0; i < list1.length; i++) {
-    if (!deepEquals(list1[i], list2[i], parents1, parents2)) return false;
-  }
-
-  return true;
-}
-
-/// Returns whether [map1] and [map2] are structurally equal. 
-bool _mapEquals(Map map1, Map map2, List parents1, List parents2) {
-  if (map1.length != map2.length) return false;
-
-  for (var key in map1.keys) {
-    if (!map2.containsKey(key)) return false;
-    if (!deepEquals(map1[key], map2[key], parents1, parents2)) return false;
-  }
-
-  return true;
-}
-
-/// Returns whether two numbers are equivalent.
-///
-/// This differs from `n1 == n2` in that it considers `NaN` to be equal to
-/// itself.
-bool _numEquals(num n1, num n2) {
-  if (n1.isNaN && n2.isNaN) return true;
-  return n1 == n2;
-}