Uri: use List.unmodifiable

sdk/lib/core/uri.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.
 
 part of dart.core;
 
 /**
  * A parsed URI, such as a URL.
  *
  * **See also:**
@@ skipping 991 matching lines @@
    *
    * If this `Uri` does not have a fragment, it is itself returned.
    */
   Uri removeFragment() {
     if (!this.hasFragment) return this;
     return new Uri._internal(scheme, _userInfo, _host, _port,
                              _path, _query, null);
   }
 
   /**
-   * Returns the URI path split into its segments. Each of the
-   * segments in the returned list have been decoded. If the path is
-   * empty the empty list will be returned. A leading slash `/` does
-   * not affect the segments returned.
+   * Returns the URI path split into its segments. Each of the segments in the
+   * returned list have been decoded. If the path is empty the empty list will
+   * be returned. A leading slash `/` does not affect the segments returned.
    *
    * The returned list is unmodifiable and will throw [UnsupportedError] on any
    * calls that would mutate it.
    */
   List<String> get pathSegments {
-    if (_pathSegments == null) {
-      var pathToSplit = !path.isEmpty && path.codeUnitAt(0) == _SLASH
-                        ? path.substring(1)
-                        : path;
-      _pathSegments = new UnmodifiableListView(
-        pathToSplit == "" ? const<String>[]
-                          : pathToSplit.split("/")
-                                       .map(Uri.decodeComponent)
-                                       .toList(growable: false));
+    var result = _pathSegments;
+    if (result != null) return result;
+
+    var pathToSplit = path;
+    if (pathToSplit.isNotEmpty && pathToSplit.codeUnitAt(0) == _SLASH) {
+      pathToSplit = pathToSplit.substring(1);
     }
-    return _pathSegments;
+    result = (pathToSplit == "")
+        ? const<String>[]
+        : new List<String>.unmodifiable(
+              pathToSplit.split("/").map(Uri.decodeComponent));
+    _pathSegments = result;
+    return result;
   }
 
   /**
    * Returns the URI query split into a map according to the rules
    * specified for FORM post in the [HTML 4.01 specification section 17.13.4]
    * (http://www.w3.org/TR/REC-html40/interact/forms.html#h-17.13.4
    * "HTML 4.01 section 17.13.4"). Each key and value in the returned map
    * has been decoded. If there is no query the empty map is returned.
    *
    * Keys in the query string that have no value are mapped to the
@@ skipping 1569 matching lines @@
       0xafff,   // 0x30 - 0x3f  1111111111110101
                 //              @ABCDEFGHIJKLMNO
       0xffff,   // 0x40 - 0x4f  1111111111111111
                 //              PQRSTUVWXYZ    _
       0x87ff,   // 0x50 - 0x5f  1111111111100001
                 //               abcdefghijklmno
       0xfffe,   // 0x60 - 0x6f  0111111111111111
                 //              pqrstuvwxyz   ~
       0x47ff];  // 0x70 - 0x7f  1111111111100010
 }