Add +, - and * to Duration.

sdk/lib/core/duration.dart

 // Copyright (c) 2011, 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 [Duration] represents a time span. A duration can be negative.
  */
 class Duration implements Comparable {
@@ skipping 32 matching lines @@
                   int minutes: 0,
                   int seconds: 0,
                   int milliseconds: 0})
       : inMilliseconds = days * Duration.MILLISECONDS_PER_DAY +
                          hours * Duration.MILLISECONDS_PER_HOUR +
                          minutes * Duration.MILLISECONDS_PER_MINUTE +
                          seconds * Duration.MILLISECONDS_PER_SECOND +
                          milliseconds;
 
   /**
+   * Returns the sum of this [Duration] and [other]  as a new [Duration].
+   */
+  Duration operator +(Duration other) {
+    return new Duration(milliseconds: inMilliseconds + other.inMilliseconds);
+  }
+
+  /**
+   * Returns the difference of this [Duration] and [other] as a new
+   * [Duration].
+   */
+  Duration operator -(Duration other) {
+    return new Duration(milliseconds: inMilliseconds - other.inMilliseconds);
+  }
+
+  /**
+   * Multiplies this [Duration] by the given [factor] and returns the result
+   * as a new [Duration].
+   */
+  Duration operator *(int factor) {
+    return new Duration(milliseconds: inMilliseconds * factor);
+  }
+
+  /**
+   * Divides this [Duration] by the given [quotient] and returns the truncated
+   * result as a new [Duration].
+   *
+   * Throws an [IntegerDivisionByZeroException] if [quotient] is `0`.
+   */
+  Duration operator ~/(int quotient) {
+    // By doing the check here instead of relying on "~/" below we get the
+    // exception even with dart2js.
+    if (quotient == 0) throw new IntegerDivisionByZeroException();
+    return new Duration(milliseconds: inMilliseconds ~/ quotient);
+  }
+
+  bool operator <(Duration other) => this.inMilliseconds < other.inMilliseconds;
+
+  bool operator >(Duration other) => this.inMilliseconds > other.inMilliseconds;
+
+  bool operator <=(Duration other) =>
+      this.inMilliseconds <= other.inMilliseconds;
+
+  bool operator >=(Duration other) =>
+      this.inMilliseconds >= other.inMilliseconds;
+
+  /**
    * This [Duration] in days. Incomplete days are discarded
    */
   int get inDays {
     return inMilliseconds ~/ Duration.MILLISECONDS_PER_DAY;
   }
 
   /**
    * This [Duration] in hours. Incomplete hours are discarded.
    * The returned value can be greater than 23.
    */
@@ skipping 48 matching lines @@
     }
     String twoDigitMinutes =
         twoDigits(inMinutes.remainder(Duration.MINUTES_PER_HOUR));
     String twoDigitSeconds =
         twoDigits(inSeconds.remainder(Duration.SECONDS_PER_MINUTE));
     String threeDigitMs =
         threeDigits(inMilliseconds.remainder(Duration.MILLISECONDS_PER_SECOND));
     return "$inHours:$twoDigitMinutes:$twoDigitSeconds.$threeDigitMs";
   }
 }