Redo "Fast path constructor for 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 span of time, such as 27 days, 4 hours, 12 minutes, and 3 seconds.
  *
  * A `Duration` represents a difference from one point in time to another. The
@@ skipping 74 matching lines @@
    *
    * All individual parts are allowed to be negative.
    * All arguments are 0 by default.
    */
   const Duration({int days: 0,
                   int hours: 0,
                   int minutes: 0,
                   int seconds: 0,
                   int milliseconds: 0,
                   int microseconds: 0})
-      : _duration = days * MICROSECONDS_PER_DAY +
-                    hours * MICROSECONDS_PER_HOUR +
-                    minutes * MICROSECONDS_PER_MINUTE +
-                    seconds * MICROSECONDS_PER_SECOND +
-                    milliseconds * MICROSECONDS_PER_MILLISECOND +
-                    microseconds;
+      : this._microseconds(
+            days * MICROSECONDS_PER_DAY +
+            hours * MICROSECONDS_PER_HOUR +
+            minutes * MICROSECONDS_PER_MINUTE +
+            seconds * MICROSECONDS_PER_SECOND +
+            milliseconds * MICROSECONDS_PER_MILLISECOND +
+            microseconds);
+
+  // Fast path internal direct constructor to avoids the optional arguments and
+  // [_microseconds] recomputation.
+  const Duration._microseconds(this._duration);
 
   /**
    * Adds this Duration and [other] and
    * returns the sum as a new Duration object.
    */
   Duration operator +(Duration other) {
-    return new Duration(microseconds: _duration + other._duration);
+    return new Duration._microseconds(_duration + other._duration);
   }
 
   /**
    * Subtracts [other] from this Duration and
    * returns the difference as a new Duration object.
    */
   Duration operator -(Duration other) {
-    return new Duration(microseconds: _duration - other._duration);
+    return new Duration._microseconds(_duration - other._duration);
   }
 
   /**
    * Multiplies this Duration by the given [factor] and returns the result
    * as a new Duration object.
    *
    * Note that when [factor] is a double, and the duration is greater than
    * 53 bits, precision is lost because of double-precision arithmetic.
    */
   Duration operator *(num factor) {
-    return new Duration(microseconds: (_duration * factor).round());
+    return new Duration._microseconds((_duration * factor).round());
   }
 
   /**
    * Divides this Duration by the given [quotient] and returns the truncated
    * result as a new Duration object.
    *
    * 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(microseconds: _duration ~/ quotient);
+    return new Duration._microseconds(_duration ~/ quotient);
   }
 
   /**
    * Returns `true` if the value of this Duration
    * is less than the value of [other].
    */
   bool operator <(Duration other) => this._duration < other._duration;
 
   /**
    * Returns `true` if the value of this Duration
@@ skipping 91 matching lines @@
       if (n >= 100) return "000$n";
       if (n >= 10) return "0000$n";
       return "00000$n";
     }
     String twoDigits(int n) {
       if (n >= 10) return "$n";
       return "0$n";
     }
 
     if (inMicroseconds < 0) {
-      Duration duration =
-          new Duration(microseconds: -inMicroseconds);
-      return "-$duration";
+      return "-${-this}";
     }
     String twoDigitMinutes = twoDigits(inMinutes.remainder(MINUTES_PER_HOUR));
     String twoDigitSeconds = twoDigits(inSeconds.remainder(SECONDS_PER_MINUTE));
     String sixDigitUs =
         sixDigits(inMicroseconds.remainder(MICROSECONDS_PER_SECOND));
     return "$inHours:$twoDigitMinutes:$twoDigitSeconds.$sixDigitUs";
   }
 
   /**
    * Returns whether this `Duration` is negative.
    *
    * A negative `Duration` represents the difference from a later time to an
    * earlier time.
    */
   bool get isNegative => _duration < 0;
 
   /**
    * Returns a new `Duration` representing the absolute value of this
    * `Duration`.
    *
    * The returned `Duration` has the same length as this one, but is always
    * positive.
    */
-  Duration abs() => new Duration(microseconds: _duration.abs());
+  Duration abs() => new Duration._microseconds(_duration.abs());
 
   /**
    * Returns a new `Duration` representing this `Duration` negated.
    *
    * The returned `Duration` has the same length as this one, but will have the
    * opposite sign of this one.
    */
-  Duration operator -() => new Duration(microseconds: -_duration);
+  Duration operator -() => new Duration._microseconds(-_duration);
 }