Document equality and compareTo of numbers.

runtime/lib/double.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.
 
 class _Double implements double {
   factory _Double.fromInteger(int value)
       native "Double_doubleFromInteger";
 
   Type get runtimeType => double;
 
@@ skipping 193 matching lines @@
     if (isNaN) return "NaN";
     if (this == double.INFINITY) return "Infinity";
     if (this == -double.INFINITY) return "-Infinity";
 
     return _toStringAsPrecision(precision);
   }
   String _toStringAsPrecision(int fractionDigits)
       native "Double_toStringAsPrecision";
 
   // Order is: NaN > Infinity > ... > 0.0 > -0.0 > ... > -Infinity.
-  int compareTo(Comparable other) {
+  int compareTo(num other) {
     final int EQUAL = 0, LESS = -1, GREATER = 1;
     if (this < other) {
       return LESS;
     } else if (this > other) {
       return GREATER;
     } else if (this == other) {
       if (this == 0.0) {
         bool thisIsNegative = isNegative;
         bool otherIsNegative = other.isNegative;
         if (thisIsNegative == otherIsNegative) {
           return EQUAL;
         }
         return thisIsNegative ? LESS : GREATER;
       } else {
         return EQUAL;
       }
     } else if (isNaN) {
       return other.isNaN ? EQUAL : GREATER;
     } else {
       // Other is NaN.
       return LESS;
     }
   }
 }