anchor.diff:  /// Specialization for 'as double?'.
   /// Called from generated code.
   double /*?*/ _asDoubleNullable(object) {
  -  if (object is double) return object;
  +  if (_isNum(object)) return _Utils.asDouble(object);
     if (object == null) return object;
     throw _CastError.forType(object, 'double');
   }
  
positive.code: 
  ///
  class _Utils {
    static int asInt(Object o) => JS('int', '#', o);
    static String asString(Object o) => JS('String', '#', o);
  
    static bool isString(Object o) => JS('bool', 'typeof # == "string"', o);
  
negative.code: /// Specialization for 'as num?'.
  /// Called from generated code.
  num /*?*/ _asNumNullable(object) {
    if (_isNum(object)) return _Utils.asNum(object);
    if (object == null) return object;
    throw _CastError.forType(object, 'num');
  }
  