interval 
Provides the Interval class, a contiguous set of values.
If an Interval contains two values, it also contains all values between them. It may have an upper and lower bound, and those bounds may be open or closed.
##Install
pub global activate den # If you haven't already
den install interval##Usage
import 'package:interval/interval.dart';
// Date intervals
var activeDates = new Interval<DateTime>.closed(date1, date2);
if(activeDates.contains(new DateTime.now()) {
print('Item is active!');
}
// View selection model
var slider = new Slider(interval: new Interval.closed(0, 100));
// Validation
class Rating {
final int value;
Rating(this.value) {
if(!new Interval.closed(1, 5).contains(value)) {
throw new ArgumentError('ratings must be between 1 and 5');
}
}
}