Implement equality for 'ContrabSchedule'

[Juliano Leal Goncalves]

There is currently no way to check a ContrabSchedule object for equality against another schedule. It's also not possible to properly implement a custom EqualityComparer from the outside since the fields that store the data inside the schedule are all private.

This could be fixed by implementing IEquatable<ContrabSchedule> on the model.

[Atif Aziz]

I'll think about this but meanwhile…

There is currently no way to check a ContrabSchedule object for equality against another schedule.

The ToString() implementation of ContrabSchedule returns an expanded/lowered version of the one originally parsed expression:

NCrontab/NCrontab/CrontabSchedule.cs

Lines 376 to 397 in b6659e4

 /// <summary> 
 /// Returns a string in crontab expression (expanded) that represents 
 /// this schedule. 
 /// </summary> 
  
 public override string ToString() 
 { 
     var writer = new StringWriter(CultureInfo.InvariantCulture); 
  
     if (_seconds != null) 
     { 
         _seconds.Format(writer, true); 
         writer.Write(' '); 
     } 
     _minutes.Format(writer, true); writer.Write(' '); 
     _hours.Format(writer, true); writer.Write(' '); 
     _days.Format(writer, true); writer.Write(' '); 
     _months.Format(writer, true); writer.Write(' '); 
     _daysOfWeek.Format(writer, true); 
  
     return writer.ToString(); 
 } 

It can be used today as a good basis for equality comparison via an IEqualityComparer<CrontabSchedule> implementation like so:

sealed class EqualityComparer<CrontabSchedule> : IEqualityComparer<CrontabSchedule>
{
    public bool Equals(CrontabSchedule x, CrontabSchedule y) =>
        x?.ToString() == y?.ToString();

    public int GetHashCode(CrontabSchedule obj) =>
        obj.ToString().GetHashCode();
}

Usage would then be:

var comparer = new EqualityComparer<CrontabSchedule>();
var schedule1 = CrontabSchedule.Parse("0-59 * * * Mon-Fri/2");
var schedule2 = CrontabSchedule.Parse("* * * * Fri,Mon,Wed");
var schedule3 = CrontabSchedule.Parse("* * * * *");
Console.WriteLine(comparer.Equals(schedule1, schedule2)); // True
Console.WriteLine(comparer.Equals(schedule1, schedule3)); // False
Console.WriteLine(comparer.Equals(schedule2, schedule3)); // False

Note how 0-59 * * * Mon-Fri/2 (schedule1) and * * * * Fri,Mon,Wed (schedule2) compare equal even though they are expressed differently.