Implement equality for 'ContrabSchedule'

[julealgon]

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.

[atifaziz]

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:

https://github.com/atifaziz/NCrontab/blob/b6659e45d60de554c5619d7f35f39ad1114b6542/NCrontab/CrontabSchedule.cs#L376-L397

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.