NCrontab demo showing direct use of CrontabField

NCrontabFieldsDemo.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp3.1</TargetFramework>
    <RootNamespace></RootNamespace>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="ncrontab" Version="3.3.1" />
  </ItemGroup>

</Project>

Program.cs

#nullable enable

using System;
using System.Collections.Generic;
using System.Linq;
using NCrontab;

// See also: https://github.com/atifaziz/NCrontab/issues/71

static class Program
{
    static readonly (CrontabFieldKind Kind, Func<string, CrontabField> Parser)[] CrontabFields =
    {
        (CrontabFieldKind.Second   , CrontabField.Seconds   ),
        (CrontabFieldKind.Minute   , CrontabField.Minutes   ),
        (CrontabFieldKind.Hour     , CrontabField.Hours     ),
        (CrontabFieldKind.Day      , CrontabField.Days      ),
        (CrontabFieldKind.Month    , CrontabField.Months    ),
        (CrontabFieldKind.DayOfWeek, CrontabField.DaysOfWeek),
    };

    static void Main(string[] args)
    {
        if (args.Length == 0)
            throw new Exception("Missing crontab expression argument.");

        var expressions = args[0].Split(' ', StringSplitOptions.RemoveEmptyEntries);
        if (expressions.Length < 5 || expressions.Length > 6)
            throw new Exception("Invalid crontab expression field count (must be 5 or 6).");

        foreach (var (expr, (kind, parser)) in
                 expressions.Zip(CrontabFields.TakeLast(expressions.Length)))
        {
            var field = parser(expr);
            Console.WriteLine($"{expr} : {kind} = {string.Join(", ", field.Values())}");
        }
    }

    static IEnumerable<int> Values(this ICrontabField field)
    {
        for (var n = field.GetFirst(); n >= 0; n = field.Next(n + 1))
            yield return n;
    }
}