"C# extension methods to save the day" article - 29/11/2020

ARecordWithExtensionMethods.cs

void Main() {
  var person = new Person {
    FirstName = "Konstantinos",
    LastName = "Grevenits"
  };

  Console.WriteLine($ "{person.FirstName} {person.LastName}");
  Console.WriteLine(person.Uppercase());
  Console.WriteLine(person.Lowercase());
}

public record Person {
  public string ? FirstName {
    get;
    init;
  }
  public string ? LastName {
    get;
    init;
  }
}

public static class RecordExtensions {
  public static string Uppercase(this Person person) {
    return $ "{person.FirstName} {person.LastName}".ToUpper();
  }

  public static string Lowercase(this Person person) {
    return $ "{person.FirstName} {person.LastName}".ToLower();
  }
}

EnumerationsWithExtensionMethods.cs

using System;
using System.Text;

public enum Season {
  Spring,
  Summer,
  Autumn,
  Winter
}

namespace Seasons {
  class Program {
    static void Main(string[] args) {
      Console.OutputEncoding = System.Text.Encoding.UTF8;
      Console.Write("\xfeff"); // bom = byte order mark

      Console.WriteLine("Spring");
      Console.WriteLine(Season.Spring.SeasonEmoji());

      Console.WriteLine("Summer");
      Console.WriteLine(Season.Summer.SeasonEmoji());

      Console.WriteLine("Winter");
      Console.WriteLine(Season.Winter.SeasonEmoji());

      Console.WriteLine("Autumn");
      Console.WriteLine(Season.Autumn.SeasonEmoji());
    }
  }

  public static class SeasonExtensions {
    public static string SeasonEmoji(this Season season) {
      var emoji = "";

      switch (season) {
      case Season.Spring:
        {
          emoji = "🌳";
          break;
        }

      case Season.Summer:
        {
          emoji = "☀️";
          break;
        }

      case Season.Winter:
        {
          emoji = "❄️";
          break;
        }

      case Season.Autumn:
        {
          emoji = "🍂";
          break;
        }
      }
      return emoji;
    }
  }
}

InterfacesWithExtensionMethods.cs

void Main() {
  var myFile = new MyFile();
  var data = new byte[0]; //or whatever

  myFile.ToDisk(data, "_YOUR_PATH_");
  myFile.ToMemory(data);
}
public class MyFile: IFile {
  public void Save(byte[] fileData, Stream stream) {
    //whatever
  }
}
public interface IFile {
  void Save(byte[] data, Stream stream);
}
public static class IFileExtensions {
  public static FileInfo ToDisk(this IFile file, byte[] data, string filePath) {
    using(var stream = File.Create(filePath)) {
      file.Save(data, stream);
      return new FileInfo(filePath);
    }
  }
  public static byte[] ToMemory(this IFile file, byte[] data) {
    using(var stream = new MemoryStream()) {
      file.Save(data, stream);
      return stream.ToArray();
    }
  }
}