Question

How would you refactor these two classes to abstract out the similarities? An abstract class? Simple inheritance? What would the refactored class(es) look like?

public class LanguageCode {     /// <summary>     /// Get the lowercase two-character ISO 639-1 language code.     /// </summary>     public readonly string Value;      public LanguageCode(string language)     {         this.Value = new CultureInfo(language).TwoLetterISOLanguageName;     }      public static LanguageCode TryParse(string language)     {         if (language == null)         {             return null;         }          if (language.Length > 2)         {             language = language.Substring(0, 2);         }          try         {             return new LanguageCode(language);         }         catch (ArgumentException)         {             return null;         }     } }  public class RegionCode {     /// <summary>     /// Get the uppercase two-character ISO 3166 region/country code.     /// </summary>     public readonly string Value;      public RegionCode(string region)     {         this.Value = new RegionInfo(region).TwoLetterISORegionName;     }      public static RegionCode TryParse(string region)     {         if (region == null)         {             return null;         }          if (region.Length > 2)         {             region = region.Substring(0, 2);         }          try         {             return new RegionCode(region);         }         catch (ArgumentException)         {             return null;         }     } } 

Answer 1

Unless you have a strong reason for refactoring (because you are going to add more classes like those in near future) the penalty of changing the design for such a small and contrived example would overcome the gain in maintenance or overhead in this scenario. Anyhow here is a possible design based on generic and lambda expressions.

public class TwoLetterCode<T> {     private readonly string value;      public TwoLetterCode(string value, Func<string, string> predicate)     {         this.value = predicate(value);     }      public static T TryParse(string value, Func<string, T> predicate)     {         if (value == null)         {             return default(T);         }          if (value.Length > 2)         {             value = value.Substring(0, 2);         }          try         {             return predicate(value);         }         catch (ArgumentException)         {             return default(T);         }     }      public string Value { get { return this.value; } } }  public class LanguageCode : TwoLetterCode<LanguageCode>  {     public LanguageCode(string language)         : base(language, v => new CultureInfo(v).TwoLetterISOLanguageName)     {     }      public static LanguageCode TryParse(string language)     {         return TwoLetterCode<LanguageCode>.TryParse(language, v => new LanguageCode(v));     } }  public class RegionCode : TwoLetterCode<RegionCode> {     public RegionCode(string language)         : base(language, v => new CultureInfo(v).TwoLetterISORegionName)     {     }      public static RegionCode TryParse(string language)     {         return TwoLetterCode<RegionCode>.TryParse(language, v => new RegionCode(v));     } }