Question

Why are static indexers disallowed in C#? I see no reason why they should not be allowed and furthermore they could be very useful.

For example:

public static class ConfigurationManager  {         public object this[string name]         {             get => ConfigurationManager.getProperty(name);             set => ConfigurationManager.editProperty(name, value);         }          /// <summary>         /// This will write the value to the property. Will overwrite if the property is already there         /// </summary>         /// <param name='name'>Name of the property</param>         /// <param name='value'>Value to be wrote (calls ToString)</param>         public static void editProperty(string name, object value)          {             var ds = new DataSet();             var configFile = new FileStream('./config.xml', FileMode.OpenOrCreate);             ds.ReadXml(configFile);              if (ds.Tables['config'] == null)                 ds.Tables.Add('config');              var config = ds.Tables['config'];              if (config.Rows[0] == null)                  config.Rows.Add(config.NewRow());              if (config.Columns[name] == null)                  config.Columns.Add(name);              config.Rows[0][name] = value.ToString();              ds.WriteXml(configFile);             configFile.Close();         }          public static void addProperty(string name, object value) =>             ConfigurationManager.editProperty(name, value);          public static object getProperty(string name)          {             var ds = new DataSet();             var configFile = new FileStream('./config.xml', FileMode.OpenOrCreate);             ds.ReadXml(configFile);             configFile.Close();              if (ds.Tables['config'] == null) return null;              var config = ds.Tables['config'];              if (config.Rows[0] == null) return null;             if (config.Columns[name] == null) return null;              return config.Rows[0][name];         }     } 

The above code would benefit greatly from a static indexer. However it won’t compile because static indexers are not allowed. Why is this so?

Answer 1

Indexer notation requires a reference to this. Since static methods don’t have a reference to any particular instance of the class, you can’t use this with them, and consequently you can’t use indexer notation on static methods.

The solution to your problem is using a singleton pattern as follows:

public class Utilities {     private static ConfigurationManager _configurationManager = new ConfigurationManager();     public static ConfigurationManager ConfigurationManager => _configurationManager; }  public class ConfigurationManager {     public object this[string value]     {         get => new object();         set => // set something     } } 

Now you can call Utilities.ConfigurationManager['someKey'] using indexer notation.