New in .NET 7 (9): Overloading of operators in interfaces from C# 11.0

Since the first version of C#, the programming language has allowed operator overloading. C# 11.0 introduces the ability to define an operator overload in an interface to provide a default or commonality across implementations. Only since C# is 11.0 static abstract allowed in interfaces.

dr Holger Schwichtenberg is Chief Technology Expert at MAXIMAGO, which offers innovation and experience-driven software development, including in highly critical safety-related areas. He is also head of the expert network, which supports numerous medium-sized and large companies with advice and training in the development and operation of software with 38 renowned experts.

An interface with an overloaded operator might look like this:

namespace de.WWWings;
public interface IFlug<TSelf> 
  where TSelf : IFlug<TSelf>
 string AbflugOrt { get; set; }
 double Auslastung { get; }
 DateTime Datum { get; set; }
 long FlugNr { get; set; }
 short FreiePlaetze { get; set; }
 bool Nichtraucherflug { get; set; }
 short Plaetze { get; set; }
 string Route { get; }
 string ZielOrt { get; set; }
 public static abstract Flug operator 
  +(TSelf flug, de.WWWings.PassagierSystem.Passagier pass);

One or the other will ask why the interface has to be generic. The reason for this is simple: you end up wanting one Flug-Object simply with + can add up to a passenger. Without the generic implementation you could only have a variable of type IFlug add to the passenger.

Finally, the implementation of the class still needs the interface implementation : IFlug<Flug>:

namespace de.WWWings
 public partial class Flug : IFlug<Flug>
  /// <summary>
  /// Operatorüberladung fuer die Buchung eines Flugs 
  /// durch Addition eines Flug- und eines Passagier-Objekts.
  /// </summary>
  /// <param name="flug">Flugobjekt</param>
  /// <param name="pass">Passagierobjekt</param>
  /// <returns>Flugobjekt mit hinzugefügten Passagier</returns>
  public static Flug operator +(Flug flug,
                                PassagierSystem.Passagier pass)
   return flug;


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