static method cannot implement interface method, why?

user_397524 0
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interface IXXX
{
    void Foo();
}

class XXX : IXXX
{
    public static void Foo()
    {
        Console.WriteLine("From XXX");
    }
}


class Program 
{
    static void Main(string[] args)
    {
        XXX.Foo();

    }
}

Compiler error: XXX.Foo() cannot implement an interface member because it is static.

Why can't a static method implement an interface method?

c#
6 Answers

Well, I believe it should allowed in case of generic type parameter. It probably simplified contractual singleton class. Here is an example:

public interface IEntity {
   // some constrains...
  DataRow ObjToRow(object obj);
  object RowToObj(DataRow dr);
}

//T would be any class inherites from IEntity with default contructor signature.
public interface IMyContract {
  T read<T>() where T : IEntity;  
  void write<T>(T object) where T : IEntity;
}

//everything in the class is static
public static class SqlProvider : IMyContract {

  public static T read<T>() where T: IEntity {
    DataRow dr = [reading from database]
    return T.RowToObj(dr);
  }

  //compile error here....
  public static void write<T>(T obj) where T : IEntity {
    DataRow dr = T.ObjToRow(obj);

   [ ... commit data row dr to database ... ]

  }
}

public static class MyAppleEntity : IEntity  {
  [... implement IEntity contract normally ... ]
}

public static class MyOrangeEntity : IEntity {
   [... implement IEntity contract normally ... ]
}

public class MyTest {
  void reading() {
     MyAppleEntity apple = SqlProvider.Read<MyAppleEntity>();
     MyOrangeEntity orange = SqlProvider.Read<MyOrangeEntity>();

     SqlProvider.write<MyAppleEntity>(apple); 
     SqlProvider.write<MyOrangeEntity>(orange);
  } 

}

The only time a type reference implicitly is in the SqlProvider.read() and write() and T is well identity at point of invoke. Without static implementation of interface I'm forced to write like this.

public class MyAppleEntity : IEntity  {
  [... implement IEntity contract normally ... ]
}

  .....

  public T read<T>() where T: IEntity, new() {
    DataRow dr = [reading from database]
    return new T().RowToObj(dr);
  }

Very little different but not quite as elegant.

user_6090810
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