Create an interface with a method that's 'generic', but it's generic type is the implementer of the interface

Is there any way in C# to have a generic type that is always the implementing type in an interface?

No. The answers given so far don't satisfy this, for two reasons:

• You can always implement an interface with a different T

  interface IFoo<T>
  {
      T GetOtherThis();
  }
  
  public class NotAString : Foo<string>
  {
      string GetOtherThis() { ... }
  }
  

  This can be fixed somewhere with a constraint: interface IFoo<T> where T : IFoo<T> but that still doesn't stop this;

  public class Good : IFoo<Good> { ... }
  
  public class Evil : IFoo<Good> { /* Mwahahahaha */ }
  

• Inheritance breaks it anyway:

  interface IFoo<T>
  {
      T GetOtherThis();
  }
  
  public class WellBehaved : IFoo<WellBehaved>
  {
      WellBehaved GetOtherThis() { ... }
  }
  
  public class BadlyBehaved : WellBehaved
  {
      // Ha! Now x.GetOtherThis().GetType() != x.GetType()
  }
  

Basically there's nothing in C# which will enforce this for you. If you trust interface implementations to be sensible, then the generic interface scheme is still useful, but you need to understand its limitations.