How to Implement a Generic Interface in a Non-generic Class in C#

Learning Objective

• How to create generic interfaces of type T
• How to implement a generic interface in a non-generic class
• How to implement a generic interface in a generic class

Prerequisites

Please review the basic concepts of generics to understand the article better.

Getting Started

Let us understand how to create an interface of type T. A blank interface will look like this.

public interface ITest<T> { }

An interface with one member function definition

public interface ITest<T> {
   List<T> GetList();
}

The syntax for multiple generic values for an interface

public interface ITest<T, U>{
  List<T> GetList(U value);
}

After understanding the basic syntax for interfaces with single or numerous generic types. Let's see how to implement them in a class.

Implementation in a non-generic class

The implementation is divided into two cases:

Case 1: Single generic type interface with non-generic class

The below example shows if we do not define the “T” type. Please refer ITest<T> definition above.

public class Test : ITest<T>{
  public List<T> GetList(){}
}

The compiler will throw an exception that it cannot understand the reference of T.

Solution: Let’s define the type “T.”

public class Test : ITest<int>{
   public List<int> GetList(){return null;}
}

Case 2: Multiple generic type interface with non-generic class

In the case of non-generic classes, as mentioned above, we must define the genetic types. Please refer ITest<T,U> definition above.

public class Test : ITest<int, int>{
   public List<int> GetList(int value){return null;}
}

Implementation in a generic class

The implementation is again divided into two cases:

Case 1: Single generic type interface with a generic class

Please refer ITest<T> definition above.

public class Test<T> : ITest<T>{
  public List<T> GetList(){return null;}
}

Case 2: Multiple generic type interface with a generic class

Please refer ITest<T,U> definition above.

public class Test<T, U> : ITest<T, U>{
   public List<T> GetList(U value){return null;}
}

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