using System;

#nullable enable

​

public interface INullableAlgorithm<in TInput, out TOutput>

    {

        /// <summary>

        /// Computes a value with the algorithm using the given input value(s)

        /// </summary>

        /// <param name="input"></param>

        /// <returns>Value of type <typeparamref name="TOutput"/> or null.</returns>

        TOutput? Put(TInput input);

    }

​

public class TestClass {

​

    public int A {get;set;}

}

​

public struct TestStruct {

​

    public int A {get;set;}

}

​

public class Test : INullableAlgorithm<int, TestClass> {

    public  TestClass? Put(int input) {

        return new TestClass { A = input };

    }

}

​

public class Test2 : INullableAlgorithm<int, TestStruct?> {

    public TestStruct? Put(int input) {

        return new TestStruct { A = input };

    }

}

​

public class Program

{

    public static void Main()

    {

        var algo = new Test();

        var output = algo.Put(2);

        Console.WriteLine(output?.A);

        var algo2 = new Test2();

        var output2 = algo2.Put(2);

        Console.WriteLine(output2?.A);

    }

}