using System;

​

public class SomeClass

{

    public string Key {get; set;}

}

​

public interface ISomeInterface

{

    string Value { get; set; }

    SomeClass SomeClass { get; set;}

}

​

public class SomeInterfaceImplementation : ISomeInterface

{

    public SomeInterfaceImplementation()

    {

        SomeClass = new SomeClass()

        {

            Key = "ABC"

        };

    }

    public string Value { get; set; }

    public SomeClass SomeClass { get; set; }

}

​

public class Program

{

    public static void Main()

    {

        var example = new SomeInterfaceImplementation()

        {

            Value = "A value",

        } as ISomeInterface;

        Console.WriteLine($"{example.SomeClass.Key} has value '{example.Value}'");

    }

}