using System;

public class Program

{

    public static void Main()

    {

        var r = new FooBarResult(){ IsSuccessful = false };

        var p = r.Payload;

    }

}

​

public class FooBarResult

{

     public bool IsSuccessful {get; set;}

​

     // just doing one to demonstrate

     private string _payload;

     public string Payload

     {

         get { if(IsSuccessful) return _payload; throw new InvalidOperationException(); }

         set { _payload = value; }

     }

}