Roslyn，通过 hostObject 传递值

我正在尝试通过hostObject发送一个类，但显然它不想工作：

using Roslyn.Compilers;
using Roslyn.Compilers.CSharp;
using Roslyn.Scripting;
using Roslyn.Scripting.CSharp;

public class ShippingService
{
    public class ShippingDetails//class that I want to send
    {
        public decimal total { get; set; }
        public int quantity { get; set; }
        public string destination { get; set; }
    }
    public static string ShipingCost(decimal total, int quantity, string destination)
    {
        var details = new ShippingDetails
        {
            total = total,
            quantity = quantity,
            destination = destination
        };
        try
            {
                ScriptEngine roslynEngine = new ScriptEngine();
                Roslyn.Scripting.Session session = roslynEngine.CreateSession(details);
                session.AddReference(details.GetType().Assembly);
                session.AddReference("System.Web");
                session.ImportNamespace("System");
                session.ImportNamespace("System.Web");
                var result = session.Execute("details.destination");
                return result;
            }
        catch (Exception e)
            {
            return e.Message;
            }
        return "";
    }   
}

当我调用函数时，例如"法国"，我应该在结果中得到这个值，但我得到错误：

Roslyn.Compilers.CompilationErrorException： (1,1(： 错误 CS0103： 名称"details"在当前上下文中不存在