C#泛型

protected string Vf(object obj, string formt = "")
{
    if (obj == null || obj == DBNull.Value)
    {
         return formt;
    }
    return obj.ToString();
}

protected T Vf<T>(object obj, T formt) where T : struct
{
     if (obj == null || obj == DBNull.Value)
     {
         return formt;
     }
     return (T)Convert.ChangeType(obj, typeof(T));
}