C＃4：动态和可空的＆lt;＆gt;

var promo = new
{
    Text = promo.Value,
    StartDate = (startDate == null) ?
        new Nullable<DateTime>() : 
        new Nullable<DateTime>(DateTime.Parse(startDate.Value)),
    EndDate = (endDate == null) ?
        new Nullable<DateTime>() : 
        new Nullable<DateTime>(DateTime.Parse(endDate.Value))
};

dynamic

private static bool IsPromoActive(dynamic promo)
{
    return /* check StartDate, EndDate */
}

StartDate

EndDate

new Nullable<DateTime>(DateTime.Parse(...))

dynamic

promo

if (promo.StartDate.HasValue && promo.StartDate > DateTime.Today ||
    promo.EndDate.HasValue && promo.EndDate < DateTime.Today)
{
    return;
}

Server Error in '/' Application.
'System.DateTime' does not contain a definition for 'HasValue' 

Nullable

dynamic

struct

StartDate

StartDate

EndDate

dynamic