有些时候我们需要判断某个类型是否是Nullable类型，并且可能需要知道它的原始类型，
比如在做些ORM相关工作时，就需要这方面的应用，如下代码使用可以实现这个要求

class Program
    {
        static void Main( string[] args )
        {
            RL( );


        Type type =  typeof( DateTime? );
        Type originalType;

        if ( IsNullable( type , out originalType ) )
        {
            WL( originalType.ToString( ) );
        }
        else
        {
            WL( "NOT Nullable" );
        }

        type =  typeof( DateTime );

        if ( IsNullable( type , out originalType ) )
        {
            WL( originalType.ToString( ) );
        }
        else
        {
            WL( "NOT Nullable" );
        }

        RL( );
    }

    private static bool IsNullable( Type p , out Type originalType )
    {
        bool result = false;

        if ( p.IsGenericType && p.GetGenericTypeDefinition( ) == typeof( Nullable<> ) )
        {
            result = true;
            originalType = p.GetGenericArguments( )[0];
        }
        else
        {
            originalType = null;
        }

        return result;
    }

    #region Helper methods

    private static void WL( object text , params object[] args )
    {
        Console.WriteLine( text.ToString( ) , args );
    }

    private static void RL( )
    {
        Console.ReadLine( );
    }

    private static void Break( )
    {
        System.Diagnostics.Debugger.Break( );
    }

    #endregion
}