什么是好的代码

我希望能够编写优美的代码。

优美的代码就像一篇散文，易懂易读，而且看起来很漂亮。在《代码之美》一书中，收录了Ruby之父松本行宏的一篇文章，名为《把代码当作文章》，大约表达了同样的含义。Thoughtworks的一位工程师在《软件开发沉思录》一书中提出，每个类的方法最好不要超过5行。最初让我感觉很惊诧，继而觉得不可能。虽然这位工程师言之凿凿，提到在自己参与的项目中，所有代码都完全遵循了这一规范，我仍然表示怀疑。最近，阅读了Robert C. Martin的著作《代码整洁之道》（英文版名为Clean Code），看到Uncle Bob演示的代码，真是漂亮极了。仔细一看，这些好的代码在每个方法中大多数都没有超过5行。诀窍在哪里？那就是重构手法中最常用的Extract Method。进一步讲，如果我们能够为每个类与方法以及变量定义出好的名字，代码确实可以变成一篇散文。当然，是英文散文。

今天，我在重温.NET的序列化时，在MSDN上找到一篇演示Xml序列化的示范代码。或许是因为示范代码的缘故，这一段代码写得极其地不优雅，甚至显得有些丑陋：

public class Test {
    public static void Main() {
        // Read and write purchase orders.
        Test t = new Test();
        t.CreatePO("po.xml");
        t.ReadPO("po.xml");
    }

    private void CreatePO(string filename) {
        // Create an instance of the XmlSerializer class;
        // specify the type of object to serialize.
        XmlSerializer serializer =
        new XmlSerializer(typeof(PurchaseOrder));
        TextWriter writer = new StreamWriter(filename);
        PurchaseOrder po = new PurchaseOrder();

        // Create an address to ship and bill to.
        Address billAddress = new Address();
        billAddress.Name = "Teresa Atkinson";
        billAddress.Line1 = "1 Main St.";
        billAddress.City = "AnyTown";
        billAddress.State = "WA";
        billAddress.Zip = "00000";
        // Set ShipTo and BillTo to the same addressee.
        po.ShipTo = billAddress;
        po.OrderDate = System.DateTime.Now.ToLongDateString();

        // Create an OrderedItem object.
        OrderedItem i1 = new OrderedItem();
        i1.ItemName = "Widget S";
        i1.Description = "Small widget";
        i1.UnitPrice = (decimal)5.23;
        i1.Quantity = 3;
        i1.Calculate();

        // Insert the item into the array.
        OrderedItem[] items = { i1 };
        po.OrderedItems = items;
        // Calculate the total cost.
        decimal subTotal = new decimal();
        foreach (OrderedItem oi in items) {
            subTotal += oi.LineTotal;
        }
        po.SubTotal = subTotal;
        po.ShipCost = (decimal)12.51;
        po.TotalCost = po.SubTotal + po.ShipCost;
        // Serialize the purchase order, and close the TextWriter.
        serializer.Serialize(writer, po);
        writer.Close();
    }

    protected void ReadPO(string filename) {
        // Create an instance of the XmlSerializer class;
        // specify the type of object to be deserialized.
        XmlSerializer serializer = new XmlSerializer(typeof(PurchaseOrder));
        /* If the XML document has been altered with unknown
        nodes or attributes, handle them with the
        UnknownNode and UnknownAttribute events.*/
        serializer.UnknownNode += new
        XmlNodeEventHandler(serializer_UnknownNode);
        serializer.UnknownAttribute += new
        XmlAttributeEventHandler(serializer_UnknownAttribute);

        // A FileStream is needed to read the XML document.
        FileStream fs = new FileStream(filename, FileMode.Open);
        // Declare an object variable of the type to be deserialized.
        PurchaseOrder po;
        /* Use the Deserialize method to restore the object's state with
        data from the XML document. */
        po = (PurchaseOrder)serializer.Deserialize(fs);
        // Read the order date.
        Console.WriteLine("OrderDate: " + po.OrderDate);

        // Read the shipping address.
        Address shipTo = po.ShipTo;
        ReadAddress(shipTo, "Ship To:");
        // Read the list of ordered items.
        OrderedItem[] items = po.OrderedItems;
        Console.WriteLine("Items to be shipped:");
        foreach (OrderedItem oi in items) {
            Console.WriteLine("\t" +
            oi.ItemName + "\t" +
            oi.Description + "\t" +
            oi.UnitPrice + "\t" +
            oi.Quantity + "\t" +
            oi.LineTotal);
        }
        // Read the subtotal, shipping cost, and total cost.
        Console.WriteLine("\t\t\t\t\t Subtotal\t" + po.SubTotal);
        Console.WriteLine("\t\t\t\t\t Shipping\t" + po.ShipCost);
        Console.WriteLine("\t\t\t\t\t Total\t\t" + po.TotalCost);
    }

    protected void ReadAddress(Address a, string label) {
        // Read the fields of the Address object.
        Console.WriteLine(label);
        Console.WriteLine("\t" + a.Name);
        Console.WriteLine("\t" + a.Line1);
        Console.WriteLine("\t" + a.City);
        Console.WriteLine("\t" + a.State);
        Console.WriteLine("\t" + a.Zip);
        Console.WriteLine();
    }

    private void serializer_UnknownNode
    (object sender, XmlNodeEventArgs e) {
        Console.WriteLine("Unknown Node:" + e.Name + "\t" + e.Text);
    }

    private void serializer_UnknownAttribute
    (object sender, XmlAttributeEventArgs e) {
        System.Xml.XmlAttribute attr = e.Attr;
        Console.WriteLine("Unknown attribute " +
        attr.Name + "='" + attr.Value + "'");
    }
}