什么是好的代码

xaut3 · 发表于 2010-5-6 07:59:15

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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 + "'");
}
}

看看CreatePO()和ReadPO()，多么地冗长。虽然这个实现极为简单，但对于代码的阅读者而言，想要一下子抓住该方法的中心思想，仍然比较困难。此外，方法中的注释也显得多余，因为，代码本身就可以给予很好的说明。
下面，是我对这段代码的重构，大家可以对比对比，是否更加容易阅读呢？ public static class PurchaseOrderHandler {
      public static void CreatePurchaseOrder(string filename) {
         PurchaseOrder po = BuildPurchaseOrder();
         XmlSerializer serializer = new XmlSerializer(typeof(PurchaseOrder));
         using (var writer = new StreamWriter(filename)) {
            serializer.Serialize(writer, po);
         }
      }

      private static PurchaseOrder BuildPurchaseOrder() {
         Address address = CreateAddress();
         OrderedItem i1 = CreateOrderedItem();
         OrderedItem[] items = { i1 };

         PurchaseOrder po = new PurchaseOrder();
         po.ShipTo = address;
         po.OrderDate = System.DateTime.Now.ToLongDateString();
         po.OrderedItems = items;
         po.SubTotal = CalculateSubTotal(items);
         po.ShipCost = (decimal)12.51;
         po.TotalCost = po.SubTotal + po.ShipCost;

         return po;
      }

      private static decimal CalculateSubTotal(OrderedItem[] items) {
         decimal subTotal = new decimal();
         foreach (OrderedItem oi in items) {
            subTotal += oi.LineTotal;
         }

         return subTotal;
      }

      private static OrderedItem CreateOrderedItem() {
         OrderedItem i1 = new OrderedItem();
         i1.ItemName = "Widget S";
         i1.Description = "Small widget";
         i1.UnitPrice = (decimal)5.23;
         i1.Quantity = 3;
         i1.Calculate();
         return i1;
      }

      private static Address CreateAddress() {
         Address billAddress = new Address();
         billAddress.Name = "Bruce Zhang";
         billAddress.Line1 = "1 Main St.";
         billAddress.City = "Chong Qing";
         billAddress.State = "Chong Qing";
         billAddress.Zip = "400000";

         return billAddress;
      }

      public static void ReadPurchaseOrder(string filename) {
         XmlSerializer serializer = new XmlSerializer(typeof(PurchaseOrder));

         serializer.UnknownNode += new XmlNodeEventHandler(serializer_UnknownNode);
         serializer.UnknownAttribute += new XmlAttributeEventHandler(serializer_UnknownAttribute);

         FileStream fs = new FileStream(filename, FileMode.Open);

         PurchaseOrder po;
         po = (PurchaseOrder)serializer.Deserialize(fs);
         PurchaseOrderPrinter.PrintPurchaseOrder(po);
      }

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

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

      private static class PurchaseOrderPrinter {
         public static void PrintPurchaseOrder(PurchaseOrder po) {
            PrintOrderDate(po);
            PrintAddress(po.ShipTo);
            PrintOrderedItem(po.OrderedItems);
            PrintOrderCost(po);
         }

         private static void PrintOrderCost(PurchaseOrder po) {
            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);
         }

         private static void PrintOrderDate(PurchaseOrder po) {
            Console.WriteLine("OrderDate: " + po.OrderDate);
         }

         private static void PrintOrderedItem(OrderedItem[] items) {
            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);
            }
         }

         private static void PrintAddress(Address a) {
            // Read the fields of the Address object.
            Console.WriteLine("Ship To:");
            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();
         }
      }
}

阅读代码时，我们可以先关注最主要的方法，即CreatePurchaseOrder()和ReadPurchaseOrder()方法。如果并不希望了解过多构造PO对象的细节，通过阅读这样简短的方法，可以很容易地抓住这两个方法的实现，那就是通过构建一个PO对象，进行序列化，而在反序列化时，将获得的PO对象信息打印出来。
其实，糟糕的代码不一定就是初学者的“专利”，让我们看看NHibernate中的一段代码：public SessionFactoryImpl(Configuration cfg, IMapping mapping, Settings settings, EventListeners listeners)
{
Init();
log.Info("building session factory");

properties = new Dictionary<string, string>(cfg.Properties);
interceptor = cfg.Interceptor;
this.settings = settings;
sqlFunctionRegistry = new SQLFunctionRegistry(settings.Dialect, cfg.SqlFunctions);
eventListeners = listeners;
filters = new Dictionary<string, FilterDefinition>(cfg.FilterDefinitions);
if (log.IsDebugEnabled)
{
      log.Debug("Session factory constructed with filter configurations : " + CollectionPrinter.ToString(filters));
}

if (log.IsDebugEnabled)
{
      log.Debug("instantiating session factory with properties: " + CollectionPrinter.ToString(properties));
}

try
{
      if (settings.IsKeywordsImportEnabled)
      {
         SchemaMetadataUpdater.Update(this);
      }
      if (settings.IsAutoQuoteEnabled)
      {
         SchemaMetadataUpdater.QuoteTableAndColumns(cfg);
      }
}
catch (NotSupportedException)
{
      // Ignore if the Dialect does not provide DataBaseSchema
}

#region Caches
settings.CacheProvider.Start(properties);
#endregion

#region Generators
identifierGenerators = new Dictionary<string, IIdentifierGenerator>();
foreach (PersistentClass model in cfg.ClassMappings)
{
      if (!model.IsInherited)
      {
         IIdentifierGenerator generator =
            model.Identifier.CreateIdentifierGenerator(settings.Dialect, settings.DefaultCatalogName,
                                                         settings.DefaultSchemaName, (RootClass) model);

         identifierGenerators[model.EntityName] = generator;
      }
}
#endregion

#region Persisters

Dictionary<string, ICacheConcurrencyStrategy> caches = new Dictionary<string, ICacheConcurrencyStrategy>();
entityPersisters = new Dictionary<string, IEntityPersister>();
implementorToEntityName = new Dictionary<System.Type, string>();

Dictionary<string, IClassMetadata> classMeta = new Dictionary<string, IClassMetadata>();

foreach (PersistentClass model in cfg.ClassMappings)
{
      model.PrepareTemporaryTables(mapping, settings.Dialect);
      string cacheRegion = model.RootClazz.CacheRegionName;
      ICacheConcurrencyStrategy cache;
      if (!caches.TryGetValue(cacheRegion, out cache))
      {
         cache =
            CacheFactory.CreateCache(model.CacheConcurrencyStrategy, cacheRegion, model.IsMutable, settings, properties);
         if (cache != null)
         {
            caches.Add(cacheRegion, cache);
            allCacheRegions.Add(cache.RegionName, cache.Cache);
         }
      }
      IEntityPersister cp = PersisterFactory.CreateClassPersister(model, cache, this, mapping);
      entityPersisters[model.EntityName] = cp;
      classMeta[model.EntityName] = cp.ClassMetadata;

      if (model.HasPocoRepresentation)
      {
         implementorToEntityName[model.MappedClass] = model.EntityName;
      }
}
classMetadata = new UnmodifiableDictionary<string, IClassMetadata>(classMeta);

Dictionary<string, ISet<string>> tmpEntityToCollectionRoleMap = new Dictionary<string, ISet<string>>();
collectionPersisters = new Dictionary<string, ICollectionPersister>();
foreach (Mapping.Collection model in cfg.CollectionMappings)
{
      ICacheConcurrencyStrategy cache =
         CacheFactory.CreateCache(model.CacheConcurrencyStrategy, model.CacheRegionName, model.Owner.IsMutable, settings,
                                 properties);
      if (cache != null)
      {
         allCacheRegions[cache.RegionName] = cache.Cache;
      }
      ICollectionPersister persister = PersisterFactory.CreateCollectionPersister(cfg, model, cache, this);
      collectionPersisters[model.Role] = persister;
      IType indexType = persister.IndexType;
      if (indexType != null && indexType.IsAssociationType && !indexType.IsAnyType)
      {
         string entityName = ((IAssociationType) indexType).GetAssociatedEntityName(this);
         ISet<string> roles;
         if (!tmpEntityToCollectionRoleMap.TryGetValue(entityName, out roles))
         {
            roles = new HashedSet<string>();
            tmpEntityToCollectionRoleMap[entityName] = roles;
         }
         roles.Add(persister.Role);
      }
      IType elementType = persister.ElementType;
      if (elementType.IsAssociationType && !elementType.IsAnyType)
      {
         string entityName = ((IAssociationType) elementType).GetAssociatedEntityName(this);
         ISet<string> roles;
         if (!tmpEntityToCollectionRoleMap.TryGetValue(entityName, out roles))
         {
            roles = new HashedSet<string>();
            tmpEntityToCollectionRoleMap[entityName] = roles;
         }
         roles.Add(persister.Role);
      }
}
Dictionary<string, ICollectionMetadata> tmpcollectionMetadata = new Dictionary<string, ICollectionMetadata>(collectionPersisters.Count);
foreach (KeyValuePair<string, ICollectionPersister> collectionPersister in collectionPersisters)
{
      tmpcollectionMetadata.Add(collectionPersister.Key, collectionPersister.Value.CollectionMetadata);
}
collectionMetadata = new UnmodifiableDictionary<string, ICollectionMetadata>(tmpcollectionMetadata);
collectionRolesByEntityParticipant = new UnmodifiableDictionary<string, ISet<string>>(tmpEntityToCollectionRoleMap);
#endregion

#region Named Queries
namedQueries = new Dictionary<string, NamedQueryDefinition>(cfg.NamedQueries);
namedSqlQueries = new Dictionary<string, NamedSQLQueryDefinition>(cfg.NamedSQLQueries);
sqlResultSetMappings = new Dictionary<string, ResultSetMappingDefinition>(cfg.SqlResultSetMappings);
#endregion

imports = new Dictionary<string, string>(cfg.Imports);

#region after *all* persisters and named queries are registered
foreach (IEntityPersister persister in entityPersisters.Values)
{
      persister.PostInstantiate();
}
foreach (ICollectionPersister persister in collectionPersisters.Values)
{
      persister.PostInstantiate();
}
#endregion

#region Serialization info

name = settings.SessionFactoryName;
try
{
      uuid = (string) UuidGenerator.Generate(null, null);
}
catch (Exception)
{
      throw new AssertionFailure("Could not generate UUID");
}

SessionFactoryObjectFactory.AddInstance(uuid, name, this, properties);

#endregion

log.Debug("Instantiated session factory");

#region Schema management
if (settings.IsAutoCreateSchema)
{
      new SchemaExport(cfg).Create(false, true);
}

if ( settings.IsAutoUpdateSchema )
{
      new SchemaUpdate(cfg).Execute(false, true);
}
if (settings.IsAutoValidateSchema)
{
      new SchemaValidator(cfg, settings).Validate();
}
if (settings.IsAutoDropSchema)
{
      schemaExport = new SchemaExport(cfg);
}
#endregion

#region Obtaining TransactionManager
// not ported yet

#endregion

currentSessionContext = BuildCurrentSessionContext();

if (settings.IsQueryCacheEnabled)
{
      updateTimestampsCache = new UpdateTimestampsCache(settings, properties);
      queryCache = settings.QueryCacheFactory.GetQueryCache(null, updateTimestampsCache, settings, properties);
      queryCaches = new ThreadSafeDictionary<string, IQueryCache>(new Dictionary<string, IQueryCache>());
}
else
{
      updateTimestampsCache = null;
      queryCache = null;
      queryCaches = null;
}

#region Checking for named queries
if (settings.IsNamedQueryStartupCheckingEnabled)
{
      IDictionary<string, HibernateException> errors = CheckNamedQueries();
      if (errors.Count > 0)
      {
         StringBuilder failingQueries = new StringBuilder("Errors in named queries: ");
         foreach (KeyValuePair<string, HibernateException> pair in errors)
         {
            failingQueries.Append('{').Append(pair.Key).Append('}');
            log.Error("Error in named query: " + pair.Key, pair.Value);
         }
         throw new HibernateException(failingQueries.ToString());
      }
}
#endregion

Statistics.IsStatisticsEnabled = settings.IsStatisticsEnabled;

// EntityNotFoundDelegate
IEntityNotFoundDelegate enfd = cfg.EntityNotFoundDelegate;
if (enfd == null)
{
      enfd = new DefaultEntityNotFoundDelegate();
}
entityNotFoundDelegate = enfd;
}

这是类SessionFactoryImpl（它实现了ISessionFactoryImplementor接口）的构造函数，其目的时是通过Configuration以及Setting中的某些值，去初始化SessionFactoryImpl，然后构建该类的对象。坦白说，我从来没有看过如此“浩瀚无垠”的构造函数。幸好，Visual Studio提高了Region，否则，更让人头疼。（我在想，既然代码的编写者已经利用了Region来分割实现，为何不进一步将其分割为小的方法呢？）
看这样的代码，我们能够轻易读懂吗？
拙劣代码可谓遗患无穷。在《程序员修炼之道》一书中，提到了所谓“破窗效应”，即“没修复的破窗，导致更多的窗户被打破”。丑陋的代码如果只有一个小的片段，看似无关紧要，就像一幢大楼的一扇破窗一般容易让人忘记。随着时间的推移，当这些丑陋代码不知不觉蔓延到整个项目中时，我们才发现这一幢大楼已经满目疮痍了。“一屋不扫，何以扫天下”，程序员应该从小处着手，未来才可能写出优雅的代码。

wsz310 · 发表于 2010-5-6 09:07:50

写得好，但做到确实很难

hgn2007 · 发表于 2010-9-5 12:48:12

看看
刚好要用到

gxuyang · 发表于 2010-10-4 16:09:34

版主说的书我好像都没有看过……找个时间阅读一下……我怎么发现现在搞软件计算的人好像不是很多的样子啊

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什么是好的代码

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