溫馨提示×
您好，登錄后才能下訂單哦！
點(diǎn)擊 登錄注冊(cè) 即表示同意《億速云用戶服務(wù)條款》
您好，登錄后才能下訂單哦！
今天小編給大家分享一下web開(kāi)發(fā)中怎么編寫(xiě)可讀代碼的相關(guān)知識(shí)點(diǎn)，內(nèi)容詳細(xì)，邏輯清晰，相信大部分人都還太了解這方面的知識(shí)，所以分享這篇文章給大家參考一下，希望大家閱讀完這篇文章后有所收獲，下面我們一起來(lái)了解一下吧。
“Code should be written to minimize the time it would take for someone else to understand it.”
日常工作的事實(shí)是：
寫(xiě)代碼前的思考和看代碼的時(shí)間遠(yuǎn)大于真正寫(xiě)的時(shí)間
讀代碼是很平常的事情，不論是別人的，還是自己的，半年前寫(xiě)的可認(rèn)為是別人的代碼
代碼可讀性高，很快就可以理解程序的邏輯，進(jìn)入工作狀態(tài)
行數(shù)少的代碼不一定就容易理解
代碼的可讀性與程序的效率、架構(gòu)、易于測(cè)試一點(diǎn)也不沖突
整本書(shū)都圍繞“如何讓代碼的可讀性更高”這個(gè)目標(biāo)來(lái)寫(xiě)。這也是好代碼的重要標(biāo)準(zhǔn)之一。
使用含義明確的詞，比如用download而不是get，參考以下替換方案：
send -> deliver, dispatch, announce, distribute, route find -> search, extract, locate, recoverstart -> lanuch, create, begin, open make -> create,set up, build, generate, compose, add, new
像tmp和retval這樣詞，除了說(shuō)明是臨時(shí)變量和返回值之外，沒(méi)有任何意義。但是給他加一些有意義的詞，就會(huì)很明確：
tmp_file = tempfile.NamedTemporaryFile() ...SaveData(tmp_file, ...)
不使用retval而使用變量真正代表的意義：
sum_squares += v[i]; // Where's the "square" that we're summing? Bug!
嵌套的for循環(huán)中,i、j也有同樣讓人困惑的時(shí)候：
for (int i = 0; i < clubs.size(); i++) for (int j = 0; j < clubs[i].members.size(); j++) for (int k = 0; k < users.size(); k++) if (clubs[i].members[k] == users[j]) cout << "user[" << j << "] is in club[" << i << "]" << endl;
換一種寫(xiě)法就會(huì)清晰很多：
if (clubs[ci].members[mi] == users[ui]) # OK. First letters match.
所以，當(dāng)使用一些通用的詞，要有充分的理由才可以。
CanListenOnPort就比ServerCanStart好，can start比較含糊，而listen on port確切的說(shuō)明了這個(gè)方法將要做什么。
--run_locally就不如--extra_logging來(lái)的明確。
_ms，對(duì)原始字符串加_raw如果一個(gè)變量很重要，那么在名字上多加一些額外的字就會(huì)更加易讀，比如將string id; // Example: "af84ef845cd8"換成string hex_id;。
Start(int delay) --> delay → delay_secs CreateCache(int size) --> size → size_mbThrottleDownload(float limit) --> limit → max_kbps Rotate(float angle) --> angle → degrees_cw
更多例子：
password -> plaintext_password comment -> unescaped_comment html -> html_utf8 data -> data_urlenc
在比較小的作用域內(nèi)，可以使用較短的變量名，在較大的作用域內(nèi)使用的變量，最好用長(zhǎng)一點(diǎn)的名字，編輯器的自動(dòng)補(bǔ)全都可以很好的減少鍵盤(pán)輸入。對(duì)于一些縮寫(xiě)前綴，盡量選擇眾所周知的(如str)，一個(gè)判斷標(biāo)準(zhǔn)是，當(dāng)新成員加入時(shí)，是否可以無(wú)需他人幫助而明白前綴代表什么。
_、-等符號(hào)，比如對(duì)私有變量加_前綴。var x = new DatePicker(); // DatePicker() 是類(lèi)的"構(gòu)造"函數(shù)，大寫(xiě)開(kāi)始var y = pageHeight(); // pageHeight() 是一個(gè)普通函數(shù) var $all_images = $("img"); // $all_images 是jQuery對(duì)象var height = 250; // height不是 //id和class的寫(xiě)法分開(kāi)<div id="middle_column" class="main-content"> ...命名的時(shí)候可以先想一下，我要用的這個(gè)詞是否有別的含義。舉個(gè)例子：
results = Database.all_objects.filter("year <= 2011")現(xiàn)在的結(jié)果到底是包含2011年之前的呢還是不包含呢？
min、max代替limitCART_TOO_BIG_LIMIT = 10 if shopping_cart.num_items() >= CART_TOO_BIG_LIMIT: Error("Too many items in cart.") MAX_ITEMS_IN_CART = 10 if shopping_cart.num_items() > MAX_ITEMS_IN_CART: Error("Too many items in cart.")對(duì)比上例中CART_TOO_BIG_LIMIT和MAX_ITEMS_IN_CART，想想哪個(gè)更好呢？
first和last來(lái)表示閉區(qū)間print integer_range(start=2, stop=4)# Does this print [2,3] or [2,3,4] (or something else)? set.PrintKeys(first="Bart", last="Maggie")
first和last含義明確，適宜表示閉區(qū)間。
beigin和end表示前閉后開(kāi)(2,9))區(qū)間PrintEventsInRange("OCT 16 12:00am", "OCT 17 12:00am") PrintEventsInRange("OCT 16 12:00am", "OCT 16 11:59:59.9999pm")上面一種寫(xiě)法就比下面的舒服多了。
bool read_password = true;
這是一個(gè)很危險(xiǎn)的命名，到底是需要讀取密碼呢，還是密碼已經(jīng)被讀取呢，不知道，所以這個(gè)變量可以使用user_is_authenticated代替。通常，給Boolean型變量添加is、has、can、should可以讓含義更清晰，比如：
SpaceLeft() --> hasSpaceLeft()bool disable_ssl = false --> bool use_ssl = true
public class StatisticsCollector { public void addSample(double x) { ... } public double getMean() { // Iterate through all samples and return total / num_samples } ...}在這個(gè)例子中，getMean方法遍歷了所有的樣本，返回總額，所以并不是普通意義上輕量的get方法，所以應(yīng)該取名computeMean比較合適。
寫(xiě)出來(lái)漂亮的格式，充滿美感，讀起來(lái)自然也會(huì)舒服很多，對(duì)比下面兩個(gè)例子：
class StatsKeeper { public: // A class for keeping track of a series of doubles void Add(double d); // and methods for quick statistics about them private: int count; /* how many so far */ public: double Average(); private: double minimum; list<double> past_items ;double maximum;};什么是充滿美感的呢：
// A class for keeping track of a series of doubles// and methods for quick statistics about them.class StatsKeeper { public: void Add(double d); double Average(); private: list<double> past_items; int count; // how many so far double minimum; double maximum;};這段代碼需要斷行，來(lái)滿足不超過(guò)一行80個(gè)字符的要求，參數(shù)也需要注釋說(shuō)明：
public class PerformanceTester { public static final TcpConnectionSimulator wifi = new TcpConnectionSimulator( 500, /* Kbps */ 80, /* millisecs latency */ 200, /* jitter */ 1 /* packet loss % */); public static final TcpConnectionSimulator t3_fiber = new TcpConnectionSimulator( 45000, /* Kbps */ 10, /* millisecs latency */ 0, /* jitter */ 0 /* packet loss % */); public static final TcpConnectionSimulator cell = new TcpConnectionSimulator( 100, /* Kbps */ 400, /* millisecs latency */ 250, /* jitter */ 5 /* packet loss % */);}考慮到代碼的連貫性，先優(yōu)化成這樣：
public class PerformanceTester { public static final TcpConnectionSimulator wifi = new TcpConnectionSimulator( 500, /* Kbps */ 80, /* millisecs latency */ 200, /* jitter */ 1 /* packet loss % */); public static final TcpConnectionSimulator t3_fiber = new TcpConnectionSimulator( 45000, /* Kbps */ 10, /* millisecs latency */ 0, /* jitter */ 0 /* packet loss % */); public static final TcpConnectionSimulator cell = new TcpConnectionSimulator( 100, /* Kbps */ 400, /* millisecs latency */ 250, /* jitter */ 5 /* packet loss % */);}連貫性好一點(diǎn)，但還是太羅嗦，額外占用很多空間：
public class PerformanceTester { // TcpConnectionSimulator(throughput, latency, jitter, packet_loss) // [Kbps] [ms] [ms] [percent] public static final TcpConnectionSimulator wifi = new TcpConnectionSimulator(500, 80, 200, 1); public static final TcpConnectionSimulator t3_fiber = new TcpConnectionSimulator(45000, 10, 0, 0); public static final TcpConnectionSimulator cell = new TcpConnectionSimulator(100, 400, 250, 5);}// Turn a partial_name like "Doug Adams" into "Mr. Douglas Adams".// If not possible, 'error' is filled with an explanation.string ExpandFullName(DatabaseConnection dc, string partial_name, string* error); DatabaseConnection database_connection;string error;assert(ExpandFullName(database_connection, "Doug Adams", &error) == "Mr. Douglas Adams");assert(error == "");assert(ExpandFullName(database_connection, " Jake Brown ", &error) == "Mr. Jacob Brown III");assert(error == "");assert(ExpandFullName(database_connection, "No Such Guy", &error) == "");assert(error == "no match found");assert(ExpandFullName(database_connection, "John", &error) == "");assert(error == "more than one result");
上面這段代碼看起來(lái)很臟亂，很多重復(fù)性的東西，可以用函數(shù)封裝：
CheckFullName("Doug Adams", "Mr. Douglas Adams", "");CheckFullName(" Jake Brown ", "Mr. Jake Brown III", "");CheckFullName("No Such Guy", "", "no match found");CheckFullName("John", "", "more than one result"); void CheckFullName(string partial_name, string expected_full_name, string expected_error) { // database_connection is now a class member string error; string full_name = ExpandFullName(database_connection, partial_name, &error); assert(error == expected_error); assert(full_name == expected_full_name);}列對(duì)齊可以讓代碼段看起來(lái)更舒適：
CheckFullName("Doug Adams" , "Mr. Douglas Adams" , "");CheckFullName(" Jake Brown ", "Mr. Jake Brown III", "");CheckFullName("No Such Guy" , "" , "no match found");CheckFullName("John" , "" , "more than one result"); commands[] = { ... { "timeout" , NULL , cmd_spec_timeout}, { "timestamping" , &opt.timestamping , cmd_boolean}, { "tries" , &opt.ntry , cmd_number_inf}, { "useproxy" , &opt.use_proxy , cmd_boolean}, { "useragent" , NULL , cmd_spec_useragent}, ...};class FrontendServer { public: FrontendServer(); void ViewProfile(HttpRequest* request); void OpenDatabase(string location, string user); void SaveProfile(HttpRequest* request); string ExtractQueryParam(HttpRequest* request, string param); void ReplyOK(HttpRequest* request, string html); void FindFriends(HttpRequest* request); void ReplyNotFound(HttpRequest* request, string error); void CloseDatabase(string location); ~FrontendServer();};上面這一段雖然能看，不過(guò)還有優(yōu)化空間：
class FrontendServer { public: FrontendServer(); ~FrontendServer(); // Handlers void ViewProfile(HttpRequest* request); void SaveProfile(HttpRequest* request); void FindFriends(HttpRequest* request); // Request/Reply Utilities string ExtractQueryParam(HttpRequest* request, string param); void ReplyOK(HttpRequest* request, string html); void ReplyNotFound(HttpRequest* request, string error); // Database Helpers void OpenDatabase(string location, string user); void CloseDatabase(string location);};再來(lái)看一段代碼：
# Import the user's email contacts, and match them to users in our system.# Then display a list of those users that he/she isn't already friends with.def suggest_new_friends(user, email_password): friends = user.friends() friend_emails = set(f.email for f in friends) contacts = import_contacts(user.email, email_password) contact_emails = set(c.email for c in contacts) non_friend_emails = contact_emails - friend_emails suggested_friends = User.objects.select(email__in=non_friend_emails) display['user'] = user display['friends'] = friends display['suggested_friends'] = suggested_friends return render("suggested_friends.html", display)全都混在一起，視覺(jué)壓力相當(dāng)大，按功能化塊：
def suggest_new_friends(user, email_password): # Get the user's friends' email addresses. friends = user.friends() friend_emails = set(f.email for f in friends) # Import all email addresses from this user's email account. contacts = import_contacts(user.email, email_password) contact_emails = set(c.email for c in contacts) # Find matching users that they aren't already friends with. non_friend_emails = contact_emails - friend_emails suggested_friends = User.objects.select(email__in=non_friend_emails) # Display these lists on the page. display['user'] = user display['friends'] = friends display['suggested_friends'] = suggested_friends return render("suggested_friends.html", display)讓代碼看起來(lái)更舒服，需要在寫(xiě)的過(guò)程中多注意，培養(yǎng)一些好的習(xí)慣，尤其當(dāng)團(tuán)隊(duì)合作的時(shí)候，代碼風(fēng)格比如大括號(hào)的位置并沒(méi)有對(duì)錯(cuò)，但是不遵循團(tuán)隊(duì)規(guī)范那就是錯(cuò)的。
當(dāng)你寫(xiě)代碼的時(shí)候，你會(huì)思考很多，但是最終呈現(xiàn)給讀者的就只剩代碼本身了，額外的信息丟失了，所以注釋的目的就是讓讀者了解更多的信息。
這樣的注釋毫無(wú)價(jià)值：
// The class definition for Accountclass Account { public: // Constructor Account(); // Set the profit member to a new value void SetProfit(double profit); // Return the profit from this Account double GetProfit();};// Find a Node with the given 'name' or return NULL.// If depth <= 0, only 'subtree' is inspected.// If depth == N, only 'subtree' and N levels below are inspected.Node* FindNodeInSubtree(Node* subtree, string name, int depth);
// Enforce limits on the Reply as stated in the Request,// such as the number of items returned, or total byte size, etc. void CleanReply(Request request, Reply reply);
注釋的大部分都在解釋clean是什么意思，那不如換個(gè)正確的名字：
// Make sure 'reply' meets the count/byte/etc. limits from the 'request' void EnforceLimitsFromRequest(Request request, Reply reply);
我們討論了不該注釋什么，那么應(yīng)該注釋什么呢？注釋?xiě)?yīng)該記錄你思考代碼怎么寫(xiě)的結(jié)果，比如像下面這些：
// Surprisingly, a binary tree was 40% faster than a hash table for this data.// The cost of computing a hash was more than the left/right comparisons. // This heuristic might miss a few words. That's OK; solving this 100% is hard. // This class is getting messy. Maybe we should create a 'ResourceNode' subclass to// help organize things.
也可以用來(lái)記錄流程和常量：
// TODO: use a faster algorithm// TODO(dustin): handle other image formats besides JPEG NUM_THREADS = 8 # as long as it's >= 2 * num_processors, that's good enough. // Impose a reasonable limit - no human can read that much anyway.const int MAX_RSS_SUBSCRIPTIONS = 1000;
可用的詞有：
TODO : Stuff I haven't gotten around to yetFIXME : Known-broken code hereHACK : Adimittedly inelegant solution to a problemXXX : Danger! Major problem here
當(dāng)別人讀你的代碼時(shí)，讓他們產(chǎn)生疑問(wèn)的部分，就是你應(yīng)該注釋的地方。
struct Recorder { vector<float> data; ... void Clear() { vector<float>().swap(data); // Huh? Why not just data.clear()? }};很多C++的程序員啊看到這里，可能會(huì)想為什么不用data.clear()來(lái)代替vector.swap，所以那個(gè)地方應(yīng)該加上注釋?zhuān)?/p>
// Force vector to relinquish its memory (look up "STL swap trick")vector<float>().swap(data);
你在寫(xiě)代碼的過(guò)程中，可能用到一些hack，或者有其他需要讀代碼的人知道的陷阱，這時(shí)候就應(yīng)該注釋?zhuān)?/p>
void SendEmail(string to, string subject, string body);
而實(shí)際上這個(gè)發(fā)送郵件的函數(shù)是調(diào)用別的服務(wù)，有超時(shí)設(shè)置，所以需要注釋?zhuān)?/p>
// Calls an external service to deliver email. (Times out after 1 minute.)void SendEmail(string to, string subject, string body);
有時(shí)候?yàn)榱烁宄f(shuō)明，需要給整個(gè)文件加注釋?zhuān)屪x者有個(gè)總體的概念：
// This file contains helper functions that provide a more convenient interface to our// file system. It handles file permissions and other nitty-gritty details.
即使是在函數(shù)內(nèi)部，也可以有類(lèi)似文件注釋那樣的說(shuō)明注釋?zhuān)?/p>
# Find all the items that customers purchased for themselves.for customer_id in all_customers: for sale in all_sales[customer_id].sales: if sale.recipient == customer_id: ...
或者按照函數(shù)的步進(jìn)，寫(xiě)一些注釋?zhuān)?/p>
def GenerateUserReport(): # Acquire a lock for this user ... # Read user's info from the database ... # Write info to a file ... # Release the lock for this user
很多人不愿意寫(xiě)注釋?zhuān)_實(shí)，要寫(xiě)好注釋也不是一件簡(jiǎn)單的事情，也可以在文件專(zhuān)門(mén)的地方，留個(gè)寫(xiě)注釋的區(qū)域，可以寫(xiě)下你任何想說(shuō)的東西。
前一個(gè)小節(jié)討論了注釋?xiě)?yīng)該寫(xiě)什么，這一節(jié)來(lái)討論應(yīng)該怎么寫(xiě)，因?yàn)樽⑨尯苤匾?，所以要?xiě)的精確，注釋也占據(jù)屏幕空間，所以要簡(jiǎn)潔。
// The int is the CategoryType.// The first float in the inner pair is the 'score',// the second is the 'weight'.typedef hash_map<int, pair<float, float> > ScoreMap;
這樣寫(xiě)太羅嗦了，盡量精簡(jiǎn)壓縮成這樣：
// CategoryType -> (score, weight)typedef hash_map<int, pair<float, float> > ScoreMap;
// Insert the data into the cache, but check if it's too big first.
這里的it's有歧義，不知道所指的是data還是cache，改成如下：
// Insert the data into the cache, but check if the data is too big first.
還有更好的解決辦法，這里的it就有明確所指：
// If the data is small enough, insert it into the cache.
# Depending on whether we've already crawled this URL before, give it a different priority.
這句話理解起來(lái)太費(fèi)勁，改成如下就好理解很多：
# Give higher priority to URLs we've never crawled before.
// Return the number of lines in this file.int CountLines(string filename) { ... }這樣的一個(gè)函數(shù)，用起來(lái)可能會(huì)一頭霧水，因?yàn)樗梢杂泻芏嗥缌x：
”” 一個(gè)空文件，是0行還是1行？
“hello” 只有一行，那么返回值是0還是1？
“hello\n” 這種情況返回1還是2？
“hello\n world” 返回1還是2？
“hello\n\r cruel\n world\r” 返回2、3、4哪一個(gè)呢？
所以注釋?xiě)?yīng)該這樣寫(xiě)：
// Count how many newline bytes ('\n') are in the file.int CountLines(string filename) { ... }// Rearrange 'v' so that elements < pivot come before those >= pivot;// Then return the largest 'i' for which v[i] < pivot (or -1 if none are < pivot)int Partition(vector<int>* v, int pivot);
這個(gè)描述很精確，但是如果再加入一個(gè)例子，就更好了：
// ...// Example: Partition([8 5 9 8 2], 8) might result in [5 2 | 8 9 8] and return 1int Partition(vector<int>* v, int pivot);
void DisplayProducts(list<Product> products) { products.sort(CompareProductByPrice); // Iterate through the list in reverse order for (list<Product>::reverse_iterator it = products.rbegin(); it != products.rend(); ++it) DisplayPrice(it->price); ... }這里的注釋說(shuō)明了倒序排列，單還不夠準(zhǔn)確，應(yīng)該改成這樣：
// Display each price, from highest to lowestfor (list<Product>::reverse_iterator it = products.rbegin(); ... )
看見(jiàn)這樣的一個(gè)函數(shù)調(diào)用，肯定會(huì)一頭霧水：
Connect(10, false);
如果加上這樣的注釋?zhuān)x起來(lái)就清楚多了：
def Connect(timeout, use_encryption): ... # Call the function using named parametersConnect(timeout = 10, use_encryption = False)
// This class contains a number of members that store the same information as in the// database, but are stored here for speed. When this class is read from later, those// members are checked first to see if they exist, and if so are returned; otherwise the// database is read from and that data stored in those fields for next time.
上面這一大段注釋?zhuān)忉尩暮芮宄?，如果換一個(gè)詞來(lái)代替，也不會(huì)有什么疑惑：
// This class acts as a caching layer to the database.
讓條件語(yǔ)句、循環(huán)以及其他控制流程的代碼盡可能自然，讓讀者在閱讀過(guò)程中不需要停頓思考或者在回頭查找，是這一節(jié)的目的。
對(duì)比下面兩種條件的寫(xiě)法：
if (length >= 10)while (bytes_received < bytes_expected) if (10 <= length)while (bytes_expected > bytes_received)
到底是應(yīng)該按照大于小于的順序來(lái)呢，還是有其他的準(zhǔn)則？是的，應(yīng)該按照參數(shù)的意義來(lái)
運(yùn)算符左邊：通常是需要被檢查的變量，也就是會(huì)經(jīng)常變化的
運(yùn)算符右邊：通常是被比對(duì)的樣本，一定程度上的常量
這就解釋了為什么bytes_received < bytes_expected比反過(guò)來(lái)更好理解。
通常，if/else的順序你可以自由選擇，下面這兩種都可以：
if (a == b) { // Case One ...} else { // Case Two ...} if (a != b) { // Case Two ...} else { // Case One ...}或許對(duì)此你也沒(méi)有仔細(xì)斟酌過(guò)，但在有些時(shí)候，一種順序確實(shí)好過(guò)另一種：
正向的邏輯在前，比如if(debug)就比if(!debug)好
簡(jiǎn)單邏輯的在前，這樣if和else就可以在一個(gè)屏幕顯示 - 有趣、清晰的邏輯在前
舉個(gè)例子來(lái)看：
if (!url.HasQueryParameter("expand_all")) { response.Render(items); ...} else { for (int i = 0; i < items.size(); i++) { items[i].Expand(); } ... }看到if你首先想到的是expand_all，就好像告訴你“不要想大象”，你會(huì)忍不住去想它，所以產(chǎn)生了一點(diǎn)點(diǎn)迷惑，最好寫(xiě)成：
if (url.HasQueryParameter("expand_all")) { for (int i = 0; i < items.size(); i++) { items[i].Expand(); } ... } else { response.Render(items); ... }time_str += (hour >= 12) ? "pm" : "am"; Avoiding the ternary operator, you might write: if (hour >= 12) { time_str += "pm"; } else { time_str += "am";}使用三目運(yùn)算符可以減少代碼行數(shù)，上例就是一個(gè)很好的例證，但是我們的真正目的是減少讀代碼的時(shí)間，所以下面的情況并不適合用三目運(yùn)算符：
return exponent >= 0 ? mantissa * (1 << exponent) : mantissa / (1 << -exponent); if (exponent >= 0) { return mantissa * (1 << exponent);} else { return mantissa / (1 << -exponent);}所以只在簡(jiǎn)單表達(dá)式的地方用。
do { continue;} while (false);這段代碼會(huì)執(zhí)行幾遍呢，需要時(shí)間思考一下，do/while完全可以用別的方法代替，所以應(yīng)避免使用。
public boolean Contains(String str, String substr) { if (str == null || substr == null) return false; if (substr.equals("")) return true; ...}函數(shù)里面盡早的return，可以讓邏輯更加清晰。
if (user_result == SUCCESS) { if (permission_result != SUCCESS) { reply.WriteErrors("error reading permissions"); reply.Done(); return; } reply.WriteErrors("");} else { reply.WriteErrors(user_result);}reply.Done();這樣一段代碼，有一層的嵌套，但是看起來(lái)也會(huì)稍有迷惑，想想自己的代碼，有沒(méi)有類(lèi)似的情況呢？可以換個(gè)思路去考慮這段代碼，并且用盡早return的原則修改，看起來(lái)就舒服很多：
if (user_result != SUCCESS) { reply.WriteErrors(user_result); reply.Done(); return;}if (permission_result != SUCCESS) { reply.WriteErrors(permission_result); reply.Done(); return;}reply.WriteErrors("");reply.Done();同樣的，對(duì)于有嵌套的循環(huán)，可以采用同樣的辦法：
for (int i = 0; i < results.size(); i++) { if (results[i] != NULL) { non_null_count++; if (results[i]->name != "") { cout << "Considering candidate..." << endl; ... } }}換一種寫(xiě)法，盡早return，在循環(huán)中就用continue：
for (int i = 0; i < results.size(); i++) { if (results[i] == NULL) continue; non_null_count++; if (results[i]->name == "") continue; cout << "Considering candidate..." << endl; ... }很顯然的，越復(fù)雜的表達(dá)式，讀起來(lái)越費(fèi)勁，所以應(yīng)該把那些復(fù)雜而龐大的表達(dá)式，拆分成一個(gè)個(gè)易于理解的小式子。
將復(fù)雜表達(dá)式拆分最簡(jiǎn)單的辦法，就是增加一個(gè)變量：
if line.split(':')[0].strip() == "root": //用變量替換username = line.split(':')[0].strip() if username == "root": ...或者這個(gè)例子：
if (request.user.id == document.owner_id) { // user can edit this document...}...if (request.user.id != document.owner_id) {// document is read-only...} //用變量替換final boolean user_owns_document = (request.user.id == document.owner_id);if (user_owns_document) { // user can edit this document...}...if (!user_owns_document) { // document is read-only...}1) not (a or b or c) <–> (not a) and (not b) and (not c)
2) not (a and b and c) <–> (not a) or (not b) or (not c)
所以，就可以這樣寫(xiě)：
if (!(file_exists && !is_protected)) Error("Sorry, could not read file."); //替換if (!file_exists || is_protected) Error("Sorry, could not read file.");assert((!(bucket = FindBucket(key))) || !bucket->IsOccupied());
這樣的代碼完全可以用下面這個(gè)替換，雖然有兩行，但是更易懂：
bucket = FindBucket(key);if (bucket != NULL) assert(!bucket->IsOccupied());
像下面這樣的表達(dá)式，最好也不要寫(xiě)，因?yàn)樵谟行┱Z(yǔ)言中，x會(huì)被賦予第一個(gè)為true的變量的值：
x = a || b || c
var update_highlight = function (message_num) { if ($("#vote_value" + message_num).html() === "Up") { $("#thumbs_up" + message_num).addClass("highlighted"); $("#thumbs_down" + message_num).removeClass("highlighted"); } else if ($("#vote_value" + message_num).html() === "Down") { $("#thumbs_up" + message_num).removeClass("highlighted"); $("#thumbs_down" + message_num).addClass("highlighted"); } else { $("#thumbs_up" + message_num).removeClass("highighted"); $("#thumbs_down" + message_num).removeClass("highlighted"); }};這里面有很多重復(fù)的語(yǔ)句，我們可以用變量還替換簡(jiǎn)化：
var update_highlight = function (message_num) { var thumbs_up = $("#thumbs_up" + message_num); var thumbs_down = $("#thumbs_down" + message_num); var vote_value = $("#vote_value" + message_num).html(); var hi = "highlighted"; if (vote_value === "Up") { thumbs_up.addClass(hi); thumbs_down.removeClass(hi); } else if (vote_value === "Down") { thumbs_up.removeClass(hi); thumbs_down.addClass(hi); } else { thumbs_up.removeClass(hi); thumbs_down.removeClass(hi); }}前一節(jié)，講到利用變量來(lái)拆解大表達(dá)式，這一節(jié)來(lái)討論如何消除多余的變量。
now = datetime.datetime.now()root_message.last_view_time = now
這里的now可以去掉，因?yàn)椋?/p>
并非用來(lái)拆分復(fù)雜的表達(dá)式
也沒(méi)有增加可讀性，因?yàn)閌datetime.datetime.now()`本就清晰
只用了一次
所以完全可以寫(xiě)作：
root_message.last_view_time = datetime.datetime.now()
boolean done = false;while (/* condition */ && !done) { ... if (...) { done = true; continue; }}這里的done可以用別的方式更好的完成：
while (/* condition */) { ... if (...) { break; } }這個(gè)例子非常容易修改，如果是比較復(fù)雜的嵌套，break可能并不夠用，這時(shí)候就可以把代碼封裝到函數(shù)中。
我們都聽(tīng)過(guò)要避免使用全局變量這樣的忠告，是的，當(dāng)變量的作用域越大，就越難追蹤，所以要保持變量小的作用域。
class LargeClass { string str_; void Method1() { str_ = ...; Method2(); } void Method2() { // Uses str_ } // Lots of other methods that don't use str_ ... ;}這里的str_的作用域有些大，完全可以換一種方式：
class LargeClass { void Method1() { string str = ...; Method2(str); } void Method2(string str) { // Uses str } // Now other methods can't see str.};將str通過(guò)變量函數(shù)參數(shù)傳遞，減小了作用域，也更易讀。同樣的道理也可以用在定義類(lèi)的時(shí)候，將大類(lèi)拆分成一個(gè)個(gè)小類(lèi)。
# No use of example_value up to this point.if request: for value in request.values: if value > 0: example_value = value break for logger in debug.loggers: logger.log("Example:", example_value)這個(gè)例子在運(yùn)行時(shí)候會(huì)報(bào)example_value is undefined的錯(cuò)，修改起來(lái)不算難：
example_value = Noneif request: for value in request.values: if value > 0: example_value = value break if example_value: for logger in debug.loggers: logger.log("Example:", example_value)但是參考前面的消除中間變量準(zhǔn)則，還有更好的辦法：
def LogExample(value): for logger in debug.loggers: logger.log("Example:", value) if request: for value in request.values: if value > 0: LogExample(value) # deal with 'value' immediately break在C語(yǔ)言中，要求將所有的變量事先聲明，這樣當(dāng)用到變量較多時(shí)候，讀者處理這些信息就會(huì)有難度，所以一開(kāi)始沒(méi)用到的變量，就暫緩聲明：
def ViewFilteredReplies(original_id): filtered_replies = [] root_message = Messages.objects.get(original_id) all_replies = Messages.objects.select(root_id=original_id) root_message.view_count += 1 root_message.last_view_time = datetime.datetime.now() root_message.save() for reply in all_replies: if reply.spam_votes <= MAX_SPAM_VOTES: filtered_replies.append(reply) return filtered_replies
讀者一次處理變量太多，可以暫緩聲明：
def ViewFilteredReplies(original_id): root_message = Messages.objects.get(original_id) root_message.view_count += 1 root_message.last_view_time = datetime.datetime.now() root_message.save() all_replies = Messages.objects.select(root_id=original_id) filtered_replies = [] for reply in all_replies: if reply.spam_votes <= MAX_SPAM_VOTES: filtered_replies.append(reply) return filtered_replies
前面討論了過(guò)多的變量會(huì)讓讀者迷惑，同一個(gè)變量，不停的被賦值也會(huì)讓讀者頭暈，如果變量變化的次數(shù)少一些，代碼可讀性就更強(qiáng)。
假設(shè)有一個(gè)頁(yè)面，如下，需要給第一個(gè)空的input賦值：
<input type="text" id="input1" value="Dustin"><input type="text" id="input2" value="Trevor"><input type="text" id="input3" value=""><input type="text" id="input4" value="Melissa">...var setFirstEmptyInput = function (new_value) { var found = false; var i = 1; var elem = document.getElementById('input' + i); while (elem !== null) { if (elem.value === '') { found = true; break; } i++; elem = document.getElementById('input' + i); } if (found) elem.value = new_value; return elem;};這段代碼能工作，有三個(gè)變量，我們逐一去看如何優(yōu)化，found作為中間變量，完全可以消除：
var setFirstEmptyInput = function (new_value) { var i = 1; var elem = document.getElementById('input' + i); while (elem !== null) { if (elem.value === '') { elem.value = new_value; return elem; } i++; elem = document.getElementById('input' + i); } return null;};再來(lái)看elem變量，只用來(lái)做循環(huán)，調(diào)用了很多次，所以很難跟蹤他的值，i也可以用for來(lái)修改：
var setFirstEmptyInput = function (new_value) { for (var i = 1; true; i++) { var elem = document.getElementById('input' + i); if (elem === null) return null; // Search Failed. No empty input found. if (elem.value === '') { elem.value = new_value; return elem; } }};工程師就是將大問(wèn)題分解為一個(gè)個(gè)小問(wèn)題，然后逐個(gè)解決，這樣也易于保證程序的健壯性、可讀性。如何分解子問(wèn)題，下面給出一些準(zhǔn)則：
看看這個(gè)方法或代碼，問(wèn)問(wèn)你自己“這段代碼的最終目標(biāo)是什么？”
對(duì)于每一行代碼，要問(wèn)“它與目標(biāo)直接相關(guān)，或者是不相關(guān)的子問(wèn)題？”
如果有足夠多行的代碼是處理與目標(biāo)不直接相關(guān)的問(wèn)題，那么抽離成子函數(shù)
來(lái)看一個(gè)例子：
ajax_post({ url: 'http://example.com/submit', data: data, on_success: function (response_data) { var str = "{\n"; for (var key in response_data) { str += " " + key + " = " + response_data[key] + "\n"; } alert(str + "}"); // Continue handling 'response_data' ... }});這段代碼的目標(biāo)是發(fā)送一個(gè)ajax請(qǐng)求，所以其中字符串處理的部分就可以抽離出來(lái)：
var format_pretty = function (obj) { var str = "{\n"; for (var key in obj) { str += " " + key + " = " + obj[key] + "\n"; } return str + "}";};有很多理由將format_pretty抽離出來(lái)，這些獨(dú)立的函數(shù)可以很容易的添加feature，增強(qiáng)可靠性，處理邊界情況，等等。所以這里，可以將format_pretty增強(qiáng)，就會(huì)得到一個(gè)更強(qiáng)大的函數(shù)：
var format_pretty = function (obj, indent) { // Handle null, undefined, strings, and non-objects. if (obj === null) return "null"; if (obj === undefined) return "undefined"; if (typeof obj === "string") return '"' + obj + '"'; if (typeof obj !== "object") return String(obj); if (indent === undefined) indent = ""; // Handle (non-null) objects. var str = "{\n"; for (var key in obj) { str += indent + " " + key + " = "; str += format_pretty(obj[key], indent + " ") + "\n"; } return str + indent + "}";};這個(gè)函數(shù)輸出：
{ key1 = 1 key2 = true key3 = undefined key4 = null key5 = { key5a = { key5a1 = "hello world" } }}多做這樣的事情，就是積累代碼的過(guò)程，這樣的代碼可以復(fù)用，也可以形成自己的代碼庫(kù)，或者分享給別人。
那些與目標(biāo)不相關(guān)函數(shù)，抽離出來(lái)可以復(fù)用，與業(yè)務(wù)相關(guān)的也可以抽出來(lái)，保持代碼的易讀性，例如：
business = Business()business.name = request.POST["name"] url_path_name = business.name.lower()url_path_name = re.sub(r"['\.]", "", url_path_name) url_path_name = re.sub(r"[^a-z0-9]+", "-", url_path_name) url_path_name = url_path_name.strip("-")business.url = "/biz/" + url_path_name business.date_created = datetime.datetime.utcnow() business.save_to_database()抽離出來(lái)，就好看很多：
CHARS_TO_REMOVE = re.compile(r"['\.']+")CHARS_TO_DASH = re.compile(r"[^a-z0-9]+") def make_url_friendly(text): text = text.lower() text = CHARS_TO_REMOVE.sub('', text) text = CHARS_TO_DASH.sub('-', text) return text.strip("-") business = Business()business.name = request.POST["name"]business.url = "/biz/" + make_url_friendly(business.name) business.date_created = datetime.datetime.utcnow() business.save_to_database()我們來(lái)看一個(gè)讀寫(xiě)cookie的函數(shù)：
var max_results;var cookies = document.cookie.split(';');for (var i = 0; i < cookies.length; i++) { var c = cookies[i]; c = c.replace(/^[ ]+/, ''); // remove leading spaces if (c.indexOf("max_results=") === 0) max_results = Number(c.substring(12, c.length));}這段代碼實(shí)在太丑了，理想的接口應(yīng)該是這樣的：
set_cookie(name, value, days_to_expire);delete_cookie(name);
對(duì)于并不理想的接口，你永遠(yuǎn)可以用自己的函數(shù)做封裝，讓接口更好用。
ser_info = { "username": "...", "password": "..." }user_str = json.dumps(user_info)cipher = Cipher("aes_128_cbc", key=PRIVATE_KEY, init_vector=INIT_VECTOR, op=ENCODE)encrypted_bytes = cipher.update(user_str)encrypted_bytes += cipher.final() # flush out the current 128 bit blockurl = "http://example.com/?user_info=" + base64.urlsafe_b64encode(encrypted_bytes)...雖然終極目的是拼接用戶信息的字符，但是代碼大部分做的事情是解析python的object，所以：
def url_safe_encrypt(obj): obj_str = json.dumps(obj) cipher = Cipher("aes_128_cbc", key=PRIVATE_KEY, init_vector=INIT_VECTOR, op=ENCODE) encrypted_bytes = cipher.update(obj_str) encrypted_bytes += cipher.final() # flush out the current 128 bit block return base64.urlsafe_b64encode(encrypted_bytes)這樣在其他地方也可以調(diào)用：
user_info = { "username": "...", "password": "..." }url = "http://example.com/?user_info=" + url_safe_encrypt(user_info)分離子函數(shù)是好習(xí)慣，但是也要適度，過(guò)度的分離成多個(gè)小函數(shù)，也會(huì)讓查找變得困難。
代碼應(yīng)該是一次只完成一個(gè)任務(wù)
var place = location_info["LocalityName"]; // e.g. "Santa Monica"if (!place) { place = location_info["SubAdministrativeAreaName"]; // e.g. "Los Angeles"}if (!place) { place = location_info["AdministrativeAreaName"]; // e.g. "California"}if (!place) { place = "Middle-of-Nowhere";}if (location_info["CountryName"]) { place += ", " + location_info["CountryName"]; // e.g. "USA"} else { place += ", Planet Earth";} return place;這是一個(gè)用來(lái)拼地名的函數(shù)，有很多的條件判斷，讀起來(lái)非常吃力，有沒(méi)有辦法拆解任務(wù)呢？
var town = location_info["LocalityName"]; // e.g. "Santa Monica"var city = location_info["SubAdministrativeAreaName"]; // e.g. "Los Angeles"var state = location_info["AdministrativeAreaName"]; // e.g. "CA"var country = location_info["CountryName"]; // e.g. "USA"
先拆解第一個(gè)任務(wù)，將各變量分別保存，這樣在后面使用中不需要去記憶那些繁長(zhǎng)的key值了，第二個(gè)任務(wù)，解決地址拼接的后半部分：
// Start with the default, and keep overwriting with the most specific value. var second_half = "Planet Earth";if (country) { second_half = country; }if (state && country === "USA") { second_half = state; }再來(lái)解決前半部分：
var first_half = "Middle-of-Nowhere";if (state && country !== "USA") { first_half = state; }if (city) { first_half = city;}if (town) { first_half = town; }大功告成：
return first_half + ", " + second_half;
如果注意到有USA這個(gè)變量的判斷的話，也可以這樣寫(xiě)：
var first_half, second_half;if (country === "USA") { first_half = town || city || "Middle-of-Nowhere"; second_half = state || "USA";} else { first_half = town || city || state || "Middle-of-Nowhere"; second_half = country || "Planet Earth";}return first_half + ", " + second_half;要把一個(gè)復(fù)雜的東西解釋給別人，一些細(xì)節(jié)很容易就讓人產(chǎn)生迷惑，所以想象把你的代碼用平實(shí)的語(yǔ)言解釋給別人聽(tīng)，別人是否能懂，有一些準(zhǔn)則可以幫助你讓代碼更清晰：
用最平實(shí)的語(yǔ)言描述代碼的目的，就像給讀者講述一樣
注意描述中關(guān)鍵的字詞
讓你的代碼符合你的描述
下面這段代碼用來(lái)校驗(yàn)用戶的權(quán)限：
$is_admin = is_admin_request();if ($document) { if (!$is_admin && ($document['username'] != $_SESSION['username'])) { return not_authorized(); }} else { if (!$is_admin) { return not_authorized(); } }// continue rendering the page ...這一段代碼不長(zhǎng)，里面的邏輯嵌套倒是復(fù)雜，參考前面章節(jié)所述，嵌套太多非常影響閱讀理解，將這個(gè)邏輯用語(yǔ)言描述就是：
有兩種情況有權(quán)限：1、你是管理員(admin)2、你擁有這個(gè)文檔否則就沒(méi)有權(quán)限
根據(jù)描述來(lái)寫(xiě)代碼：
if (is_admin_request()) { // authorized} elseif ($document && ($document['username'] == $_SESSION['username'])) { // authorized} else { return not_authorized();}// continue rendering the page ...以上就是“web開(kāi)發(fā)中怎么編寫(xiě)可讀代碼”這篇文章的所有內(nèi)容，感謝各位的閱讀！相信大家閱讀完這篇文章都有很大的收獲，小編每天都會(huì)為大家更新不同的知識(shí)，如果還想學(xué)習(xí)更多的知識(shí)，請(qǐng)關(guān)注億速云行業(yè)資訊頻道。
免責(zé)聲明：本站發(fā)布的內(nèi)容（圖片、視頻和文字）以原創(chuàng)、轉(zhuǎn)載和分享為主，文章觀點(diǎn)不代表本網(wǎng)站立場(chǎng)，如果涉及侵權(quán)請(qǐng)聯(lián)系站長(zhǎng)郵箱：is@yisu.com進(jìn)行舉報(bào)，并提供相關(guān)證據(jù)，一經(jīng)查實(shí)，將立刻刪除涉嫌侵權(quán)內(nèi)容。
億速云公眾號(hào)
手機(jī)網(wǎng)站二維碼