web开发中怎么编写可读代码
今天小编给大家分享一下web开发中怎么编写可读代码的相关知识点,内容详细,逻辑清晰,相信大部分人都还太了解这方面的知识,所以分享这篇文章给大家参考一下,希望大家阅读完这篇文章后有所收获,下面我们一起来了解一下吧。
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代码为什么要易于理解
“Code should be written to minimize the time it would take for someone else to understand it.”
日常工作的事实是:
写代码前的思考和看代码的时间远大于真正写的时间
读代码是很平常的事情,不论是别人的,还是自己的,半年前写的可认为是别人的代码
代码可读性高,很快就可以理解程序的逻辑,进入工作状态
行数少的代码不一定就容易理解
代码的可读性与程序的效率、架构、易于测试一点也不冲突
整本书都围绕“如何让代码的可读性更高”这个目标来写。这也是好代码的重要标准之一。
如何命名
变量名中应包含更多信息
使用含义明确的词,比如用download而不是get,参考以下替换方案:
send -> deliver, dispatch, announce, distribute, route find -> search, extract, locate, recoverstart -> lanuch, create, begin, open make -> create,set up, build, generate, compose, add, new
避免通用的词
像tmp
和retval
这样词,除了说明是临时变量和返回值之外,没有任何意义。但是给他加一些有意义的词,就会很明确:
tmp_file = tempfile.NamedTemporaryFile() ...SaveData(tmp_file, ...)
不使用retval而使用变量真正代表的意义:
sum_squares += v[i]; // Where's the "square" that we're summing? Bug!
嵌套的for循环中,i
、j
也有同样让人困惑的时候:
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;
换一种写法就会清晰很多:
if (clubs[ci].members[mi] == users[ui]) # OK. First letters match.
所以,当使用一些通用的词,要有充分的理由才可以。
使用具体的名字
CanListenOnPort
就比ServerCanStart
好,can start比较含糊,而listen on port确切的说明了这个方法将要做什么。
--run_locally
就不如--extra_logging
来的明确。
增加重要的细节,比如变量的单位_ms
,对原始字符串加_raw
如果一个变量很重要,那么在名字上多加一些额外的字就会更加易读,比如将string id; // Example: "af84ef845cd8"
换成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
对于作用域大的变量使用较长的名字
在比较小的作用域内,可以使用较短的变量名,在较大的作用域内使用的变量,最好用长一点的名字,编辑器的自动补全都可以很好的减少键盘输入。对于一些缩写前缀,尽量选择众所周知的(如str),一个判断标准是,当新成员加入时,是否可以无需他人帮助而明白前缀代表什么。
合理使用_
、-
等符号,比如对私有变量加_
前缀。
var x = new DatePicker(); // DatePicker() 是类的"构造"函数,大写开始var y = pageHeight(); // pageHeight() 是一个普通函数 var $all_images = $("img"); // $all_images 是jQuery对象var height = 250; // height不是 //id和class的写法分开...命名不能有歧义
命名的时候可以先想一下,我要用的这个词是否有别的含义。举个例子:
results = Database.all_objects.filter("year <= 2011")现在的结果到底是包含2011年之前的呢还是不包含呢?
使用
min
、max
代替limit
CART_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.")对比上例中
CART_TOO_BIG_LIMIT
和MAX_ITEMS_IN_CART
,想想哪个更好呢?使用
first
和last
来表示闭区间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
含义明确,适宜表示闭区间。使用
beigin
和end
表示前闭后开(2,9))区间PrintEventsInRange("OCT 16 12:00am", "OCT 17 12:00am") PrintEventsInRange("OCT 16 12:00am", "OCT 16 11:59:59.9999pm")上面一种写法就比下面的舒服多了。
Boolean型变量命名
bool read_password = true;这是一个很危险的命名,到底是需要读取密码呢,还是密码已经被读取呢,不知道,所以这个变量可以使用
user_is_authenticated
代替。通常,给Boolean型变量添加is
、has
、can
、should
可以让含义更清晰,比如:SpaceLeft() --> hasSpaceLeft()bool disable_ssl = false --> bool use_ssl = true符合预期
public class StatisticsCollector { public void addSample(double x) { ... } public double getMean() { // Iterate through all samples and return total / num_samples } ...}在这个例子中,
getMean
方法遍历了所有的样本,返回总额,所以并不是普通意义上轻量的get
方法,所以应该取名computeMean
比较合适。漂亮的格式
写出来漂亮的格式,充满美感,读起来自然也会舒服很多,对比下面两个例子:
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; listpast_items ;double maximum;}; 什么是充满美感的呢:
// 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: listpast_items; int count; // how many so far double minimum; double maximum;}; 考虑断行的连续性和简洁
这段代码需要断行,来满足不超过一行80个字符的要求,参数也需要注释说明:
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 % */);}考虑到代码的连贯性,先优化成这样:
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 % */);}连贯性好一点,但还是太罗嗦,额外占用很多空间:
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);}用函数封装
// 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");上面这段代码看起来很脏乱,很多重复性的东西,可以用函数封装:
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);}列对齐
列对齐可以让代码段看起来更舒适:
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}, ...};代码用块区分
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();};上面这一段虽然能看,不过还有优化空间:
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);};再来看一段代码:
# 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,视觉压力相当大,按功能化块:
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)让代码看起来更舒服,需要在写的过程中多注意,培养一些好的习惯,尤其当团队合作的时候,代码风格比如大括号的位置并没有对错,但是不遵循团队规范那就是错的。
如何写注释
当你写代码的时候,你会思考很多,但是最终呈现给读者的就只剩代码本身了,额外的信息丢失了,所以注释的目的就是让读者了解更多的信息。
应该注释什么
不应该注释什么
这样的注释毫无价值:
// 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();};不要像下面这样为了注释而注释:
// 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);不要给烂取名注释
// 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);注释的大部分都在解释clean是什么意思,那不如换个正确的名字:
// Make sure 'reply' meets the count/byte/etc. limits from the 'request' void EnforceLimitsFromRequest(Request request, Reply reply);记录你的想法
我们讨论了不该注释什么,那么应该注释什么呢?注释应该记录你思考代码怎么写的结果,比如像下面这些:
// 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.也可以用来记录流程和常量:
// 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;可用的词有:
TODO : Stuff I haven't gotten around to yetFIXME : Known-broken code hereHACK : Adimittedly inelegant solution to a problemXXX : Danger! Major problem here站在读者的角度去思考
当别人读你的代码时,让他们产生疑问的部分,就是你应该注释的地方。
struct Recorder { vectordata; ... void Clear() { vector ().swap(data); // Huh? Why not just data.clear()? }}; 很多C++的程序员啊看到这里,可能会想为什么不用
data.clear()
来代替vector.swap
,所以那个地方应该加上注释:// Force vector to relinquish its memory (look up "STL swap trick")vector().swap(data); 说明可能陷阱
你在写代码的过程中,可能用到一些hack,或者有其他需要读代码的人知道的陷阱,这时候就应该注释:
void SendEmail(string to, string subject, string body);而实际上这个发送邮件的函数是调用别的服务,有超时设置,所以需要注释:
// Calls an external service to deliver email. (Times out after 1 minute.)void SendEmail(string to, string subject, string body);全景的注释
有时候为了更清楚说明,需要给整个文件加注释,让读者有个总体的概念:
// This file contains helper functions that provide a more convenient interface to our// file system. It handles file permissions and other nitty-gritty details.总结性的注释
即使是在函数内部,也可以有类似文件注释那样的说明注释:
# 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: ...或者按照函数的步进,写一些注释:
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很多人不愿意写注释,确实,要写好注释也不是一件简单的事情,也可以在文件专门的地方,留个写注释的区域,可以写下你任何想说的东西。
注释应简明准确
前一个小节讨论了注释应该写什么,这一节来讨论应该怎么写,因为注释很重要,所以要写的精确,注释也占据屏幕空间,所以要简洁。
精简注释
// The int is the CategoryType.// The first float in the inner pair is the 'score',// the second is the 'weight'.typedef hash_map> ScoreMap; 这样写太罗嗦了,尽量精简压缩成这样:
// CategoryType -> (score, weight)typedef hash_map> ScoreMap; 避免有歧义的代词
// Insert the data into the cache, but check if it's too big first.这里的
it's
有歧义,不知道所指的是data
还是cache
,改成如下:// Insert the data into the cache, but check if the data is too big first.还有更好的解决办法,这里的
it
就有明确所指:// If the data is small enough, insert it into the cache.语句要精简准确
# Depending on whether we've already crawled this URL before, give it a different priority.这句话理解起来太费劲,改成如下就好理解很多:
# Give higher priority to URLs we've never crawled before.精确描述函数的目的
// Return the number of lines in this file.int CountLines(string filename) { ... }这样的一个函数,用起来可能会一头雾水,因为他可以有很多歧义:
”” 一个空文件,是0行还是1行?
“hello” 只有一行,那么返回值是0还是1?
“hello\n” 这种情况返回1还是2?
“hello\n world” 返回1还是2?
“hello\n\r cruel\n world\r” 返回2、3、4哪一个呢?
所以注释应该这样写:
// Count how many newline bytes ('\n') are in the file.int CountLines(string filename) { ... }用实例说明边界情况
// 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* v, int pivot); 这个描述很精确,但是如果再加入一个例子,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* v, int pivot); 说明你的代码的真正目的
void DisplayProducts(listproducts) { products.sort(CompareProductByPrice); // Iterate through the list in reverse order for (list ::reverse_iterator it = products.rbegin(); it != products.rend(); ++it) DisplayPrice(it->price); ... } 这里的注释说明了倒序排列,单还不够准确,应该改成这样:
// Display each price, from highest to lowestfor (list::reverse_iterator it = products.rbegin(); ... ) 函数调用时的注释
看见这样的一个函数调用,肯定会一头雾水:
Connect(10, false);如果加上这样的注释,读起来就清楚多了:
def Connect(timeout, use_encryption): ... # Call the function using named parametersConnect(timeout = 10, use_encryption = False)使用信息含量丰富的词
// 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.上面这一大段注释,解释的很清楚,如果换一个词来代替,也不会有什么疑惑:
// This class acts as a caching layer to the database.简化循环和逻辑
流程控制要简单
让条件语句、循环以及其他控制流程的代码尽可能自然,让读者在阅读过程中不需要停顿思考或者在回头查找,是这一节的目的。
条件语句中参数的位置
对比下面两种条件的写法:
if (length >= 10)while (bytes_received < bytes_expected) if (10 <= length)while (bytes_expected > bytes_received)到底是应该按照大于小于的顺序来呢,还是有其他的准则?是的,应该按照参数的意义来
运算符左边:通常是需要被检查的变量,也就是会经常变化的
运算符右边:通常是被比对的样本,一定程度上的常量
这就解释了为什么
bytes_received < bytes_expected
比反过来更好理解。if/else的顺序
通常,
if/else
的顺序你可以自由选择,下面这两种都可以:if (a == b) { // Case One ...} else { // Case Two ...} if (a != b) { // Case Two ...} else { // Case One ...}或许对此你也没有仔细斟酌过,但在有些时候,一种顺序确实好过另一种:
正向的逻辑在前,比如
if(debug)
就比if(!debug)
好简单逻辑的在前,这样
if
和else
就可以在一个屏幕显示 - 有趣、清晰的逻辑在前举个例子来看:
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
,就好像告诉你“不要想大象”,你会忍不住去想它,所以产生了一点点迷惑,最好写成:if (url.HasQueryParameter("expand_all")) { for (int i = 0; i < items.size(); i++) { items[i].Expand(); } ... } else { response.Render(items); ... }三目运算符(?:)
time_str += (hour >= 12) ? "pm" : "am"; Avoiding the ternary operator, you might write: if (hour >= 12) { time_str += "pm"; } else { time_str += "am";}使用三目运算符可以减少代码行数,上例就是一个很好的例证,但是我们的真正目的是减少读代码的时间,所以下面的情况并不适合用三目运算符:
return exponent >= 0 ? mantissa * (1 << exponent) : mantissa / (1 << -exponent); if (exponent >= 0) { return mantissa * (1 << exponent);} else { return mantissa / (1 << -exponent);}所以只在简单表达式的地方用。
避免使用do/while表达式
do { continue;} while (false);这段代码会执行几遍呢,需要时间思考一下,
do/while
完全可以用别的方法代替,所以应避免使用。尽早return
public boolean Contains(String str, String substr) { if (str == null || substr == null) return false; if (substr.equals("")) return true; ...}函数里面尽早的return,可以让逻辑更加清晰。
减少嵌套
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();这样一段代码,有一层的嵌套,但是看起来也会稍有迷惑,想想自己的代码,有没有类似的情况呢?可以换个思路去考虑这段代码,并且用尽早return的原则修改,看起来就舒服很多:
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();同样的,对于有嵌套的循环,可以采用同样的办法:
for (int i = 0; i < results.size(); i++) { if (results[i] != NULL) { non_null_count++; if (results[i]->name != "") { cout << "Considering candidate..." << endl; ... } }}换一种写法,尽早return,在循环中就用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; ... }拆分复杂表达式
很显然的,越复杂的表达式,读起来越费劲,所以应该把那些复杂而庞大的表达式,拆分成一个个易于理解的小式子。
用变量
将复杂表达式拆分最简单的办法,就是增加一个变量:
if line.split(':')[0].strip() == "root": //用变量替换username = line.split(':')[0].strip() if username == "root": ...或者这个例子:
if (request.user.id == document.owner_id) { // user can edit this document...}...if (request.user.id != document.owner_id) {// document is read-only...} //用变量替换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...}逻辑替换
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,就可以这样写:
if (!(file_exists && !is_protected)) Error("Sorry, could not read file."); //替换if (!file_exists || is_protected) Error("Sorry, could not read file.");不要滥用逻辑表达式
assert((!(bucket = FindBucket(key))) || !bucket->IsOccupied());这样的代码完全可以用下面这个替换,虽然有两行,但是更易懂:
bucket = FindBucket(key);if (bucket != NULL) assert(!bucket->IsOccupied());像下面这样的表达式,最好也不要写,因为在有些语言中,x会被赋予第一个为
true
的变量的值:x = a || b || c拆解大表达式
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"); }};这里面有很多重复的语句,我们可以用变量还替换简化:
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); }}变量与可读性
消除变量
前一节,讲到利用变量来拆解大表达式,这一节来讨论如何消除多余的变量。
没用的临时变量
now = datetime.datetime.now()root_message.last_view_time = now这里的
now
可以去掉,因为:
并非用来拆分复杂的表达式
也没有增加可读性,因为`datetime.datetime.now()`本就清晰
只用了一次
所以完全可以写作:
root_message.last_view_time = datetime.datetime.now()消除条件控制变量
boolean done = false;while (/* condition */ && !done) { ... if (...) { done = true; continue; }}这里的
done
可以用别的方式更好的完成:while (/* condition */) { ... if (...) { break; } }这个例子非常容易修改,如果是比较复杂的嵌套,
break
可能并不够用,这时候就可以把代码封装到函数中。减少变量的作用域
我们都听过要避免使用全局变量这样的忠告,是的,当变量的作用域越大,就越难追踪,所以要保持变量小的作用域。
class LargeClass { string str_; void Method1() { str_ = ...; Method2(); } void Method2() { // Uses str_ } // Lots of other methods that don't use str_ ... ;}这里的
str_
的作用域有些大,完全可以换一种方式:class LargeClass { void Method1() { string str = ...; Method2(str); } void Method2(string str) { // Uses str } // Now other methods can't see str.};将
str
通过变量函数参数传递,减小了作用域,也更易读。同样的道理也可以用在定义类的时候,将大类拆分成一个个小类。不要使用嵌套的作用域
# 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)这个例子在运行时候会报
example_value is undefined
的错,修改起来不算难: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)但是参考前面的消除中间变量准则,还有更好的办法:
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用到了再声明
在C语言中,要求将所有的变量事先声明,这样当用到变量较多时候,读者处理这些信息就会有难度,所以一开始没用到的变量,就暂缓声明:
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读者一次处理变量太多,可以暂缓声明:
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变量最好只写一次
前面讨论了过多的变量会让读者迷惑,同一个变量,不停的被赋值也会让读者头晕,如果变量变化的次数少一些,代码可读性就更强。
一个例子
假设有一个页面,如下,需要给第一个空的
input
赋值:...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;};这段代码能工作,有三个变量,我们逐一去看如何优化,
found
作为中间变量,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;};再来看
elem
变量,只用来做循环,调用了很多次,所以很难跟踪他的值,i
也可以用for
来修改: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; } }};重新组织你的代码
分离不相关的子问题
工程师就是将大问题分解为一个个小问题,然后逐个解决,这样也易于保证程序的健壮性、可读性。如何分解子问题,下面给出一些准则:
看看这个方法或代码,问问你自己“这段代码的最终目标是什么?”
对于每一行代码,要问“它与目标直接相关,或者是不相关的子问题?”
如果有足够多行的代码是处理与目标不直接相关的问题,那么抽离成子函数
来看一个例子:
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' ... }});这段代码的目标是发送一个
ajax
请求,所以其中字符串处理的部分就可以抽离出来:var format_pretty = function (obj) { var str = "{\n"; for (var key in obj) { str += " " + key + " = " + obj[key] + "\n"; } return str + "}";};意外收获
有很多理由将
format_pretty
抽离出来,这些独立的函数可以很容易的添加feature,增强可靠性,处理边界情况,等等。所以这里,可以将format_pretty
增强,就会得到一个更强大的函数: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(ob
文章名称:web开发中怎么编写可读代码
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