Go coding in go way

1 .Go coding in go way GopherChina 2017 15 April 2017 Tony Bai Neusoft 

2 .人类语言与思维：萨丕尔-沃夫假说 "语言影响/决定思维" - 萨丕尔-沃夫假说 ("Language in uences/determines thought" - Sapir-Whorf hypothesis) 

3 .编程语言与思维：图灵奖得主的认知 "A language that doesn't a ect the way you think about programming is not worth knowing." - Alan J. Perlis(艾伦·佩利)，首届图灵奖得主 

4 .问题: 素数筛 素数是一个自然数，它具有两个截然不同的自然数除数：1和它本身。 要找到小于或等于给定 整数n的素数，我们可以使用Eratosthenes' sieve(埃拉托斯特尼)算法 (https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes) 。 算法描述：先用最小的素数2去筛，把2的倍数剔除掉；下一个未筛除的数就是素数(这里是3)。 再用这个素数3去筛，筛除掉3的倍数... 这样不断重复下去，直到筛完为止。 

5 .sieve.c //基于数组的内存操作 void sieve() { int c, i,j,numbers[LIMIT], primes[PRIMES]; for (i=0;i<LIMIT;i++){ numbers[i]=i+2; /*fill the array with natural numbers*/ } for (i=0;i<LIMIT;i++){ if (numbers[i]!=-1){ for (j=2*numbers[i]-2;j<LIMIT;j+=numbers[i]) numbers[j]=-1; /*sieve the non-primes*/ } } c = j = 0; for (i=0;i<LIMIT&&j<PRIMES;i++) { if (numbers[i]!=-1) { primes[j++] = numbers[i]; /*transfer the primes to their own array*/ c++; } } for (i=0;i<c;i++) printf("%d\n",primes[i]); } 

6 .sieve.hs //函数递归 sieve [] = [] sieve (x:xs) = x : sieve (filter (\a -> not $ a `mod` x == 0) xs) n = 100 main = print $ sieve [2..n] [2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97] 

7 .sieve.go //并发组合 (borrowed from Rob Pike's slide) func generate(ch chan<- int) { for i := 2; ; i++ { ch <- i // Send 'i' to channel 'ch'. } } func filter(src <-chan int, dst chan<- int, prime int) { for i := range src { // Loop over values received from 'src'. if i%prime != 0 { dst <- i // Send 'i' to channel 'dst'. } } } func sieve() { ch := make(chan int) // Create a new channel. go generate(ch) // Start generate() as a subprocess. for { prime := <-ch fmt.Print(prime, "\n") ch1 := make(chan int) go filter(ch, ch1, prime) ch = ch1 } } 

8 .sieve.go (cont.) From divan's blog (http://divan.github.io/posts/go_concurrency_visualize/) 

9 .思考 面对同一个问题，来自不同编程语言的程序员给出了思维方式截然不同的解决方法 一定程度上印证了前面的假说：编程语言影响编程思维 避免Go coding in c way/in java way/in python way... 目标：Go coding in go way 

10 .编程语言思维的形成 根本：价值观决定思维和语言结构 核心：思维和语言结构影响语言的应用行为 反馈：语言的应用行为反过来持续影响/优化语言结构 

11 .Go语言价值观 Go编程思维的形成深受Go语言价值观的影响 Go语言价值观的形成和内容 Go语言价值观主导下的Go编程思维 

12 .Go语言价值观形成 - 语言设计者&Unix文化(主导） (从左到右) Robert Griesemer, Rob Pike和Ken Thompson 

13 .Go语言价值观形成 - Go语言的遗传基因 The task of the programming language designer " is consolidation not innovation ". (Tony Hoare, 1973, Go并发模型最初CSP的提出者). 

14 .Go语言价值观形成 - 面向新的基础设施环境和大规模软件开发的诸多问题(初 衷) 新的基础设施环境: 大规模云计算数据中心 多核以及多处理器硬件体系 大规模软件开发的难题(Google内部）： slow builds uncontrolled dependencies each programmer using a di erent subset of the language poor program understanding (documentation, etc.) duplication of e ort cost of updates cross-language builds 

15 .Go语言的价值观 Overall Simplicity Orthogonal Composition Preference in Concurrency 一句话概括Go的价值观：" orthogonal composition of simple concepts with preference in concurrency ". 

16 .Go语言的价值观(cont.) 价值观 (价值观下的)语言设计 编程思维 该编程思维在语言设计、标准库实现以及主流Go开源项目中的应用体现 

17 .Overall Simplicity 

18 .语言设计 "Simplicity & elegance are unpopular because they require hard work & discipline to achieve & education to be appreciated." - 图灵奖获得者Dijkstra(迪杰斯特拉) "Overall Simplicity"价值观更多地体现在了Go语言设计层面： clean and regular(mostly) syntax only 25 keywords one way to write a piece of code and minimize programmer's e ort garbage collection goroutines constants interfaces packages 

19 .short naming thought 短小 一致 在上下文环境中用最短的名字携带足够的信息 java vs. go "index" vs. "i" "value" vs. "v" 

20 .变量命名统计 cat $(find $GOROOT -name '*.go') | indents | sort | uniq -c | sort -nr | sed 30q 60224 v 42444 err 38012 t 33386 x 33302 i 33277 b 27943 p 25121 s 21228 n 20831 r 20634 _ 19236 c 17056 y 12850 f 12834 a ... ... 

21 .常见的变量短命名含义 [v, k, i] // loop varible for i, v := range s { for k, v := range m { for v := range r { // channel // if、switch/case clause varible if v := mimeTypes[ext]; v != "" { switch v := ptr.Elem(); v.Kind() { case v := <-c: v := reflect.ValueOf(x) // result of reflect.Value() [t] t := time.Now() // time t := &Timer{ // timer if t := md.typemap[off]; t != nil { // type [b] b := make([]byte, n) // bytes slice b := new(bytes.Buffer) // bytes.Buffer 

22 .minimal thought "一种"代码写法，或提供最少的写法、更简单的写法 Go is not a “TMTOWTDI—There’s More Than One Way To Do It” 显而易见的代码，而不是"聪明"的代码 minimize programmer's e ort Least concern about coding style: - Gofmt's style is no one's favorite, yet gofmt is everyone's favorite. 

23 ."一种"循环: for 常规 for i := 0; i < count; i++ {} "while" for condition { } "do-while" for { // use "for-break" instead doSomething() if condition { break } } iterator loop for k, v := range f.Value {} dead loop for {} 

24 ."一种"constants constants只是数字，无需显式赋予类型 const incomingQueueLength = 25 const ( http2minMaxFrameSize = 1 << 14 http2maxFrameSize = 1<<24 - 1 ) const PI = 3.1415928 const e = 1E6 无需算术转换 const a = 10080 var c int32 = 99 d := c + a fmt.Printf("%T\n", d) //int32 fmt.Printf("%T\n", a) //int 

25 ."一种"错误处理方法 There are only two kinds of language: the ones people complain about, and the ones nobody uses. - Bjarne Stroustrup 基于比较的错误处理, 没有针对exception的"try-catch"的控制结构 让使用者更聚焦于错误本身，显式地处理每一个error，让你对代码更加自信 不增加语言复杂性：错误值和其他类型的值地位是一样的，错误处理代码也是普通代码， 并无特殊之处。 "We believe that coupling exceptions to a control structure, as in the try-catch-finally idiom, results in convoluted code.(go faq)" 

26 .错误处理模式 使用error类型作为错误码返回类型，而不是其他类型（比如int） 最常见的 callee: return errors.New("something error") or return fmt.Errorf("something error: %s", "error reason") caller: if err != nil {... } 导出的error变量 // io/io.go var ErrShortWrite = errors.New("short write") var ErrShortBuffer = errors.New("short buffer") if err := doSomeIO(); err == io.ErrShortWrite { ... } 

27 .错误处理模式(cont.) 定义新的错误类型实现定制化错误上下文 // encoding/json/decode.go type UnmarshalTypeError struct { Value string // description of JSON value - "bool", "array", "number -5" Type reflect.Type // type of Go value it could not be assigned to Offset int64 // error occurred after reading Offset bytes Struct string // name of the struct type containing the field Field string // name of the field holding the Go value } func (e *UnmarshalTypeError) Error() string { ... ... return "json: cannot unmarshal " + e.Value + " into Go value of type " + e.Type.String() } if serr, ok := err.(*UnmarshalTypeError); ok { //use serr to access context in UnmarshalTypeError ... ... } 

28 .错误处理模式(cont.) 将某个包中的Error Type归类，统一提取出一些公共行为特征 将这些公共行为特征(behaviour)放入一个公开的interface中 以stdlib的net package为例： //net/net.go type Error interface { error Timeout() bool // Is the error a timeout? Temporary() bool // Is the error temporary? } net/http/server.go中的使用举例： rw, e := l.Accept() if e != nil { if ne, ok := e.(net.Error); ok && ne.Temporary() { ... .. } ... ... } 

29 .错误处理模式(cont.) 一个实现了net.Error的Error type的实现 //net/net.go type OpError struct { ... ... // Err is the error that occurred during the operation. Err error } type temporary interface { Temporary() bool } func (e *OpError) Temporary() bool { if ne, ok := e.Err.(*os.SyscallError); ok { t, ok := ne.Err.(temporary) return ok && t.Temporary() } t, ok := e.Err.(temporary) return ok && t.Temporary() }