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152 lines
2.7 KiB
Markdown
152 lines
2.7 KiB
Markdown
# 附录B：有趣的代码片段
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这里收集一些比较有意思的Go程序片段。
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## 自重写程序
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UNIX/Go语言之父 Ken Thompson 在1983年的图灵奖演讲 Reflections on Trusting Trust 就给出了一个C语言的自重写程序。
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最短的C语言自重写程序是 Vlad Taeerov 和 Rashit Fakhreyev 的版本：
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```c
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main(a){printf(a="main(a){printf(a=%c%s%c,34,a,34);}",34,a,34);}
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```
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下面的Go语言版本自重写程序是 [rsc](https://research.swtch.com/zip) 提供的：
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```go
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/* Go quine */
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package main
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import "fmt"
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func main() {
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fmt.Printf("%s%c%s%c\n", q, 0x60, q, 0x60)
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}
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var q = `/* Go quine */
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package main
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import "fmt"
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func main() {
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fmt.Printf("%s%c%s%c\n", q, 0x60, q, 0x60)
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}
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var q = `
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```
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在 golang-nuts 中还有很多版本：
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```go
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package main;func main(){c:="package main;func main(){c:=%q;print(c,c)}";print(c,c)}
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```
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```go
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package main;func main(){print(c+"\x60"+c+"\x60")};var c=`package main;func main(){print(c+"\x60"+c+"\x60")};var c=`
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```
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如果有更短的版本欢迎告诉我们。
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## 三元表达式
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```go
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func If(condition bool, trueVal, falseVal interface{}) interface{} {
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if condition {
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return trueVal
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}
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return falseVal
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}
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a, b := 2, 3
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max := If(a > b, a, b).(int)
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println(max)
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```
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## 禁止 main 函数退出的方法
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```go
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func main() {
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defer func() { for {} }()
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}
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func main() {
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defer func() { select {} }()
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}
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func main() {
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defer func() { <-make(chan bool) }()
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}
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```
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## 基于管道的随机数生成器
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随机数的一个特点是不好预测。如果一个随机数的输出是可以简单预测的，那么一般会称为伪随机数。
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```go
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func main() {
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for i := range random(100) {
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fmt.Println(i)
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}
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}
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func random(n int) <-chan int {
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c := make(chan int)
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go func() {
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defer close(c)
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for i := 0; i < n; i++ {
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select {
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case c <- 0:
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case c <- 1:
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}
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}
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}()
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return c
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}
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```
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基于select语言特性构造的随机数生成器。
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## Assert测试断言
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```go
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type testing_TBHelper interface {
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Helper()
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}
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func Assert(tb testing.TB, condition bool, args ...interface{}) {
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if x, ok := tb.(testing_TBHelper); ok {
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x.Helper() // Go1.9+
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}
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if !condition {
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if msg := fmt.Sprint(args...); msg != "" {
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tb.Fatalf("Assert failed, %s", msg)
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} else {
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tb.Fatalf("Assert failed")
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}
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}
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}
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func Assertf(tb testing.TB, condition bool, format string, a ...interface{}) {
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if x, ok := tb.(testing_TBHelper); ok {
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x.Helper() // Go1.9+
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}
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if !condition {
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if msg := fmt.Sprintf(format, a...); msg != "" {
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tb.Fatalf("Assertf failed, %s", msg)
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} else {
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tb.Fatalf("Assertf failed")
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}
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}
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}
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func AssertFunc(tb testing.TB, fn func() error) {
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if x, ok := tb.(testing_TBHelper); ok {
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x.Helper() // Go1.9+
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}
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if err := fn(); err != nil {
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tb.Fatalf("AssertFunc failed, %v", err)
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}
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}
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```
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