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• About this project

  Go by Example is a hands-on introduction to Go using annotated example programs

• Time

  2023-09-04 ~

• Toc

Harvest

1. Import

   import "Mod/Package"

2. e

   以10为底, 并不是以e为底 5e3 = 5000

3. switch

   对于多种条件的判断更为灵活

4. slice

   make([]type,num) 使用make声明且最好预先分配内存

   添加元素append

   go 1.21以后可以用slices包

5. values in map

   if _,prs := m["key"]; prs{ 
       return true 
   }else{
       return false
   }
   

6. 闭包Closure

   闭包在返回函数的同时还记录了上下文环境（把里面的变量封闭在了闭包里面）

   "The returned function closes over the variable i to form a closure." ---GoByExample

   封闭了的包，把外层函数里面的变量环境也存储在了二层函数里面，并且将用到的变量封闭在里面 。

   //Todo 闭包是返回了二层函数，所以一层函数的作用就是提供变量的生命周期？

7. strings

   Go string 是只读的bytes数组的切片, string == []byte

   In other languages, strings are made of “characters”. In Go, the concept of a character is called a rune - it’s an integer that represents a Unicode code point.

   https://go.dev/blog/strings

8. methods

   Go supports methods defined on struct types.

   也就是说方法只能在自定义的type上

9. Select

   select lets you wait on multiple channel operations.

   select 语句只能用于通道操作，每个 case 必须是一个通道操作，要么是发送要么是接收。

   select 语句会监听所有指定的通道上的操作，一旦其中一个通道准备好就会执行相应的代码块。

10. Timeouts

Timeouts are important for programs that connect to external resources or that otherwisse need to bound execution time. Implementing timeouts in Go is easy and elegant thanks to channels and select

11. Non-Blocking Channel Operations

Basic sends and receives on channels are blocking. However, we can use select with a default clause to implement non-blocking sends, receives, and even non-blocking multi-way selects.

12. 无缓冲通道

无缓冲通道指在获取数据之前没有能力保存数据的通道，这种类型的通道要求亮哥Goroutine同时处于执行状态才能完成写入和获取

如果两个Goroutine没有同时准备，某一个Goroutine执行写入或获取操作将会处于阻塞等待状态，另一个Goroutine无法执行写入或获取操作， 程序将会提示异常，这种类型的通道执行写入和获取的交互行为是同步，任意一个操作都无法离开另一个操作单独存在

当我们使用无缓冲通道的时候，必须注意通道变量的操作， 确保程序中有两个或两个以上的Goroutine同时执行通道的读写操作，读写操作必须是一读一写，不能只读不写或只写不读

13. go 闭包在循环中

func main() {
    done := make(chan bool)

    values := []string{"a", "b", "c"}
    for _, v := range values {
        go func() {
            fmt.Println(v)
            done <- true
        }()
    }

    // wait for all goroutines to complete before exiting
    for _ = range values {
        <-done
    }
}

期望输出：a, b, c 实际有可能的输出：c, c, c

这是因为循环的每次迭代都用相同的实例变量v，所以每个闭包共享相同的变量。 当闭包运行时，在fmt.Println语句执行时输出变量v， 但是v有可能在goroutine启动时被修改。 想要检测这种问题可以用go vet

为了绑定每个闭包在启动时的变量v，我们最有可能在循环内为每次迭代新建一个变量， 其其中一种办法时将变量作为参数传进闭包：

for _,v :=range values {
    go func(u string) {
        fmt.Println(u)
        done <- true
    }(v)
}

另一种更简单的办法是用声明的方式创建一个变量，有可能看起来奇怪但是有用：

for _,v := range values {
    v:=v //create a new 'v'
    go func() {
        fmt.Println(v)
        done <- true
    }()
}

15. defer

defer 用于确保函数调用再程序执行的一会儿后调用，通常用于清除的场景。

16. recover

go通过 recover内置函数可以让程序从panic中恢复，停止panic并执行defer闭包

**recover 必须在defer函数中调用，**当发生panic时，defer会激活并且recover调用会捕捉panic，此时程序会将defer执行完后再结束

Log

日期	内容	收获	Key
2023-09-04	"helloworld, Values, Variables, Constants"	harvest 1,2
2023-09-06	"For, If/Else, Switch, Arrays, Slices"	harvest 3,4
2023-09-07	"Maps, Range, Functions, Multiple Return Values, Variadic Functions"	harvest 5,6	Closure
2023-09-09	"Closure, Recursion, Pointers, Strings and Runes, Structs, Methods, Interfaces, Struct Embedding,Generics"	harvest 7,8	Strings & Runes
2023-09-10	"Errors, Goroutines, Channels, Channel Buffering, ChannelSynchronization, Channel Directions, Select, Timeouts"	harvest 9,10	Timeouts
2023-09-11	"Timeouts, Non-blocking channel operation, Close channel, channel sychronization"	harvest 11,12	unbuffered channel
2023-09-15	“Range chan, timers, rickers worker pools, waitGroups”	harvest 13	waitGroups
2023-09-27	"rateLimiting, atomicCounter, mutexes"
2023-10-02	"stateful goroutines,sort,sore by functions, panic, defer, recover"		stateful goroutines
2023-10-17	"String Functions","String Formatting","Text Templates","Regular Expressions","JSON","XML","Time","Epoch","Time Formatting / Parsing","Random Numbers","Number Parsing","Url parsing"		Url parsing