学习golang过程中遇到的坑

defer与panic

func中defer是队列形式存储的，panic执行后面的defer不加入队列

package main

import (
    "fmt"
)

func main() {
    defer_call()
}

func defer_call() {
    defer func() { fmt.Println("打印前") }()
    defer func() { fmt.Println("打印中") }()
    defer func() { fmt.Println("打印后") }()

    panic("触发异常")
}

range 重用地址

range 循环，会重用地址，也就是说，for _, stu := range stus 中的 stu 总是在同一个地址

type student struct {
    Name string
    Age  int
}

func pase_student() {
    m := make(map[string]*student)
    stus := []student{
        {Name: "zhou", Age: 24},
        {Name: "li", Age: 23},
        {Name: "wang", Age: 22},
    }
    for _, stu := range stus {
        m[stu.Name] = &stu
    }
}

select里面的case条件是随机性的

func main() {
    runtime.GOMAXPROCS(1)
    int_chan := make(chan int, 1)
    string_chan := make(chan string, 1)
    int_chan <- 1
    string_chan <- "hello"
    select {
    case value := <-int_chan:
        fmt.Println(value)
    case value := <-string_chan:
        panic(value)
    }
}

defer的匿名函数参数是拷贝地址的（如果是指针就是最后指针的值），而函数里面的函数是优先在main函数体中执行的

func calc(index string, a, b int) int {
    ret := a + b
    fmt.Println(index, a, b, ret)
    return ret
}

func main() {
    a := 1
    b := 2
    defer calc("1", a, calc("10", a, b))
    a = 0
    defer calc("2", a, calc("20", a, b))
    b = 1
}

append 是往后面追加数据

func main() {
    s := make([]int, 5)
    s = append(s, 1, 2, 3)
    fmt.Println(s) // 输出 0 0 0 0 0 1 2 3
}

interface接口 不通的对象类型对应了不同的方法集，从而影响interface接口实现的对象

Methods Receivers         Values
-----------------------------------------------
(t T)                     T and *T

(t *T)                    *T

package main

import (
    "fmt"
)

type People interface {
    Speak(string) string
}

type Stduent struct{}

func (stu *Stduent) Speak(think string) (talk string) {
    if think == "bitch" {
        talk = "You are a good boy"
    } else {
        talk = "hi"
    }
    return
}

func main() {
    var peo People = Stduent{}
    think := "bitch"
    fmt.Println(peo.Speak(think)) //指针类型的receiver 方法实现接口时，只有指针类型的对象实现了该接口 需要改成var peo People = &Stduent{}
}

实现了interface接口的类调用的时候其实已经拷贝了一份新的数据在使用了（地址不一样）

package main

import (
    "fmt"
)

type People interface {
    Show()
}

type Student struct{}

func (stu *Student) Show() {

}

func live() People {
    var stu *Student
    return stu
}

func main() {
    if live() == nil {
        fmt.Println("AAAAAAA")
    } else {
        fmt.Println("BBBBBBB")  //输出的时BBB live() 实际上是 var stu *Student var p People p=stu
    }
}

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