golang的注意事项

i := 10
j := 20
i , j = j, i

t := 3 + 5i
    fmt.Println(t) //(3+5i)
    fmt.Printf("type == %T", t)//type == complex128

var tmp int
    fmt.Scanf("%d", &tmp)
    fmt.Println("tmp == ", tmp)  //tmp ==  1
    var tmp2 int
    fmt.Scan(&tmp2)
    fmt.Printf("type == %T", tmp2)//type == int

type long int64
    var a long
    a = 2
    fmt.Printf("type == %T", a)  //type == main.long

num := 2
    switch num {
    case 1:
        fmt.Println("111")
    case 2:
        fmt.Println("222") //222
    case 3:
        fmt.Println("333")
    case 4:
        fmt.Println("4444")
    }

num := 2
    switch num {
    case 1:
        fmt.Println("111")
    case 2:
        fmt.Println("222") //222
        fallthrough
    case 3:
        fmt.Println("333") // 333
    case 4:
        fmt.Println("4444")
    }

score := 90
    switch {  //这里可以不用写 条件
    case score > 90:  //case 后面可以写条件
        fmt.Println("extent")
    case score > 80:
        fmt.Println("good")
    case score > 70:
        fmt.Println("not bad")
    }

func getname(args ...string) {
    length := len(args)
    if length > 0 {
        for i, data := range args {
            fmt.Printf("%d -- %s\n", i, data)
        }
    }
}
func test(args ...string) {
    getname(args[1:]...)  //只传递不定参数中的其中几个
}
func main() {
    test("qqq", "yyy", "bbb")
    //0 -- yyy
    //1 -- bbb
}

func Add(a, b int) int {
    return a + b
}
type Universal func(int, int) int
func main() {
    var uni Universal
    uni = Add
    res := uni(1, 2)
    fmt.Println(res)
}

func Add(a, b int) int {
    return a + b
}
type Universal func(int, int) int
func cal(uni Universal, a int, b int) int {
    return uni(a, b)
}
func main() {
    uni := Add
    res := cal(uni, 1, 2)
    fmt.Println(res)
}

name := "qqq"
    age := 24
    //1、匿名函数
    f1 := func() {
        fmt.Printf("name == %s\n", name)
        fmt.Printf("age == %d\n", age)
    }
    f1()
    //2、定义匿名函数的时候直接调用
    func(hobby string) {
        fmt.Println(name)
        fmt.Println(hobby)
    }("basketball")
    //3、定义匿名函数有参数有返回值
    f3 := func(a, b int) int {
        return a + b
    }
    fmt.Println(f3(1, 3))
    res := func(a, b int) int {
        return a + b
    }(3, 8)
    fmt.Println(res)

func cal() func() int {
    var x int
    return func() int {
        x++
        return x * x
    }
}
func main() {
    //1、闭包的特点1，可以捕获变量，且是以引用的方式捕获的
    a := 1
    name := "go"
    func() {
        a = 2
        name = "hello wrold"
        fmt.Printf("内部  ： a == %d, name == %s\n", a, name)
    }()
    fmt.Printf("外部  ： a == %d, name == %s\n", a, name)
    //2、必要的特点2 ，闭包里面使用的变量，只要闭包还在使用，则一直有效，哪怕超出该变量的作用域
    f := cal()
    fmt.Println(f())
    fmt.Println(f())
    fmt.Println(f())
    fmt.Println(f())
}

//延迟调用，main函数结束前进行调用
    fmt.Println("hello")
    defer fmt.Println("over!!")
    fmt.Println("world")
    //hello
    //world 
    //over!!
    //多个defer的执行顺序，类似于栈的方式，先进后出，哪怕中间出现程序错误，defer修饰的语句仍然会执行
    for i := 0; i < 10; i++ {
        defer fmt.Println(i)
    }
    --------------------------------------------
    defer fmt.Println("aaaa")
    defer fmt.Println("bbb")
    defer test(0)
    defer fmt.Println("ccc")
// ccc
// bbb
// aaaa
// panic: runtime error: integer divide by zero
// goroutine 1 [running]:
// main.test(0x0, 0x1)
//         F:/code/golang/golang_study/defer/main.go:6 +0x35
// main.main()
//         F:/code/golang/golang_study/defer/main.go:27 +0x134
// exit status 2

// a := 10
    // b := 20
    // defer func() {
    //  fmt.Printf("inner  a == %d, b == %d\n", a, b)
    // }()
    // a = 1
    // b = 2
    // fmt.Printf("externer  a == %d, b == %d\n", a, b)
// externer  a == 1, b == 2
// inner  a == 1, b == 2
    a := 10
    b := 20
    defer func(a, b int) {
        fmt.Printf("inner  a == %d, b == %d\n", a, b)
    }(a, b) //此处参数 a=10 b=20的参与已经传入到函数中了，只是匿名函数最后执行而已
    a = 1
    b = 2
    fmt.Printf("externer  a == %d, b == %d\n", a, b)
// externer  a == 1, b == 2
// inner  a == 10, b == 20

package maing
import (
    "fmt"
    "hhh/test"
)
var a int = 10
func init() {
    fmt.Println("this is main init")
}
func main() {
    a := "xiaozhu"
    fmt.Println(a)
    {
        a := 1.4
        fmt.Println(a)
    }
    test.Pr()
}

package test
import "fmt"
func init() {
    fmt.Println("test init")
}
func Pr() {
    fmt.Println("hello wrold")
}