go defer

    conn, err := websocket.Upgrade(w, req, w.Header(), bufSize, bufSize)
    if err != nil {
        code = errWSUpgradeFailed
        msg = err.Error()
        return
    }
    defer conn.Close()

defer conn.Close() 要放在判err之后，因为err时conn为nil，然后nil.Close()会使程序出错，甚至直接panic崩调

    code := Success
    msg := ""
    var response responseJSON
    defer func() {
        writeResponse(msg, response, w, code)
    }()

defer执行匿名函数

package main
import "fmt"
func f1() (result int) {
    println("-------------------------------")
    defer func() {
        result++
    }()
    return 0
}
func f2() (r int) {
    println("-------------------------------")
     t := 5
     defer func() {
       t = t + 5
     }()
     return t
}
func f3() (r int) {
    println("-------------------------------")
    defer func(r int) {
          r = r + 5
    }(r)
    return 1
}
func f4() (r int) {
    println("-------------------------------")
    r=100
    return
}
func f5() (r1 int,r2 interface{},r3 string) {
    println("-------------------------------")
    return
}
func f6() (r1 int) {
    println("-------------------------------")
    defer func() {
        if r1==100 {
            println("r1==100")
        }
    }()
    r1=100
    return
}
func f7() (r1 int) {
    println("-------------------------------")
    r1=100
    return 1
}
func f8() (r1 int) {
    println("-------------------------------")
    r1=100
    defer func() {
        r1++;
    }()
    return 1
}
func f9() (r1 int) {
    println("-------------------------------")
    defer func(r int) {
        r++
    }(r1)
    return
}
func f10() (r interface{}) {
    println("-------------------------------")
    r=1
    defer func(a interface{}) {
        fmt.Println("a:",a)
        fmt.Println("r:",r)
        a=100
        fmt.Println("a:",a)
        fmt.Println("r:",r)
    }(r)
    return
}
func f11() (r interface{}) {
    println("-------------------------------")
    r=1
    defer func(a interface{}) {
        fmt.Println("a:",a)
        fmt.Println("r:",r)
        a=100
        fmt.Println("a:",a)
        fmt.Println("r:",r)
    }(r)
    r=2
    defer func(a interface{}) {
        fmt.Println("second a:",a)
        fmt.Println("second r:",r)
        a=200
        fmt.Println("second a:",a)
        fmt.Println("second r:",r)
    }(r)
    return
}
func f12() (r interface{}) {
    println("-------------------------------")
    r=1
    defer func(a interface{}) {
        fmt.Println("a:",a)
        fmt.Println("r:",r)
        a=100
        fmt.Println("a:",a)
        fmt.Println("r:",r)
    }(r)
    r=2
    defer func(a interface{}) {
        fmt.Println("second a:",a)
        fmt.Println("second r:",r)
        a=200
        fmt.Println("second a:",a)
        fmt.Println("second r:",r)
    }(r)
    r=3
    return
}
func f13() (a interface{},b interface{}) {
    println("-------------------------------")
    return 1,2
}
func f14() map[string]string{
    println("-------------------------------")
    a:=map[string]string{"a":"b"}
    defer func(mp map[string]string) {
        mp["a"]="c"
    }(a)
    return a
}
func f15() string{
    println("-------------------------------")
    a:="a"
    defer func(mp string) {
        mp="b"
    }(a)
    return a
}
func f16() []byte{
    println("-------------------------------")
    a:=[]byte("a")
    defer func(mp []byte) {
        mp=[]byte("b")
    }(a)
    return a
}
func f17() chan int{
    println("-------------------------------")
    a:=make(chan int,10)
    defer func(mp chan int) {
        mp<-1
    }(a)
    return a
}
func main() {
    println(f1())
    println(f2())
    println(f3())
    println(f4())
    a,b,c:=f5()
    fmt.Println(a,b,c)
    println(f6())
    println(f7())
    println(f8())
    println(f9())
    fmt.Println(f10())
    fmt.Println(f11())
    fmt.Println(f12())
    e,f:=f13()
    fmt.Println(e,f)
    fmt.Println(f14())
    fmt.Println(f15())
    fmt.Println(string(f16()))
    fmt.Println(len(f17()))
}

-------------------------------
1
-------------------------------
5
-------------------------------
1
-------------------------------
100
-------------------------------
0 <nil> 
-------------------------------
r1==100
100
-------------------------------
1
-------------------------------
2
-------------------------------
0
-------------------------------
a: 1
r: 1
a: 100
r: 1
1
-------------------------------
second a: 2
second r: 2
second a: 200
second r: 2
a: 1
r: 2
a: 100
r: 2
2
-------------------------------
second a: 2
second r: 3
second a: 200
second r: 3
a: 1
r: 3
a: 100
r: 3
3
-------------------------------
1 2
-------------------------------
map[a:c]
-------------------------------
a
-------------------------------
a
-------------------------------
1

defer会从下往上执行，若return时没到达的defer不执行，

非匿名函数

func(a interface{},b interface{}) (c interface{},d interfacd{}) {

c=3

d=4

return

return 1,2

}

c和d在进入函数时定义，一旦return，c和d的值都会返回，如果return 1,2，则1,2的值会赋给c，d，return时要么都不赋值，要么都赋值，不能只赋部分

对于匿名函数func(a interface{}) {

 a=1

}(r)

表示将r传入函数作为a的值，除了chan和map，别的一定是复制传入(interface{},[]byte,etc)，不会传入指针，而且a的值是运行函数时r的值