golang 函数定义及其接口实例

/有返回值 且返回一个
func max(a int, b int) int {
    if a > b {
        return a
    }
    return b
}

//有返回值 且返回二个
func multi_ret(key string) (int, bool) {
    m := map[string]int{"ont": 1, "two": 2, "three": 3}
    var err bool
    var val int
    val, err = m[key]
    return val, err
}

//多个参数，相当于传进取一个数组
func sum(nums ...int) {
    fmt.Println(nums, " ")
    total := 0
    for _, num := range nums {
        total += num
    }
    fmt.Println(total)
}

//返回值为函数
func nextNum() func() int {
    i, j := 0, 1
    return func() int {
        var tmp = i + j
        i, j = j, tmp
        return tmp
    }
}

//递归 返回整数
func fact(n int) int {
    if n == 0 {
        return 1
    }
    return n * fact(n-1)
}

//结构
type rect struct {
    width  float64
    height float64
}

//结构函数
func (r *rect) area() float64 {
    return r.width * r.height
}

func (r *rect) perimeter() float64 {
    return 2 * (r.height * r.height)
}

//结构
type circle struct {
    radius float64
}

func (c *circle) area() float64 {
    return math.Pi * c.radius * c.radius
}
func (c *circle) perimeter() float64 {
    return 2 * math.Pi * c.radius
}

//接口   注意rect和circle均实现了shape接口
type shape interface {
    area() float64
    perimeter() float64
}

func interface_test() {
    r := rect{width: 2, height: 4}
    c := circle{radius: 4.3}
    s := []shape{&r, &c}
    for _, sh := range s {
        fmt.Println(sh)
        fmt.Println(sh.area())
        fmt.Println(sh.perimeter())
    }
}

//自定义错误
type myError struct {
    arg    int
    errMsg string
}

func (e *myError) Error() string {
    return fmt.Sprintf("%d - %s", e.arg, e.errMsg)
}

func error_test(arg int) (int, error) {
    if arg < 0 {
        return -1, errors.New("Bad Arguments, negtive")
    } else if arg > 256 {
        return -1, &myError{arg, "Bad Arguments, too large"}
    }
    return arg * arg, nil
}

func CopyFile(dstName string, srcName string) (written int64, err error) {
    src, err := os.Open(srcName)
    if err != nil {
        fmt.Println("open failed")
    }
    defer src.Close()
    dst, err := os.Create(dstName)
    if err != nil {
        fmt.Println("Create failed")
        return
    }
    defer dst.Close()
    return io.Copy(dst, src)

}