突变值
问题描述：
Can someone please tell me how to mutate the value of type Clock.
Basically when I call New() I get the output 3:04 and after calling ADD() function I expect the value to be 03:09. If I assign the value of ADD() function call then I get 03:09 as output. I was wondering is it possible to mutate the value of the type Clock using pointers?
package main
import "fmt"
const testVersion = 4
type Clock int
func New(hour, minute int) Clock {
result := (hour*60 + minute) % (24*60)
if result < 0 {
result = result + 24*60
}
return Clock(result)
}
func (c Clock) String() string {
return fmt.Sprintf("%02v:%02v", int(c/60), int(c%60))
}
func (c Clock) Add(minutes int) Clock{
newC:=New(0,minutes + int(c))
//fmt.Println(a)
}
func main() {
result := New(3, 4)
fmt.Println(result)
result.Add(5)
fmt.Println(result)
}
答
Yes, it is possible. If you are going to modify the value, you must define Add method on pointer receiver, e.g.
func (c *Clock) Add(minutes int) Clock{
*c =New(0,minutes + int(*c))
return *c
}
Basic rule is: use pointer receiver if you're going to change the receiver value (except for slice and map which act as reference). Take a look at the following materials for better understanding on method receiver:
The Go tour on Methods