英文:
Assign a new value to a struct field
问题
我有一个关于结构字段的问题。
我创建了一个名为Point的类，其中有一个方法Move()，它通过dx增加或减少对象变量x的值。另一个方法Print()用于输出结果。
在main()函数中，我创建了一个新的实例，其中x的默认值为3，dx的默认值为2，然后我调用了Move()和Print()方法。我期望在Move()方法中x的值会改变，并且Print()方法会输出Final x=5，但实际上它显示的是：
2014/07/28 15:49:44 New X=5
2014/07/28 15:49:44 Final X=3
我的代码有什么问题？
type Point struct {
x, dx int
}
func (s Point) Move() {
s.x += s.dx
log.Printf("New X=%d", s.x)
}
func (s Point) Print() {
log.Printf("Final X=%d", s.x)
}
func main() {
st := Point{ 3, 2 }
st.Move()
st.Print()
}
英文:
I have a problem with structure fields.
I've created a class Point with one method Move() that increases or decreases object variable x by dx. Another method Print is used to output results.
In main() a new instance is created with default x = 3 and dx = 2, then I call Move() and Print(). I expect that value of x is changed during Move() and Print() will produce Final x=5, but instead of it displays this:
2014/07/28 15:49:44 New X=5
2014/07/28 15:49:44 Final X=3
What's wrong with my code?
<!-- language: lang-golang -->
type Point struct {
x, dx int
}
func (s Point) Move() {
s.x += s.dx
log.Printf("New X=%d", s.x)
}
func (s Point) Print() {
log.Printf("Final X=%d", s.x)
}
func main() {
st := Point{ 3, 2 };
st.Move()
st.Print()
}
答案1
得分: 9
你需要在这里使用指针接收器，否则每次只会更改原始对象的副本。在Go语言中，所有东西都是按值传递的。
type Point struct {
x, dx int
}
func (s *Point) Move() {
s.x += s.dx
log.Printf("New X=%d", s.x)
}
func (s *Point) Print() {
log.Printf("Final X=%d", s.x)
}
func main() {
st := Point{ 3, 2 };
st.Move()
st.Print()
}
英文:
You need to use a pointer receiver here or you are only changing a copy of the original object every time. Everything is passed by value in go.
type Point struct {
x, dx int
}
func (s *Point) Move() {
s.x += s.dx
log.Printf("New X=%d", s.x)
}
func (s *Point) Print() {
log.Printf("Final X=%d", s.x)
}
func main() {
st := Point{ 3, 2 };
st.Move()
st.Print()
}
答案2
得分: 1
这是指针接收器和值接收器之间的区别。
这是指针接收器和值接收器之间的区别。
http://golang.org/doc/faq#methods_on_values_or_pointers
英文:
That's the difference between pointer receiver and value receiver
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