给 Golang 结构体字段赋值 [英] Assign a new value to Golang structure field

问题描述

结构字段有问题.

我创建了一个 Point 类，使用一个方法 Move() 通过 dx<增加或减少对象变量 x/代码>.另一种方法Print用于输出结果.

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.

在main() 中创建一个新实例，默认x = 3 和dx = 2，然后我调用Move() 和 Print().我希望 x 的值在 Move() 和 Print() 期间改变将产生 Final x=5, 而不是显示这个:

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

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()
}

推荐答案

此处需要使用指针，否则每次都只更改原始对象的副本.一切都是在 go 中按值传递.

You need to use a pointer 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()
}

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