go - 当另一个对象告诉结构更新时结构字段不更新

Question

我有以下 struct，它具有可以更新其字段的功能:

type Dog struct {
    name string
    age  int
}

func (dog *Dog) growOld() {    
    dog.name = "old dog"
    dog.age++
}

以上内容单独运行良好。但是，当 struct 属于另一个对象并且该对象告诉 struct 更新其字段时，更改似乎发生但未应用:

package main

import (
    "fmt"
)

type Owner struct {
    dog Dog
}

func newOwner(dog Dog) Owner {
    var owner Owner
    owner.dog = dog

    return owner
}

func (owner Owner) tellDogToGrowOld() {
    owner.dog.growOld()
}

func main() {
    var dog Dog
    dog.name = "dog"

    owner := newOwner(dog)
    owner.tellDogToGrowOld()       

    fmt.Println(dog) // dog's name is still `dog` and age is 0.
}

我假设我必须以某种方式使用指针，但不太清楚如何。

Answer 1

如果您希望该方法修改接收者的状态，则该方法的接收者类型应该是指针类型。

也就是说，与声明growOld 方法的方式相同，tellDogToGrowOld 方法也应该有一个指针接收器:

func (owner *Owner) tellDogToGrowOld() {
    owner.dog.growOld()
}

或者，您可以将要修改的字段设为指针，例如:

type Owner struct {
    dog *Dog
}

func newOwner(dog *Dog) Owner {
    var owner Owner
    owner.dog = dog

    return owner
}

func (owner Owner) tellDogToGrowOld() {
    owner.dog.growOld()
}