Question

我有以下struct，其功能可以更新其字段：

type Dog struct {
    name string
    age  int
}

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

上面的方法可以正常工作。但是，当struct属于另一个对象并且所述对象告诉struct更新其字段时，更改似乎发生了，但没有应用：

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.
}

我认为我必须以某种方式使用pointers，但不能完全弄清楚。

Answer 1

如果您希望方法修改接收者的状态，则该方法的接收者的类型应为指针类型。

也就是说，与声明growOld方法的方式相同，tellDogToGrowOld方法还应具有一个指针接收者：

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

或者，您可以将要修改的字段设置为指针，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()
}

Answer 2

将所有者中的字段设置为*狗不是狗

type Owner struct {
    dog *Dog
}

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

    return owner
}

从主要用途＆dog呼叫时

var dog Dog
    dog.name = "dog"

    owner := newOwner(&dog)

https://play.golang.org/p/LpFqW09dOs4

当另一个对象告诉Struct更新时Struct字段未更新

2 个答案: