英文:
Modifying a struct slice within a struct in Go
问题
在下面的示例中，一个 person 拥有一组 friendship 的切片，我试图将一个 friendship 初始化为指向另一个 person 对象的指针，但由于某种原因失败了，结果是没有人有任何 friendship。我是否在某个地方没有正确使用指针？
package main
import (
"fmt"
"math/rand"
)
type friendship struct {
friend *person
}
type person struct {
name int
friendship []friendship
}
func createPerson(id int) person {
return person{id, make([]friendship, 0)}
}
func (p *person) addFriends(possibleFriends []*person, numFriends int) {
var friend *person
for i := 0; i < numFriends; i++ {
friend = possibleFriends[rand.Intn(len(possibleFriends))]
p.friendship = append(p.friendship, friendship{friend})
}
}
func main() {
numPeople := 20
people := make([]person, numPeople)
possibleFriends := make([]*person, numPeople)
for i := 0; i < numPeople; i++ {
people[i] = createPerson(i)
possibleFriends[i] = &(people[i])
}
for _, p := range people {
p.addFriends(possibleFriends, 2)
}
fmt.Println(people)
}
以下是翻译好的代码部分，不包括问题部分。
英文:
In the following example, a person has a slice of friendships, and I try to initialize a friendship as a pointer to another person object, but for some reason it fails, and the result is that nobody has any friendships. Am I not using a pointer somewhere where I should be?
package main
import (
"fmt"
"math/rand"
)
type friendship struct {
friend *person
}
type person struct {
name int
friendship []friendship
}
func createPerson(id int) person {
return person{id, make([]friendship, 0)}
}
func (p *person) addFriends(possibleFriends []*person, numFriends int) {
var friend *person
for i := 0; i < numFriends; i++ {
friend = possibleFriends[rand.Intn(len(possibleFriends))]
p.friendship = append(p.friendship, friendship{friend})
}
}
func main() {
numPeople := 20
people := make([]person, numPeople)
possibleFriends := make([]*person, numPeople)
for i := 0; i < numPeople; i++ {
people[i] = createPerson(i)
possibleFriends[i] = &(people[i])
}
for _, p := range people {
p.addFriends(possibleFriends, 2)
}
fmt.Println(people)
}
答案1
得分: 2
使用以下代码替换原始代码中的部分内容：
for i := 0; i < numPeople; i++ {
people[i].addFriends(possibleFriends, 2)
}
或者
for i, _ := range people {
people[i].addFriends(possibleFriends, 2)
}
替代原始代码中的部分：
for _, p := range people {
p.addFriends(possibleFriends, 2)
}
这是因为p是people[i]的副本，对切片people的addFriends操作没有影响。
英文:
use
for i := 0; i < numPeople; i++ {
people[i].addFriends(possibleFriends, 2)
}
or
for i, _ := range people {
people[i].addFriends(possibleFriends, 2)
}
instead of
for _, p := range people {
p.addFriends(possibleFriends, 2)
}
this is because p is a copy of people[i], addFriends has no effect on slice people
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