Golang：调用将项添加到数组的方法后，数组为空[重复]

Question

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I am new to Golang. I have this simple code, that I can't get to work; the problem is that after call the method LoadGroups, the "main" function doesn't see the changes:

package main

import "fmt"

type Group struct {
    Name string
}

type Configuration struct {
    Groups []Group
}

func NewConfiguration() (error, *Configuration) {
    conf := Configuration{}
    conf.LoadGroups()
    fmt.Print("Final number of groups: ", len(conf.Groups))
    return nil, &conf
}

func (conf Configuration) LoadGroups() {
    for i := 0; i < 5; i++ {
        conf.Groups = append(conf.Groups, Group{Name: "Group " + string(i)})
        fmt.Println("Current number of groups: ", len(conf.Groups))
    }
}

func main() {
    NewConfiguration()
}

Playground: https://play.golang.org/p/VyneKpjdA-

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Answer 1

You are modifying a copy of the Configuration, not the Configuration itself.

The method LoadGroups should take a pointer to a Configuration instead:

package main

import "fmt"

type Group struct {
    Name string
}

type Configuration struct {
    Groups []Group
}

func NewConfiguration() (error, *Configuration) {
    conf := &Configuration{}
    conf.LoadGroups()
    fmt.Print("Final number of groups: ", len(conf.Groups))
    return nil, conf
}

func (conf *Configuration) LoadGroups() {
    for i := 0; i < 5; i++ {
        conf.Groups = append(conf.Groups, Group{Name: "Group " + string(i)})
        fmt.Println("Current number of groups: ", len(conf.Groups))
    }
}

func main() {
    NewConfiguration()
}