在Go中干净地实现多级结构

Question

I'm new to Golang, and I'm trying to initialize a struct of structs with a list of strings at the bottom. I'd like to be able to access the values inside in a clean and readable way, but it isn't clicking.

for example, the struct setup is as follows:

type config struct {
  // a config can have many replicas
  configName string
  replicas  []string
}

type instance struct {
  // an instance can have many configs
  name string
  configs   []config
}

type user struct {
  // a user can have up to two instances
  instances []instance
}

And I'm initializing it like so:

var users = map[string][]user{
  "user-1": []user {
    { 
      []instance {
        {
          "instance-1",
          []config {
            {
              "some-config-1",
              []string{"xx", "yy", "zz",},
            },
          },
        },
      }, 
    },
  },
  "user-2": {
    { 
      []instance {
        {
          "instance-2",
          []config {
            {
              "some-config-2",
              []string{"xx", "yy", "zz",},
            },
          },
        },
      }, 
    },
  },
}

Then, to access any of the fields, I have to do gross stuff like:

func main() {
  for user, _ := range users {
    fmt.Println(users[user][0].instances[0].name)
  }
}

There must be a better way? Running (but gross) code example here: http://play.golang.org/p/9M8pyBnMPB

Answer 1

Just write functions.

func NewInstance(n string, confs ...config) instance {
    var i instance
    i.name = n
    i.configs = confs
    return i
}

func NewConfig(name string, reps ...string) config {
    var c config
    c.configName = name
    c.replicas = reps
    return c
}

func NewUser(ins ...instance) user {
    var u user
    u.instances = ins
    return u
}

Then this has the same effect as your code:

var users map[string][]user
func main() {
    users = make(map[string][]user)
    u1_i1 := NewInstance("instance-1", 
    NewConfig("conf1", "xx", "yy", "zz"))

    users["user-1"] = []user{NewUser(u1_i1)}

    u2_i1 := NewInstance("instance-2",
    NewConfig("conf2", "xx", "yy", "zz", "aa"))

    users["user-2"] = []user{NewUser(u2_i1)}

    for user, _ := range users {
        fmt.Println(users[user][0].instances[0].name)
    }
}

http://play.golang.org/p/okmBapuDWj

If accessing things gets complicated.. more functions:

func (u user) InstanceName(i int) string {
    return u.instances[i].name
}

or consider reworking your data structures.