Append values to array inside of map golang

Question

I am trying to append values to arrays inside of a map:

var MyMap map[string]Example 

type Example struct {
    Id []int
    Name []string
}

Here is what i tried but i can not point to an object of Example to append to arrays.

package main


import (
  "fmt"
)


type Example struct {
  Id []int
  Name []string
}

func (data *Example) AppendExample(id int,name string) {
   data.Id = append(data.Id, id)
   data.Name = append(data.Name, name)
}

var MyMap map[string]Example

func main() {
   MyMap = make(map[string]Example)
   MyMap["key1"] = Oferty.AppendExample(1,"SomeText")
   fmt.Println(MyMap)
}

I thought i solved the problem but what i did does not solve it as i need to assign value on the key matching in a loop. — Saem
– Saem, Commented Nov 11, 2017 at 17:16

Bohdan Kostko · Accepted Answer · 2017-11-13 16:25:24Z

16

You need to create an instance of your Example struct before putting it into the map.

Also your map keeps copy of your struct, not a struct itself according to MyMap definition. Try to keep the reference to your Example struct within the map instead.

package main

import "fmt"

type Example struct {
    Id []int
    Name []string
}

func (data *Example) AppendOffer(id int, name string) {
    data.Id = append(data.Id, id)
    data.Name = append(data.Name, name)
}

var MyMap map[string]*Example

func main() {
    obj := &Example{[]int{}, []string{}}
    obj.AppendOffer(1, "SomeText")
    MyMap = make(map[string]*Example)
    MyMap["key1"] = obj
    fmt.Println(MyMap)
}

Pozdrawiam!

edited Nov 13, 2017 at 16:25

answered Nov 11, 2017 at 17:28

Bohdan Kostko

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3 Comments

Saem Over a year ago

Yeah, i did exactly the same thing as well as i couldn't find how to do without creating an object of struct. I will undelete my own answer. Thank you for input!

Bohdan Kostko Over a year ago

Not really the same. You're still using struct literal instead of a pointer in your map. Please read more about structs and pointers here: gobyexample.com/pointers gobyexample.com/structs

ak76 Over a year ago

instead of obj := &Example{[]int{}, []string{}} use obj1 := new(Example) see Exampe in Go Playground

Saem · Accepted Answer · 2017-11-11 17:09:20Z

0

Okay, i solved it by creating an Example object and then appending values to its array and assigning it to map.

Like this:

package main


import (
 "fmt"
)


type Example struct {
  Id []int
  Name []string
}

func (data *Example) AppendExample(id int,name string) {
   data.Id = append(data.Id, id)
   data.Name = append(data.Name, name)
}

var MyMap map[string]Example

func main() {

  var object Example
  object.AppendExample(1,"SomeText")

  MyMap = make(map[string]Example)
  MyMap["key1"] = object
  fmt.Println(MyMap)
}

answered Nov 11, 2017 at 17:09

Saem

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