Golang : Dealing with struct's private part



Tags : golang public private type struct methods

One of the most common things in Golang that easily confuse a newbie is how to declare variable/constant/identifier name properly. Many programmers are able to compile their code successfully, but left puzzled by missing/empty data after being processed. The reason is because the variable/identifier name starts with small cap and in essence turning the variable/identifier into a private type. (see https://golang.org/ref/spec#Exported_identifiers )

IF for some reason that you need to use a private variable inside a struct, the way to manipulate the private variable is to associate methods to it.

For the code example below, the email variable is private type inside the Person struct and the SetEmail() and Email() methods are created specifically to deal with the email variable.

Here you go :

 package main

 import "fmt"
 import "encoding/json"

 type Person struct {
  Name string // 1st letter cap is public, while small cap is private
  email  string
  Gender string
  Age int
 }

 func (p *Person) SetEmail(email string) {
  p.email = email
 }

 func (p Person) Email() string {
  return p.email
 }

 var v = []byte(`[
 {
 "name": "Denis Silva Costa",
 "email": "d*@gmail.com",
 "gender": "Male",
 "age": 27
 },
 {
 "name": "Ariana Cursino",
 "email": "a@a.com",
 "gender": "Female",
 "age": 31
 }
 ]`)

 func main() {

  var people []Person
  err := json.Unmarshal(v, &people)
  if err != nil {
  }

  // email WILL NOT be displayed because it is private
  fmt.Println(people)

  // set data to private variable via SetEmail method

  people[0].SetEmail("d@gmail.com")
  people[1].SetEmail("a@a.com")

  // Retrieve data from private variables via Email method
  fmt.Println(people[0].Email())
  fmt.Println(people[1].Email())

 }

Output :

[{Denis Silva Costa Male 27} {Ariana Cursino Female 31}]

d@gmail.com

a@a.com

Hope this short tutorial can be useful to new comers to Golang. Happy coding!

Oh, by the way, the original title for this article is "Golang : Dealing with private variable in struct". ;-)

Reference :

https://golang.org/ref/spec#Exported_identifiers

  See also : Golang : fmt.Println prints out empty data from struct



Tags : golang public private type struct methods

By Adam Ng

IF you gain some knowledge or the information here solved your programming problem. Please consider donating to the less fortunate or some charities that you like. Apart from donation, planting trees, volunteering or reducing your carbon footprint will be great too.


Advertisement