How to initialize a nested struct?
GoGo Problem Overview
I cannot figure out how to initialize a nested struct. Find an example here: http://play.golang.org/p/NL6VXdHrjh
package main
type Configuration struct {
Val string
Proxy struct {
Address string
Port string
}
}
func main() {
c := &Configuration{
Val: "test",
Proxy: {
Address: "addr",
Port: "80",
}
}
}
Go Solutions
Solution 1 - Go
Well, any specific reason to not make Proxy its own struct?
Anyway you have 2 options:
The proper way, simply move proxy to its own struct, for example:
type Configuration struct {
Val string
Proxy Proxy
}
type Proxy struct {
Address string
Port string
}
func main() {
c := &Configuration{
Val: "test",
Proxy: Proxy{
Address: "addr",
Port: "port",
},
}
fmt.Println(c)
fmt.Println(c.Proxy.Address)
}
The less proper and ugly way but still works:
c := &Configuration{
Val: "test",
Proxy: struct {
Address string
Port string
}{
Address: "addr",
Port: "80",
},
}
Solution 2 - Go
If you don't want to go with separate struct definition for nested struct and you don't like second method suggested by @OneOfOne you can use this third method:
package main
import "fmt"
type Configuration struct {
Val string
Proxy struct {
Address string
Port string
}
}
func main() {
c := &Configuration{
Val: "test",
}
c.Proxy.Address = `127.0.0.1`
c.Proxy.Port = `8080`
}
You can check it here: https://play.golang.org/p/WoSYCxzCF2
Solution 3 - Go
Define your Proxy struct separately, outside of Configuration, like this:
type Proxy struct {
Address string
Port string
}
type Configuration struct {
Val string
P Proxy
}
c := &Configuration{
Val: "test",
P: Proxy{
Address: "addr",
Port: "80",
},
}
Solution 4 - Go
You have this option also:
type Configuration struct {
Val string
Proxy
}
type Proxy struct {
Address string
Port string
}
func main() {
c := &Configuration{"test", Proxy{"addr", "port"}}
fmt.Println(c)
}
Solution 5 - Go
One gotcha arises when you want to instantiate a public type defined in an external package and that type embeds other types that are private.
Example:
package animals
type otherProps{
Name string
Width int
}
type Duck{
Weight int
otherProps
}
How do you instantiate a Duck in your own program? Here's the best I could come up with:
package main
import "github.com/someone/animals"
func main(){
var duck animals.Duck
// Can't instantiate a duck with something.Duck{Weight: 2, Name: "Henry"} because `Name` is part of the private type `otherProps`
duck.Weight = 2
duck.Width = 30
duck.Name = "Henry"
}
Solution 6 - Go
You also could allocate using new and initialize all fields by hand
package main
type Configuration struct {
Val string
Proxy struct {
Address string
Port string
}
}
func main() {
c := new(Configuration)
c.Val = "test"
c.Proxy.Address = "addr"
c.Proxy.Port = "80"
}
See in playground: https://play.golang.org/p/sFH_-HawO_M
Solution 7 - Go
You need to redefine the unnamed struct during &Configuration{}
package main
import "fmt"
type Configuration struct {
Val string
Proxy struct {
Address string
Port string
}
}
func main() {
c := &Configuration{
Val: "test",
Proxy: struct {
Address string
Port string
}{
Address: "127.0.0.1",
Port: "8080",
},
}
fmt.Println(c)
}
Solution 8 - Go
You can define a struct and create its object in another struct like i have done below:
package main
import "fmt"
type Address struct {
streetNumber int
streetName string
zipCode int
}
type Person struct {
name string
age int
address Address
}
func main() {
var p Person
p.name = "Vipin"
p.age = 30
p.address = Address{
streetName: "Krishna Pura",
streetNumber: 14,
zipCode: 475110,
}
fmt.Println("Name: ", p.name)
fmt.Println("Age: ", p.age)
fmt.Println("StreetName: ", p.address.streetName)
fmt.Println("StreeNumber: ", p.address.streetNumber)
}
Hope it helped you :)
Solution 9 - Go
package main
type Proxy struct {
Address string
Port string
}
type Configuration struct {
Proxy
Val string
}
func main() {
c := &Configuration{
Val: "test",
Proxy: Proxy {
Address: "addr",
Port: "80",
},
}
}