structs.md

Structs

A struct can be used to implement a structured data type.

When you have defined your struct, for example like this person structure:

type person struct {
    name string
    age  int
}

You can initialize it easily like so:

fmt.Println(person{"Bob", 20})

If you however change your struct or reorder the fields, for example to be alphabetical:

type person struct {
    age  int
    name string
}

The short-form for initialization will render unexpected results.

So it is recommended to use long-form:

fmt.Println(person{name: "Alice", age: 30})

This does not get influence by reordering the fields or the addition of new fields, the latter since non-specified fields will simply be set to the defaults:

• 0 for numbers, meaning 0 for integers and 0.000000 for floats
• empty string ("") for strings
• false for booleans

type person struct {
    age  int
    name string
    height float32
}

Here follows a more complete example:

package main

import "fmt"

type person struct {
    age    int
    name   string
    height float32
    parent bool
}

func main() {
    p := person{}

    fmt.Printf("height of >%s<: >%f< aged >%d< and parent: >%t<\n", p.name, p.height, p.age, p.parent)
}

zsh> go build -o default default.go
zsh> ./default
height of ><: >0.000000< aged >0< and parent: >false<

Making structs pretty for printing is easy:

package main

import "fmt"

type User struct {
    FirstName string
    LastName  string
}

func (u User) String() string {
    return fmt.Sprintf("First name: %s\nLast name: %s\n", u.FirstName, u.LastName)
}

func main() {
    me := User{
        FirstName: "Jonas",
        LastName:  "Brømsø",
    }
    fmt.Printf("%s\n", me)
}

The suggestion for the String interface came from the good people from the Gopher Slack.

Resources and References

1. Go By Example: structs
2. Yourbasic Go: fmt.Printf formatting tutorial and cheat sheet
3. Stackoverflow: "unknown field in struct literal"