Course: Learning GO

A collection of go basic fundamentals, syntax and concepts.

Table of contents

Lesson: Type Definitions

Type Definitions

  • New Types
  • Aliases
    // Type Alias
    type distance = float32

    // New type based on 
    type distance float32

    // types have a constructor and conversion functions
    d := distance(34.5)

Methods for a type

type distance float32 // miles
type distanceKm float64

// Method for a type
func (km distanceKm) ToMiles() distance {
	return distance(km / 1.6)

func (miles distance) ToKm() distanceKm {
	return distanceKm(1.6 * miles)

func test() {
	d := distance(4.5)
	// using the type method
	km := d.ToKm()


Complex types for definitions

  • Structures

    • They kind of replace the class idea
    • It’s a data type with strongly typed property
    • They have default contructor
    • You can add methods to it
  • Interfaces

    • A definition of methods
    • You emulate polimorphism from OOP
    • Implicit implementation
    • We can embed interfaces in other interfaces

Type - Structs

If you want to export struct remember to user TitleCase.
You will find two pre-built constructors, with and without name

type User struct{
    id int
    name string

func main(){
    var u2 User
    u1 = User {id:1,name:"Frontend Masters"}
    u2 := User {2,"frontend Masters"}

Type - Struct with Methods

Structs are functions attached to a type declared outside of the structure.

func (u User) PrettyPrint() string {
    return string( + ": " +

func main(){
    u2 := User {2,"Frontend Masters"}
    msg := u2.PrettyPrint()

When embedding struct, we are embedding its methods as well


It’s just a list of methods that then wew can use as a type

type PrettyPrinted interface {
    PrettyPrint() string

func saveObject(object PrettyPrinted){

func main(){
    u2 := User {2, "Frontend Masters"}

WE can embed interfaces

Interface of any thing

var things []interface{}

things = append(things, "34")
things = append(things, 1)
things = append(things, true)

// Casted to type Workshop