[Golang] Custom Type Declarations and Struct

Technically, Go is not an object-oriented programming language. It doesn’t have classes, objects, and inheritance. However, you can define custom tyes with methods(receiver functions) as alternative in Go. For exmaple:

decks.go

package main

import "fmt"

// Create a new type of 'deck'
// which is a slice of strings
type decks []string

// 'd' is the copy of the variable of type 'decl'
// that has access to this NewStandardDeck() method
func (d decks) newStandardDeck() decks {
	newDecks := []string{}
	suits := [4]string{"Clubs", "Diamonds", "Hearts", "Spades"}
	ranks := [13]string{"A", "2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K"}

	for _, s := range suits {
		for _, r := range ranks {
			newDecks = append(newDecks, s+" "+r)
		}
	}
	return newDecks
}

func (d decks) print() {

	for _, value := range d {
		fmt.Println(value)
	}
}

main.go

package main

func main() {
	deck := decks{"Test"}
	deck = deck.newStandardDeck()
	deck.print()
}

Struct

A struct is a user-defined type which contains properties that are related together.
For example, we can define a struct Card to reprecent a card in a standard deck.

// Create a new type call Card
type card struct {
	suit string
	rank string
}

// Create a new type of 'deck'
// which is a slice of strings
type decks []card

// 'd' is the copy of the variable of type 'decl'
// that has access to this NewStandardDeck() method
func (d decks) newStandardDeck() decks {
	newDecks := []card{}
	suits := [4]string{"Clubs", "Diamonds", "Hearts", "Spades"}
	ranks := [13]string{"A", "2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K"}

	for _, s := range suits {
		for _, r := range ranks {

			// you can initial card via "card{suit: s, rank: r}" as well
			newDecks = append(newDecks, card{s, r})
		}
	}
	return newDecks
}

func (d decks) print() {
	for _, value := range d {
		fmt.Println(value.suit, value.rank)
	}
}

func (d decks) printWithField() {
	for _, value := range d {
		fmt.Printf("%+v\n", value)
	}
}

We can use struct in a struct as well.

type contactInfo struct {
	phone string
	email string
}

type player struct {
	name    string
	coins   int
	contact contactInfo
}

func main() {
	player1 := player{name: "Brandon", coins: 1000}
	player1.contact = contactInfo{"0987123456", "[email protected]"}

	player2 := player1

	fmt.Printf("%+v\n", player1)
}

Structs Are Pass By Value

When you assign one struct variable to another, a new copy of the struct is created and assigned. For example:

player1 := player{name: "Brandon", coins: 1000}
player1.contact = contactInfo{"0987123456", "[email protected]"}

player2 := player1
player2.name = "Kobe"

fmt.Printf("%s\n", player1.name) // output = Brandon
fmt.Printf("%s\n", player2.name) // output = Kobe

Comparation Between Variables of Same Struct

Because Go does not support overloading of methods and operators, you have to implement function for comparing two variables of same struct.

type contactInfo struct {
	phone string
	email string
}

type player struct {
	name    string
	coins   int
	contact contactInfo
}

func (a player) isRicherThan(b player) bool {
	if a.coins > b.coins {
		return true
	}
	return false
}

func main() {

	player1 := player{name: "Brandon", coins: 5000}
	player2 := player{name: "Mark", coins: 1000}

	if player1.isRicherThan(player2) {
		fmt.Printf("%s has more coins.\n", player1.name)
	}

	if !player2.isRicherThan(player1) {
		fmt.Printf("%s has less coins.\n", player2.name)
	}
}