created a separate file like a class and used in main function and write data on file

deck.go

+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"math/rand"
+	"os"
+	"strings"
+	"time"
+)
+
+// Create a new type of 'deck'
+// which is a slice of strings
+type deck []string
+
+func newDeck() deck {
+	cards := deck{}
+
+	cardSuits := []string{"Spades", "Diamonds", "Hearts", "Clubs"}
+	cardValues := []string{"Ace", "Two", "Three", "Four"}
+
+	for _, suit := range cardSuits {
+		for _, value := range cardValues {
+			cards = append(cards, value+" of "+suit)
+		}
+	}
+
+	return cards
+}
+
+func (d deck) print() {
+	for i, card := range d {
+		fmt.Println(i, card)
+	}
+}
+
+func deal(d deck, handSize int) (deck, deck) {
+	return d[:handSize], d[handSize:]
+}
+
+func (d deck) toString() string {
+	return strings.Join([]string(d), ",")
+}
+
+func (d deck) saveToFile(filename string) error {
+	return ioutil.WriteFile(filename, []byte(d.toString()), 0666)
+}
+
+func newDeckFromFile(filename string) deck {
+	bs, err := ioutil.ReadFile(filename)
+	if err != nil {
+		// Option #1 - log the error and return a call to newDeck()
+		// Option #2 - Log the error and entirely quit the program
+		fmt.Println("Error:", err)
+		os.Exit(1)
+	}
+
+	s := strings.Split(string(bs), ",")
+	return deck(s)
+}
+
+func (d deck) shuffle() {
+	source := rand.NewSource(time.Now().UnixNano())
+	r := rand.New(source)
+
+	for i := range d {
+		newPosition := r.Intn(len(d) - 1)
+
+		d[i], d[newPosition] = d[newPosition], d[i]
+	}
+}

main.go

 package main
 
-import "fmt"
-
-type ShapeCalculator interface {
-	Area() int
-	Perimeter() int
-}
-
-type Rectangle struct {
-	Width  int
-	Height int
-}
-
-func (r *Rectangle) Area() int {
-	return r.Width * r.Height
-}
-
-// func (r *Rectangle) Perimeter() int {
-// 	return r.Width * r.Height
-// }
-
-// uncomment the following line to guarantee that Implementation implements all methods of SomeInterface
-// var _ ShapeCalculator = (*Rectangle)(nil) // ← this is the line
-
 func main() {
-	rect := &Rectangle{
-		Width:  10,
-		Height: 3,
-	}
-	fmt.Println(rect.Area())
+	cards := newDeck()
+	cards.shuffle()
+	cards.print()
 }
+
+// Execute commond both file like : go run main.go deck.go