Mahesh

Golang Basics

Its just the basics, where I have summed up the syntaxes for writing golang

You atleast should know some programming basics to understand this. It is for my journal, as I would approach myself to learn golang. I have worked in javascript and trying out golang for my learning. And this is how I learn basics before building.

Basic golang main() that prints Hello World 

package main
import (
	"fmt"
)
func main() {
	fmt.Println("Hello World")
}

Variable declarations

package main
import (
	"fmt"
	"strings"
)
func main() {
    
    likes, comments := 1000, 30
	fmt.Println(likes, comments)
	name, age := "Sangram", 30
	fmt.Println(strings.ToUpper(name), age)
	const pName = "Sangram"
	fmt.Println(pName)
}
  • Except pName, all other variables are mutable as pName, is a constant
  • := –> this operator is only applicable inside a function, not outside of it

If Condition

package main
import (
	"fmt"
)
func main() {
    noOfItems := 15
	pricePerItem := 20
    
    if total := noOfItems * pricePerItem; total >= 100 {
		fmt.Println("Free Shipping")
	} else {
		fmt.Println("Apply Shipping Cost")
	}
}

NOTE: total is local to the if condition, as it is not accessible to outside the if-else block

For Loop

package main
import (
	"fmt"
)
func main() {
	for i := 0; i < 5; i++ {
		fmt.Println(i)
	}
}

Arrays/Slices

package main
import (
	"fmt"
)
func main() {
	var arr [3]int
	arr[0] = 1
	arr[1] = 2
	arr[2] = 3
	fmt.Println(arr)
	arr2 := [3]int{5, 6, 7}
	fmt.Println(arr2)
	slice1 := []int{8, 9}
	fmt.Println(slice1)
	slice1[1] = 10
	fmt.Println(slice1)
	// Append to a slice
	var slice2 []int
	slice2 = append(slice2, 11)
	slice2 = append(slice2, 12, 13)
	fmt.Println(slice2)
	// Use make() to create a slice
	slice3 := make([]int, 0, 5)
	fmt.Println(slice3, len(slice3), cap(slice3))
	slice4 := []int{14, 15}
	slice5 := []int{16, 17}
	slice4 = append(slice4, slice5...) // Merge 2 slices
	fmt.Println(slice4)
	sum := 0
	nums := []int{18, 19, 20}
	for i, v := range nums {
		fmt.Println("index", i, "num", v)
		sum += v
	}
	fmt.Println(sum)
}
  • Arrays are fixed in length, we cannot extend it
  • Slices are variable in length and increases in double
  • append() is used to add elements and merge slices
  • make() can be used to create slice
  • slice5…: spread operator to be used to spread the slice so that all the elements of slice5 can be added to slice4
  • range: it can be used to loop through slices

Maps/Objects

package main
import (
	"fmt"
)
func main() {
    
    ages := map[string]int{
		"sangram": 30,
	}
	fmt.Println(ages)
	fmt.Println(ages["sangram"])
	fmt.Println(ages["sangram2"]) // empty key value in map()
	var mapData map[string]int
	mapData = make(map[string]int)
	mapData["sangram"] = 30
	fmt.Println(mapData)
	delete(mapData, "sangram")
	delete(mapData, "sangram2") // no error in map delete
	fmt.Println(mapData)
	mapData2 := make(map[string]int)
	mapData2["rakesh"] = 33
	if _, ok := mapData2["rakesh2"]; ok {
		fmt.Println("We have key value pair")
	} else {
		fmt.Println("We do not have key value pair")
	}
	mapData3 := map[string]int{
		"biscuit": 10,
		"mixture": 100,
	}
	for item, price := range mapData3 {
		fmt.Println("item", item)
		fmt.Println("price", price)
	}
}
  • while deleting a value from the map, if we do not have that then go wont throw an error
  • range can also be used to loop thru map
  • to check for key in the map, we need to explicitly check it, may be a separate function needed to be made for that

Functions

package main
import (
	"fmt"
    "strconv"
)
func main() {
    
    // func inside func
	add := func(a int, b int) int {
		return a + b
	}
	sum2 := add(1, 2)
	fmt.Println(sum2)
	// define and invoke
	add3 := func(a int, b int) int {
		return a + b
	}(1, 2)
	fmt.Println(add3)
	sum3 := add2(3, 4)
	fmt.Println(sum3)
	sumNProduct := func(a, b int) (int, int) {
		return a + b, a * b
	}
	sum4, prod := sumNProduct(5, 6)
	fmt.Println(sum4, prod)
	x, y := namedReturns(3)
	fmt.Println(x, y)
	// variadic function
	sumOfCubes := func(nums ...int) int {
		sum := 0
		for _, num := range nums {
			sum += num * num * num
		}
		return sum
	}
	result2 := sumOfCubes(slice4...)
	fmt.Println(result2)
	parseLevel := func(s string) (int, error) {
		n, err := strconv.Atoi(s)
		if err != nil {
			return 0, fmt.Errorf("level must be a number")
		}
		if n < 1 || n > 5 {
			return 0, fmt.Errorf("level must be between 1 and 5")
		}
		return n, nil
	}
	level, err := parseLevel("30")
	if err != nil {
		fmt.Println("Error while parsing level")
	} else {
		fmt.Println(level)
	}
}
func add2(a, b int) int {
	return a + b
}
// func with named returns
func namedReturns(a int) (sqr int, cube int) {
	sqr = a * a
	cube = a * a * a
	return
}

Defer

Its like cleanup before function ends. Something like return () => {} in useEffect, for React devs

package main
import (
	"fmt"
    "errors"
)
func main() {
    
    // Learn Defer
	learnDefer := func(succes bool) error {
		fmt.Println("start working with resource")
		defer fmt.Println("will always get called before the function ends... cleaning up resources")
		if !succes {
			return errors.New("Error occured")
		}
		fmt.Println("resources work finished")
		return nil
	}
	if err := learnDefer(true); err == nil {
		fmt.Println("No errors")
	}
	if err := learnDefer(false); err != nil {
		fmt.Println("Errors occured")
	}
}

Pointers

package main
import (
	"fmt"
)
func main() {
    
    score := 20
	fmt.Println("score value b4 changing:", score)
	changeScore := func(score *int) {
		*score += 5
	}
	changeScore(&score)
	fmt.Println("score avlue after changing w/pointer:", score)
	changeScore2 := func(score int) {
		score += 5
	}
	changeScore2(score)
	fmt.Println("score value after changing w/o pointer:", score)
	user := User{FirstName: "Sangram", MiddleName: "", LastName: "Mohanty", Age: 30}
	fmt.Println("b4 Age normal receiver:", user.Age)
	// struct reciever normal
	fmt.Println(user.FullName())
	fmt.Println("after Age normal receiver:", user.Age)
	// struct reciever pointer
	fmt.Println(user.HappyBirthday())
	fmt.Println("after Age pointer receiver:", user.Age)
}
type User struct {
	FirstName  string
	MiddleName string
	LastName   string
	Age        int
}
func (u User) FullName() string {
	u.Age++
	return fmt.Sprintf("Hi, my name is %s", u.FirstName+" "+u.MiddleName+" "+u.LastName)
}
func (u *User) HappyBirthday() string {
	u.Age++
	return fmt.Sprintf("Hi, my name is %s", u.FirstName+" "+u.MiddleName+" "+u.LastName)
}
  • We can add functionality/methods to struct
  • We can change the value of the pointers by passing its reference
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