https://github.com/foyez/go
Golang at a glance
https://github.com/foyez/go
go golang
Last synced: about 2 months ago
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Golang at a glance
- Host: GitHub
- URL: https://github.com/foyez/go
- Owner: foyez
- Created: 2021-08-01T05:26:19.000Z (almost 4 years ago)
- Default Branch: main
- Last Pushed: 2025-02-24T16:46:30.000Z (4 months ago)
- Last Synced: 2025-03-29T22:43:00.039Z (2 months ago)
- Topics: go, golang
- Language: Go
- Homepage:
- Size: 262 KB
- Stars: 3
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
Awesome Lists containing this project
README
# Golang
**[Go Playground](https://play.golang.org/)**
- Programming Language developed by Google in 2007
- Open-sourced in 2009
## Why Go
View contents
1. Strongly type language (Variable type has to be known at compile time)
2. Statically type language (The type of the variables cannot change at runtime)
3. Nearly as fast as C and C++
4. Readable as Python
5. Fast execution
6. Automatic garbage collection
7. Run on multiple cores and builtin to support concurrency
- **In Parallel:** Downloading, Uploading, Navigating at the same time
- **Multi-Threading:** Do multiple things at once, e.g., Watching, commenting in Youtube
- **Concurrency:** Dealing with lots of things at once but not necessarily run at the same time, e.g., Multiple users booking at the same time, Multiple users editing the same document
## Go vs JS
View contents
1. TYPING
- Go: Strongly typed (String, Float, Int, Byte, Struct...)
- JS: Dynamically typed
2. STRUCTURES
- Go: Structs, Pointers, Methods, Interfaces
- JS: ES6 classes
3. ERROR HANDLING
- Go: Explicit (sad path won't handle itself)
- JS: Built-in
4. MULTI-TASKING
- Go: Multi-Threaded (Concurrency, Goroutines, Sync)
- JS: Single-Threaded (Callbacks, async await, sagas, sadness)
5. OPINIONATED-NESS
- Go: Strong Opinions (Convention, built-in tooling and linters)
- JS: Fluid Opinions (Subjective to the mood that day)
## Setup go
View contents
1. Download go installer & install it. link: [go installer](https://go.dev/doc/install)
2. Add environment variables into shell config
Bash shell
```bash
# ~/.bash_profile
# set the workspace path
export GOPATH=$HOME/go-workspace # change your path correctly!
# add the go bin path to be able to execute our programs
export PATH=$PATH:$GOPATH/bin
```
Fish shell
```bash
# ~/.config/fish/config.fish
# set the workspace path
set -x GOPATH $HOME/go-workspace # change your path correctly!
# add the go bin path to be able to execute our programs
set -x PATH $PATH /usr/local/go/bin $GOPATH/bin
```
3. Create workspace
```bash
$ mkdir -p $GOPATH $GOPATH/src $GOPATH/pkg $GOPATH/bin
# $GOPATH/src : Where your Go projects / programs are located
# $GOPATH/pkg : contains every package objects
# $GOPATH/bin : The compiled binaries home
```
4. Install godoc & run godoc
```bash
$ go install golang.org/x/tools/cmd/godoc@latest
# run godoc
$ godoc -http :8000
# go to: localhost:8000/pkg
# go to personal project: localhost:8000/pkg/project-name
```
5. Update the Go version
```sh
# Uninstall the exisiting version
$ sudo rm -rf /usr/local/go
```
Download the latest go installer & install it. Link:
7. VS Code Setup
`settings.json`
```json
{
"[go]": {
"editor.quickSuggestions": {
"other": "off",
"comments": "off",
"strings": "off"
}
},
"go.toolsManagement.autoUpdate": true,
"go.testFlags": ["-v", "-count=1"],
"protoc": {
"options": ["--proto_path=proto"]
}
}
```
- Install `[Go](https://marketplace.visualstudio.com/items?itemName=golang.go)` extension
- Install `[vscode-proto3](https://marketplace.visualstudio.com/items?itemName=zxh404.vscode-proto3)` extension for **gRPC**
## Go Directory Structure
View contents
```txt
$GOPATH
│
└───bin
│
└───pkg
│
└───src
│
│
└───github.com
│
└───github_username
│
└───repo_name
```
## Create a go project
View contents
```bash
# created a directory called "hello"
$ mkdir hello
# change directory to "hello
$ cd hello
# create "main.go" file
$ touch main.go
# generate "go.mod" file
$ go mod init github.com/foyez/hello # module path can be repository you want to publish
```
`go.mod`
```go
module github.com/foyez/hello // name or module path
go 1.18 // go version
```
## Anatomy of a go file
View contents
`main.go`
```go
// package name
/*
Every go program needs at least one package main
Go programs are organized into packages
A package is a collection of source files
*/
package main
import (
"fmt" // import built-in packages
"github.com/foyez/hello/utils" // import custom packages
)
// Every go program needs one main function
// It's the entry point for the program where
// go starts executing the code
func main() {
fmt.Println("Hello, World")
fmt.Print(utils.Add(10, 20))
}
```
`utils/utils.go`
```go
package utils
// private variable - start with lowercase
// Can't be accessed from other packages
var s = "Hello"
// Public function - starting with capital letter
// Can be accessed from other packages
func Add(a int64, b int64) int64 {
return a + b
}
```
- compiles and runs the code: `go run `
- build the code: `go build main.go`
## Go Commands
View contents
```sh
# run a go program
$ go run main.go # go run
# install go packages
$ go install
# create a binary file from go codes
$ go build
# format unindent go code
$ go fmt main.go
# shows go package directory tree
$ go list
# identify unused variables & errors
$ go vet
# show go documentation
go doc fmt.Println
# install third party library
$ go get golang.org/x/lint/golint
# linting go code
golint
```
## List of keywords
View contents
The list of all **25** keywords of Go language:
1. `break`
2. `case`
3. `chan`
4. `const`
5. `continue`
6. `default`
7. `defer`
8. `else`
9. `fallthrough`
10. `for`
11. `func`
12. `go`
13. `goto`
14. `if`
15. `import`
16. `interface`
17. `map`
18. `package`
19. `range`
20. `return`
21. `select`
22. `struct`
23. `switch`
24. `type`
25. `var`
## TDD with Go
View contents
**[You can find all the code for this section here](https://github.com/foyez/go/tree/main/codes/tddWithGo)**
1 **Write the test first**
`hello_test.go`
```go
package hello
import "testing"
// exported if it begins with a capital letter
func TestHello(t *testing.T) {
t.Run("saying hello to people", func(t *testing.T) {
got := Hello("Foyez")
want := "Hello, Foyez"
if got != want {
t.Errorf("got %q want %q", got, want)
}
})
}
```
run `go test`
```sh
./hello_test.go:7:10: undefined: Hello
```
2. **Write the minimal amount of code for the test to run and check the failing test output**
```go
package hello
func Hello(name string) string {
return ""
}
```
run `go test`
```sh
hello_test.go:11: got "" want "Hello, Foyez"
```
3. **Write enough code to make it pass**
```go
func Hello(name string) string {
return "Hello, " + name
}
```
run `go test`
```
PASS
ok hello 0.004s
```
4. **Commit the code**
```git
git commit "add Hello() - greeting to people"
```
5. **Refactor**
`hello.go`
```go
package hello
const englishHelloPrefix = "Hello, "
func Hello(name string) string {
return englishHelloPrefix + name
}
```
`hello_test.go`
```go
package hello
import "testing"
func TestHello(t *testing.T) {
assertErrorMessage := func(t testing.TB, got, want string) {
t.Helper()
if got != want {
t.Errorf("got %q want %q", got, want)
}
}
t.Run("saying hello to people", func(t *testing.T) {
got := Hello("Foyez")
want := "Hello, Foyez"
assertErrorMessage(t, got, want)
})
}
```
run `go test`
```sh
PASS
ok hello 0.004s
```
6. **Amend git commit**
```git
git commit --amend
```
#### TDD workflow
- Write a test
- Make the compiler pass
- Run the test, see that it fails and check the error message is meaningful
- Write enough code to make the test pass
- Refactor
7. **Add Benchmark test**
```go
func BenchmarkHello(b *testing.B) {
if testing.Short() {
b.Skip("skipping benchmark in short mode.")
}
for i := 0; i < b.N; i++ {
Hello("Zayan")
}
}
```
run `go test -v --bench . --benchmem`
```sh
BenchmarkHello 2000000000 0.46 ns/op
// This means that the loop ran 2000000000 times at a speed of 0.46 ns per loop.
```
8. **Add example tests**
```go
func ExampleHello() {
greeting := Hello("Zayan")
fmt.Println(greeting)
// Output: Hello, Zayan
}
func ExampleHello() {
greeting := Hello("Farah")
fmt.Println(greeting)
// Output: Hello, Farah
}
```
run `go test -v`
```sh
=== RUN TestHello
=== RUN TestHello/saying_hello_to_people
--- PASS: TestHello (0.00s)
--- PASS: TestHello/saying_hello_to_people (0.00s)
=== RUN ExampleHello
--- PASS: ExampleHello (0.00s)
=== RUN ExampleHello_second
--- PASS: ExampleHello_second (0.00s)
```
## Printing and Getting user input
View contents
**[You can find all the code for this section here](https://github.com/foyez/go/tree/main/codes/printing)**
### **Print**
```go
fmt.Print()
fmt.Println()
fmt.Printf()
```
- Prints output to the stdout console
- Returns number of bytes and an error
- (The error is generally not worried about)
```go
name := "Zohan"
fmt.Print("Hello, ", name, "\n")
fmt.Println("Hello,", name)
fmt.Printf("Hello, %s\n", name)
```
```go
s := Student{
ID: 1,
Name: "John Doe",
}
fmt.Printf("%s\n", "Hello") // string
fmt.Printf("%d\n", -34) // decimal
fmt.Printf("%+d\n", 4) // positive decimal
fmt.Printf("%t\n", false) // boolean
fmt.Printf("%f, %.2f\n", 3.1416, 3.1416) // float
fmt.Printf("%v\n", s)
fmt.Printf("%+v\n", s)
fmt.Printf("%T\n", s)
```
### Fprint
```go
fmt.Fprint()
fmt.Fprintln()
fmt.Fprintf()
```
- Prints the output to an external source (not in stdout console) (file, browser)
- Returns number of bytes, and any write error
### Sprint
```go
fmt.Sprint()
fmt.Sprintln()
fmt.Sprintf()
```
- Stores output on a character buffer
- Doesn't print to stdout console
- Returns the string
### Scan
```go
fmt.Scan()
fmt.Scanln()
fmt.Scanf()
```
- Read input from the stdout console
- Returns number of bytes and an error
- (The error is generally not worried about)
```go
var name string
fmt.Scan("Hello, ", &name)
fmt.Println("Hello,", name)
fmt.Scanf("Hello, %s", &name)
fmt.Println("Hello,", name)
fmt.Scanln("Hello, ", &name)
fmt.Println("Hello,", name)
```
### `os.Args`
- Read input from command-line
- User input starts from 1st index
```go
import (
os
)
arguments := os.Args
```
```sh
go run main.go 10 20
# argouments[1] -> 10
# argouments[2] -> 20
```
## Types
View contents
**[You can find all the code for this section here](https://github.com/foyez/go/tree/main/codes/types)**
| Name | Type Name | Examples |
| ----------- | --------------------------------------------------------------------------- | ----------------------------------------- |
| **INTEGER** | int, int8, int16, int32, int64
unint, unint8, unint16, unint32, unint64 | var age int = 20
var count unint = -5 |
| **FLOAT** | float32, float64 | var gpa float64 = 3.4 |
| **STRING** | string | var fruit string = "mango" |
| **BOOLEAN** | bool
&& || ! < <= > >= == != | true false
var adult bool = age > 18 |
### Identify and convert type
```go
// identify type
reflect.TypeOf(6) // int
// convert type
float(10) + 5.5 // 15.5
```
## Variables
View contents
**[You can find all the code for this section here](https://github.com/foyez/go/tree/main/codes/variables)**
```go
package main
import "fmt"
// var variableName type = value
// can declare outside and inside of a function
var name string = "Zayan"
func main() {
// Infer variable type
var age = 20
// variables without assigning value
// return default value
// int: 0, float: 0.0, string: "", bool: false
var salary int
// value cannot be changed/re-assigned
const birthPlace = "Bangladesh"
// variables in only function
funcVar := "can't declare outside of a function"
// multiple variables
one, two := 1, "two"
fmt.Println(name, age, salary)
fmt.Println(birthPlace)
fmt.Println(funcVar)
fmt.Println(one, two)
}
```
## Control Structures: If & Else
View contents
**[You can find all the code for this section here](https://github.com/foyez/go/tree/main/codes/control)**
```go
package main
import (
"fmt"
)
func main() {
var age = 10
if age < 18 {
fmt.Println("younger")
} else if age == 18 {
fmt.Println("adult")
} else {
fmt.Println("elder")
}
if name := "Farah"; name != "Farhan" {
fmt.Println("She is Farah")
}
}
```
## Control Structures: switch
View contents
**[You can find all the code for this section here](https://github.com/foyez/go/tree/main/codes/control)**
```go
package main
import "fmt"
func main() {
// *****************************************
switch city := "Cumilla"; city {
case "Dhaka", "Cumilla", "Sylhet":
fmt.Println("You live in", city)
default:
fmt.Println("You're not from around here")
}
// *****************************************
var age int = 30
switch {
case age < 18:
fmt.Println("young")
case age > 18 && age <= 40:
fmt.Println("adult")
default:
fmt.Println("elder")
}
// *****************************************
var num int = 9
switch {
case num != 10:
fmt.Println("Does not equal 10")
fallthrough // check other case after matching this case
case num < 10:
fmt.Println("Less than 10")
case num > 10:
fmt.Println("Greater than 10")
default:
fmt.Println("Is 10")
}
}
```
## Loops
View contents
**[You can find all the code for this section here](https://github.com/foyez/go/tree/main/codes/loops)**
```go
package main
import (
"fmt"
)
func main() {
// *****************************************
// BASIC FOR LOOP
// *****************************************
fmt.Println("Basic for loop")
for i := 1; i <= 5; i++ {
fmt.Print(i)
}
// *****************************************
// SIMILAR TO WHILE LOOP
// *****************************************
fmt.Println("\nSimilar to while loop")
j := 1
for j <= 5 {
fmt.Print(j)
j++
}
// *****************************************
// INFINITE LOOP
// *****************************************
fmt.Println("\nInfinite loop")
num := 1
for {
num = num + 2
if num == 7 {
continue
}
fmt.Print(num)
if num == 11 {
break
}
}
// ********************************************
// BASIC FOR LOOP ITERATION (STRING, ARRAY,...)
// ********************************************
fmt.Println("\nBasic for loop iteration")
var name = "Farah"
for i := 0; i < len(name); i++ {
fmt.Println("Letter:", string(name[i]))
}
// *****************************************
// STRING ITERATION
// *****************************************
fmt.Println("\nString iteration")
var myCity = "কুমিল্লা"
for index, letter := range myCity {
if index % 2 == 0 {
fmt.Printf("Index: %d, Letter:%#U\n", index, letter)
}
}
// *****************************************
// SLICE OR ARRAY ITERATION
// *****************************************
fmt.Println("\nSlice or Array iteration")
cities := []string{"Dhaka", "Cumilla"}
for _, city := range cities {
fmt.Printf("%s ", city)
}
// *****************************************
// MAP ITERATION
// *****************************************
fmt.Println("\nMap iteration")
results := map[string]float64{
"Farah": 3.4,
"Laaibah": 3.3,
"Zayan": 3.5,
}
for key, value := range results {
fmt.Println(key, value)
}
// *****************************************
// CHANNEL ITERATION
// *****************************************
fmt.Println("\nChannel iteration")
ch := make(chan int)
go func() {
ch <- 1
ch <- 2
close(ch)
}()
for n := range ch {
fmt.Println(n)
}
}
```
_[Loop guide](https://yourbasic.org/golang/for-loop-range-array-slice-map-channel/)_
## Functions
View contents
**[You can find all the code for this section here](https://github.com/foyez/go/tree/main/codes/funtions)**
- Basic function
```go
func printAge() {
fmt.Println(10)
}
```
- return type declaration
```go
func printAge(age int) int {
return age
}
```
- return multiple values
```go
func printAge(age int) (string, int) {
return "name", age
}
func main() {
name, age = printAge(10)
}
```
- return named values
```go
func printAge(age1, age2 int) (ageOfBob, ageOfSally int) {
ageOfBob = age1
ageOfSally = age2
return
}
```
- unknown number of arguments / variadic function
```go
func average(ages ...int) float64 {
total := 0
// ages - treated as slice
for _, age := range ages {
total += age
}
return float64(total) / float64(len(ages))
}
func main() {
fmt.Println(average(10, 20, 32))
nums := []int{10, 20, 32}
// unpack or spread
fmt.Println(average(nums...))
}
```
- go functions are `lexically scoped` means variables are accessible from the functions in the same block where the functions are defined
```go
var n1 = 5
func foo(n2 int) {
n3 := 8
fmt.Println(n1, n2, n3)
}
```
- function as first-class value (assigning as variable, pass as argument, return as value, etc.)
```go
func print(n int, fn func(int)) {
fn(n)
}
print(6, func(val int) {
fmt.Println(val) // 6
})
```
```go
func add(n1 int) func(int) int {
fn := func(n2 int) int {
return n1 + n2
}
return fn
}
// n1 is in the closure of fn()
sum := add(1)
fmt.Println(sum(5)) // 6
fmt.Println(sum(2)) // 3
```
When functions are passed/returned, their environment comes with them.
## Arrays
View contents
**[You can find all the code for this section here](https://github.com/foyez/go/tree/main/codes/arrays)**
```go
// ARRAY
// [number]T
// A slice type has a specific length
// declare array
var arr [3]float64
fmt.Println(arr) // [0 0 0]
arr[1] = 23 // set element
element := arr[1] // read element
fmt.Println(arr, element) // [0 23 0] 23
// declare and initialize
scores := [3]float64{9, 1.5, 2.2}
fmt.Println(scores)
// compiler figure out array length
arrNotMax := [...]int{2, 3, 4}
fmt.Println(arrNotMax, len(arrNotMax)) // [2 3 4] 3
// slice
fruits := [5]string{"banana", "pear", "apple", "orange", "peach"}
splicedFruits := fruits[1:3] // [pear apple]
splicedFruits2 := fruits[2:] // [apple orange peach]
removeLastFruit := fruits[:len(fruits)-1] // [banana pear apple orange]
lastFruit := fruits[len(fruits)-1] // peach
fmt.Println(splicedFruits, splicedFruits2, removeLastFruit, lastFruit)
fmt.Println(len(splicedFruits)) // 2
fmt.Println(cap(splicedFruits)) // 4 (since starts from 1 and end index is 4)
// append
fruitsToAdd := append(splicedFruits, "cherry", "pineapple", "guava")
fmt.Println(splicedFruits, fruitsToAdd) // [pear apple] [pear apple cherry pineapple guava]
fmt.Println(len(splicedFruits), cap(splicedFruits)) // 2 4
fmt.Println(len(fruitsToAdd), cap(fruitsToAdd)) // 5 8 (after crossing the previous capacity, the current capcity is doubled up)
// prepend
nums := []int{1,2,3}
nums = append([]int{0}, nums...)
// multidimensional array
multi := [2][3]int{{1, 2, 3}, {5, 6, 7}}
fmt.Println(multi) // [[1 2 3] [5 6 7]]
```
## Slices
View contents
**[You can find all the code for this section here](https://github.com/foyez/go/tree/main/codes/slices)**
```go
// SLICE
// []T
// A slice type has no specific length
// declare a slice
var mySlice []int
fmt.Println(mySlice) // []
// mySlice[0] = 1 // occurs an error, since size is unknown
```
A slice has 3 properties:
- `ptr` - a pointer to the underlying array
- `len` - length of the slice - number of elements in the slice
- `cap` - capacity of the slice - length of the underlying array, which is also the maximum length the slice can take (until it grows)
source: https://gosamples.dev/capacity-and-length/
When we copy a slice it creates a new memeory location where it holds the same memory address of the underlying array, length & capacity. That's why, when modify the new copy of the slice, it also modify the old slice.
```go
var s = []int{1, 2, 3}
var s2 = s
s2[0] = 5
fmt.Println(s, s2) // [5 2 3], [5 2 3]
```
**Make**: make function "Initializes and allocates space in memory for a `slice`, `map`, or `channel`."
```go
// make([]T, len, cap)
s := make([]int, 0, 3)
sliceWithMake[0] = 1
fmt.Println(sliceWithMake) // [1 0 0]
for i := 0; i < 5; i++ {
s = append(s, i)
fmt.Printf("cap %v, len %v, %p\n", cap(s), len(s), s)
}
```
```sh
cap 3, len 1, 0xc0000b2000
cap 3, len 2, 0xc0000b2000
cap 3, len 3, 0xc0000b2000
cap 6, len 4, 0xc0000b8000 # larger capacity and a new pointer address
cap 6, len 5, 0xc0000b8000
```
- unpack/spread a slice
```go
var fruits = []string{"apple", "mango"}
// variable argument/vardiac function
func addFruits(fruitsToAdd ...string) []string {
// unpack or spread
updatedFruits := append(fruits, fruitsToAdd...)
return updatedFruits
}
addFruits("banana", "pineapple") // [apple mango banana pineapple]
```
## Maps / Object / Dictionary
View contents
**[You can find all the code for this section here](https://github.com/foyez/go/tree/main/codes/maps)**
1. Map operations
View codes
```go
var results map[string]float64 = make(map[string]float64) // create empty map
fmt.Println(results["test]) // 0
results["foyez"] = 3.4
results["mithu"] = 3.5
fmt.Println(results) // map[foyez:3.4 mithu:3.5]
// ***********************************************
userEmails := map[int]string{
1: "[email protected]",
2: "[email protected]",
}
userEmails[1] = "[email protected]"
emailOfSecondUser, ok := userEmails[2]
emailOfFourthUser, ok2 := userEmails[4]
fmt.Println(userEmails) // map[1:[email protected] 2:[email protected]]
fmt.Println(emailOfSecondUser, ok) // [email protected] true
fmt.Println(emailOfFourthUser, ok2) // false
if email, ok := userEmails[2]; ok {
fmt.Printf("%s exists\n", email)
} else {
fmt.Printf("%s doesn't exists\n", email)
}
delete(userEmails, 1)
fmt.Println(userEmails) // [2:[email protected]]
```
2. Iterating map
View codes
```go
users := map[string]interface{}{
"name": "zayan",
"age": 5,
"religion": "islam",
}
for key, val := range users {
fmt.Printf("%s -> %v\n", key, val) // name -> zayan, age -> 5, religion -> islam
}
```
## Strings
View contents
**[You can find all the code for this section here](https://github.com/foyez/go/tree/main/codes/strings)**
```go
package main
import (
"fmt"
s "strings"
)
var p = fmt.Println
func main() {
p(s.Contains("test", "es")) // true
p(s.Count("test", "t")) // 2
p(s.HasPrefix("test", "te")) // true
p(s.HasSuffix("test", "st")) // true
p(s.Index("test", "t")) // 0
p(s.LastIndex("test", "t")) // 3
p(s.Join([]string{"a", "b"}, "-")) // a-b
p(s.Repeat("a", 5)) // aaaaa
p(s.Replace("fooo", "o", "O", -1)) // fOOO
p(s.Replace("fooo", "o", "O", 2)) // fOOo
p(s.Split("a-b-c", "-")) // [a b c]
p(s.ToLower("TEST")) // test
p(s.ToUpper("test")) // TEST
p(len("hello")) // 5
p("hello"[1]) // 1
}
```
## Structs
View contents
**[You can find all the code for this section here](https://github.com/foyez/go/tree/main/codes/structs)**
```go
type User struct {
ID int
FirstName string
LastName string
Email string
}
user := User{ID: 1, FirstName: "Foyez", LastName: "Ahmed", Email: "[email protected]"}
fmt.Println(user.FirstName) // Foyez
```
## Pointers
View contents
**[You can find all the code for this section here](https://github.com/foyez/go/tree/main/codes/pointers)**
**Pointer:** a variable that holds the **memory location** of a variable instead of a copy of its value.
```go
// Declare a pointer variable
var variableName *type
// Access to the variable address
&variableName
// Access to the variable value
*variableName
```
```go
type person struct {
firstName string
lastName string
faboriteSports []string
}
func main() {
person := person{
firstName: "Foyez",
lastName: "Ahmed",
faboriteSports: []string{"Cricket"}
}
updateFirstName(&person, "Rumon")
fmt.Println(person) // {Foyez Ahmed [Cricket]}
updateFavoriteSports(person, "Football")
fmt.Println(person) // {Foyez Ahmed [Football]}
}
func updateFirstName(p *person, newFirstName string) {
fmt.Println(p) // &{Foyez Ahmed [Cricket]}
fmt.Println(&p) // 0xc00000e028
fmt.Println(*p) // {Foyez Ahmed [Cricket]}
// (*p).firstName = newFirstName
p.firstName = newFirstName
}
func updateFavoriteSports(p person, sportName string) {
p.favoriteSports[0] = sportName
}
```
**Value Types:** `int`, `float`, `string`, `bool`, `structs`, `array`
> Have to use pointer to update these types of variables
**Reference Types:** `slices`, `maps`, `channels`, `pointers`, `functions`
> Don't need to use pointer to update these types of variables
**Call by Value:**
- Passed arguments or receiver are copied to parameters
- Modifying parameters or receiver has no effect outside of the function or the method
```go
type Person struct {
name string
age int
}
func updateAge(p Person) {
p.age = 20
fmt.Println(p) // {Mithu 20}
}
func (p Person) updateAge() {
p.age = 30
fmt.Println(p) // {Mithu 30}
}
func main() {
mithu := Person{name: "Mithu", age: 10}
updateAge(mithu)
fmt.Println(mithu) // {Mithu 10}
mithu.updateAge()
fmt.Println(mithu) // {Mithu 10}
}
```
**Call by Reference:**
- Pass pointer (memory location) as arguments or receiver
- Modifying parameters or receiver has effect outside of the function or the method
```go
type Person struct {
name string
age int
}
func updateAge(p *Person) {
p.age = 20
fmt.Println(*p) // {Mithu 20}
}
func (p *Person) updateAge() {
p.age = 30
fmt.Println(*p) // {Mithu 30}
}
func main() {
mithu := Person{name: "Mithu", age: 10}
updateAge(&mithu)
fmt.Println(mithu) // {Mithu 20}
mithu.updateAge()
fmt.Println(mithu) // {Mithu 30}
}
```
## Error Handling
View contents
**[You can find all the code for this section here](https://github.com/foyez/go/tree/main/codes/errors)**
#### Error
- indicates that something bad happened, but it might be possible to continue running the program.
- i.e: A function that intentionally returns an error if something goes wrong
#### Panic
- happen at run time
- something happened that was fatal to the program and program stops execution
- ex: Trying to open a file that doesn't exist
```go
type error interface {
Error() string
}
err := funcReturnError()
fmt.Println(err.Error())
panic(err.Error())
```
#### Defer
A defer statement defers the execution of a function until the surrounding function completes. Typically used for cleanup activities. Arguments of a deffered call are evaluted immediately.
```go
func main(){
let country := "Bangladesh"
defer fmt.Println(country)
defer fmt.Println("love")
country = "Australia"
fmt.Println("I")
}
// I
// love
// Bangladesh
```
#### Recover
- **Panic** is called during a run time error and fatally kill the program
- **Recover** tells Go what to do when a panic happens (returns what was passed to panic)
- Recover must be paired with **defer**, which will fire even after a panic
```go
func recoverFromPanic() {
if r := recover(); r != nil {
fmt.Println(r)
}
}
func main() {
defer recoverFromPanic()
for i := 0; i < 5; i++ {
fmt.Println(i)
if i == 2 {
panic("PANIC!")
}
}
}
// 0
// 1
// 2
// PANIC!
```
## Methods
View contents
**[You can find all the code for this section here](https://github.com/foyez/go/tree/main/codes/methods)**
Syntax of method
```go
func (r ReceiverType) funcName(parameters) (results)
```
#### Methods vs Functions
- The difference between a method and a function is that instead of accepting an argument as struct, we're calling a method on an instance of that struct.
```go
type address struct {
email string
zipCode int
}
type User struct {
name string
age int
address
}
func main() {
user := User{
name: "Manam",
age: 25,
address: address{
email: "[email protected]",
zipCode: 34000
},
}
updateUserName(&user, "Chayon")
// (&user).UpdateName("Chayon")
user.UpdateName("Chayon")
}
func updateUserName(u *User, name string) {
u.name = name
}
// func (receiverName ReceiverType) MethodName(args)
// When a method is called on a variable of that type,
// we get the reference to its data via the receiverName variable.
func (u *User) UpdateName(name string) {
// (*u).name = name
u.name = name
}
```
**When should we make the pointer receiver type of a method?**
1. When the receiver type uses a large amount of memory, otherwise the receiver will be copied with a large amount of data which is costly.
2. When the method must modify the data in the object of the receiver type.
**Good practices:**
1. All methods of a type should have pointer receivers, or
2. All methods of a type should have non-pointer receivers
## Type Assertions
View contents
> Type assertions is used to assert the type of a given variable. It provides access to an interface value's underlying concrete value.
```go
// assertedVariable, ok := variable.(Type)
var foo interface{} = "Hello"
str := foo.(string)
fmt.Println(str) // "Hello"
num := foo.(int) // panic
fmt.Println(num)
num2, ok := foo.(int)
fmt.Println(num2, ok) // 0, false
```
## Interfaces
View contents
**[You can find all the code for this section here](https://github.com/foyez/go/tree/main/codes/interfaces)**
**Structs:** define a set of attributes on a type, e.g.: a user has a `FirstName` and a `LastName`, it is the type of User.
**Interfaces:** define a set of method signatures (name, parameters & return types), NOT the implementation.
```go
type Shape2D interface {
Area() float64
Perimeter() float64
}
type Rectangle struct {
Width float64
Height float64
}
func (r Rectangle) Area() float64 {
return r.Width * r.Height
}
func (r Rectangle) Perimeter() float64 {
return 2 * (r.Width + r.Height)
}
type Circle struct {
Radius float64
}
func (c Circle) Area() float64 {
return math.Pi * c.Radius * c.Radius
}
func (c Circle) Perimeter() float64 {
return 2 * math.Pi * c.Radius
}
func fitInYard(s Shape2D) bool {
return s.Area() > 200 && s.Perimeter() > 200
}
func printShapeProps(s Shape2D) {
if rect, ok := s.(Rectangle); ok {
fmt.Printf("Height: %.2f, Width: %.2f\n", rect.Height, rect.Width)
}
if circle, ok := s.(Circle); ok {
fmt.Printf("Radius: %.2f\n", circle.Radius)
}
}
func main() {
circle := Circle{10}
rectangle := Rectangle{10, 20}
fmt.Println(fitInYard(circle))
fmt.Println(fitInYard(rectangle))
printShapeProps(rectangle) // Height: 20.00, Width: 10.00
printShapeProps(circle) // Radius: 10.00
}
```
#### Empty Interface
```go
interface{}
```
- Specifies zero methods
- An empty interface may hold values of any type
- Like _any_ type in Typescript
```go
var people map[string]interface{} = make(map[string]interface{})
people["name"] = "Foyez"
people["age"] = 28
fmt.Printf("%#v %T\n", people["name"], people["name"]) // "Foyez" string
fmt.Printf("%#v %T", people["age"], people["age"]) // 28 int
```
## Generics
View contents
Suppose, we write a function that accepts string or integer as arguments
```go
func isEqual(a, b interface{}) bool {
return a == b
}
func main() {
fmt.Println(isEqual(1, 1)) // true
fmt.Println(isEqual(1, "1")) // true
}
```
Here, though the empty interface `interface{}` gives us the flexibility to pass string or integer type, it don't provide us type-safety. Because we can't compare a number with a string. This means the compiler can't help us and we're instead more likely to have runtime errors.
To solve this issue, we can use generics which give us flexibility and type-safety at the same time.
```go
func isEqual[T comparable](a, b T) bool {
return a == b
}
func main() {
fmt.Println(isEqual(1, 1)) // true
fmt.Println(isEqual(1, "1")) // default type string of "1" does not match inferred type int for T
}
```
> `comparable` is a built-in Go constraint introduced in Go 1.18. It is used to denote types that can be compared for equality using == and !=.
```go
import (
"fmt"
"golang.org/x/exp/constraints"
)
// Max returns the maximum of two values that implement the Ordered constraint.
func Max[T constraints.Ordered](a, b T) T {
if a > b {
return a
}
return b
}
```
> The `constraints.Ordered` constraint comes from the `golang.org/x/exp/constraints` package and is used to denote types that support ordering operations like <, <=, >, and >=.
**Implementation of `reduce()`, `find()`, `filter()` & `map()`:**
```go
func Reduce[A, B any](collection []A, accumulator func(B, A) B, initialValue B) B {
var result = initialValue
for _, x := range collection {
result = accumulator(result, x)
}
return result
}
func Find[A any](items []A, predict func(A) bool) (value A, found bool) {
for _, v := range items {
if predict(v) {
return v, true
}
}
return
}
func Filter[A any](items []A, predict func(A) bool) []A {
var founds []A
for _, v := range items {
if predict(v) {
founds = append(founds, v)
}
}
return founds
}
func Map[A, B any](items []A, modify func(A) B) []B {
var modifiedItems []B
for _, v := range items {
modifiedItems = append(modifiedItems, modify(v))
}
return modifiedItems
}
```
Reference: [Golang Generics Are Here! - Golang Beyond the Basics](https://www.youtube.com/watch?v=P2CQWeZZ--4)
## Concurrency
View contents
**[You can find all the code for this section here](https://github.com/foyez/go/tree/main/codes/concurrency)**
### Goroutines
- A **Goroutine** is a lightweight thread manged by the Go runtime
- Implemented by adding the `go` keyword before executing a function
- Tells go to spin up a new thread to do that thing
```go
```
## Web Servers
View contents
**[You can find all the code for this section here](https://github.com/foyez/go/tree/main/codes/webServers)**
```go
package main
import (
"fmt"
"log"
"net/http"
)
func home(w http.ResponseWriter, req *http.Request) {
fmt.Println("Home!")
fmt.Fprint(w, "Home!")
}
func main() {
http.HandleFunc("/", home)
fmt.Println("Server is running on port :8080")
log.Fatal(http.ListenAndServe(":8080", nil))
}
```
## Working with files
View contents
```go
import (
"fmt"
"os"
"strings"
)
type names string[]
func main() {
names := names{"Sohel", "Mithu", "Rupom"}
names.saveToFile("my_names")
fmt.Println(readNamesFromFiles("my_names"))
removeFile("my_names")
}
func (n names) toString() string {
return strings.Join(n, ",")
}
func (n names) saveToFile(filename string) error {
return os.WriteFile(filename, []bytes(n.toString()), 0666)
}
func readNamesFromFile(filename string) names {
bs, err := os.ReadFile(filename)
if err != nil {
fmt.Println("Error:", err)
os.Exit(1)
}
return strings.Split(string(bs), ",")
}
func removeFile(filename string) {
err := os.Remove(filename)
if err != nil {
fmt.Println("Error:", err)
}
}
```
## Generate random numbers
View contents
```go
import (
"math/rand"
"time"
)
source := rand.NewSource(time.Now().UnixNano())
r := rand.New(source)
// genrate random number from 0 to n
r.Intn(8) // n = 8
```
## Effective Go in short [ref](https://go.dev/doc/effective_go)
View contents
### Formatting with `gofmt`
View contents
Go uses `gofmt` to automatically format code, ensuring consistency across projects. Instead of manually aligning comments or indentation, developers rely on `gofmt`.
#### Key Formatting Rules:
1. **Indentation**: Uses **tabs**, not spaces.
2. **Line Length**: No strict limit; wrap long lines if needed.
3. **Parentheses**: Avoid unnecessary parentheses in control structures (`if`, `for`, `switch`).
#### Example:
**Before `gofmt`:**
```go
type T struct {
name string // name of the object
value int // its value
}
```
**After `gofmt`:**
```go
type T struct {
name string // name of the object
value int // its value
}
```
To format code, run:
```sh
gofmt -w filename.go
```
Or use:
```sh
go fmt ./...
```
This keeps your code clean and readable without manual effort.
### Commentary
View contents
Go supports both **C-style block comments (`/* */`)** and **C++-style line comments (`//`)**.
- **Line comments (`//`)** are the standard and widely used.
- **Block comments (`/* */`)** are mainly for package documentation or temporarily disabling code.
#### Example:
```go
package main
import "fmt"
// Greet prints a welcome message.
func Greet(name string) {
fmt.Println("Hello,", name)
}
/*
This is a block comment.
It is useful for package-level documentation or disabling large sections of code.
*/
func main() {
Greet("Foyez") // Calling the Greet function
}
```
**Doc comments** (before functions, structs, or packages) serve as the primary documentation.
For more details, check: [`go doc`](https://pkg.go.dev/cmd/doc).
### Names
View contents
Go follows clear and consistent naming conventions for better readability and usability.
#### 1️⃣ **Package Names**
- Use **short, lowercase, single-word** names.
- The package name should match its directory name.
✅ **Example:**
```go
import "bytes" // Use bytes.Buffer, not bytes_package.Buffer
```
```go
import "encoding/base64" // Imported as base64, not encodingBase64
```
#### 2️⃣ **Avoid Redundant Names**
- Names should be **concise and meaningful**.
- Use the **package name** as context.
✅ **Example:**
```go
buf := bufio.NewReader(input) // Not bufio.NewBufReader
r := ring.New() // Not ring.NewRing
```
#### 3️⃣ **Getters & Setters**
- Avoid `Get` in getter names.
- Use **exported (uppercase) methods** for getters, and `SetX` for setters.
✅ **Example:**
```go
type User struct {
owner string
}
func (u *User) Owner() string { return u.owner } // Not GetOwner()
func (u *User) SetOwner(o string) { u.owner = o } // Setter
```
```go
user := User{}
user.SetOwner("Foyez")
fmt.Println(user.Owner()) // Reads naturally
```
#### 4️⃣ **Interface Naming**
- **Single-method interfaces** should use `-er` suffix.
✅ **Example:**
```go
type Reader interface {
Read(p []byte) (n int, err error)
}
type Writer interface {
Write(p []byte) (n int, err error)
}
```
#### 5️⃣ **Use MixedCaps Instead of Underscores**
✅ **Example:**
```go
type DataProcessor struct {} // Not data_processor
func ProcessData() {} // Not process_data()
```
Following these conventions makes Go code **clean, idiomatic, and easy to read**.
### Semicolons
View contents
Go automatically inserts semicolons (`;`) where needed, so they are **mostly invisible** in source code. The rule:
👉 If a line ends with an **identifier, literal, or certain tokens (`return`, `break`, `}` etc.)**, Go **inserts a semicolon**.
#### ✅ **Examples:**
```go
x := 10 // Semicolon inserted automatically
fmt.Println(x) // Semicolon inserted automatically
```
#### **Semicolons in Loops**
Semicolons are required **only in `for` loops**:
```go
for i := 0; i < 5; i++ { // Semicolons required
fmt.Println(i)
}
```
#### **Incorrect Brace Placement**
🚨 **Wrong:**
```go
if x > 0 // Semicolon inserted → Unexpected behavior!
{
fmt.Println("Positive")
}
```
✅ **Correct:**
```go
if x > 0 { // No semicolon inserted
fmt.Println("Positive")
}
```
**Conclusion:** Let Go handle semicolons **automatically**, except in `for` loops or multiple statements on one line.
### Control Structures
View contents
Go's control structures are **similar to C** but with key differences:
✅ No `do` or `while`, just `for` loops
✅ `switch` is more flexible
✅ No parentheses `()` in conditions
✅ Braces `{}` are **mandatory**
---
#### **1. `if` Statement**
Braces `{}` are **always required**.
Optional **initialization** before condition.
✅ **Example:**
```go
if x := getValue(); x > 0 {
fmt.Println("Positive:", x)
}
```
✅ **No need for `else` if returning early:**
```go
f, err := os.Open("file.txt")
if err != nil {
return err
}
useFile(f)
```
---
#### **2. `for` Loop**
Go has **only `for`**, which works like `for`, `while`, and `forever` loops.
✅ **Standard `for` loop:**
```go
for i := 0; i < 5; i++ {
fmt.Println(i)
}
```
✅ **While-like loop:**
```go
for x > 0 {
x--
}
```
✅ **Infinite loop:**
```go
for {
fmt.Println("Running forever")
}
```
✅ **Loop over collections (array, slice, string, or map, or reading from a channel) using `range`:**
```go
for i, val := range arr {
fmt.Println(i, val)
}
for key, value := range oldMap {
newMap[key] = value
}
```
If you only need the first item in the range (the key or index), drop the second:
```go
for key := range myMap {
if key.expired() {
delete(myMap, key)
}
}
```
If you only need the second item in the range (the value), use the blank identifier, an underscore, to discard the first:
```go
for _, val := range arr { fmt.Println(val) }
```
✅ Go's `range` loop **automatically decodes UTF-8** and provides **rune values** (Unicode code points) instead of bytes.
**Example:**
```go
for pos, char := range "日本\x80語" { // \x80 is an invalid UTF-8 byte
fmt.Printf("character %#U starts at byte position %d\n", char, pos)
}
```
🛠 **Output:**
```
character U+65E5 '日' starts at byte position 0
character U+672C '本' starts at byte position 3
character U+FFFD '�' starts at byte position 6 // Invalid UTF-8 replaced
character U+8A9E '語' starts at byte position 7
```
- `range` **extracts Unicode runes**, not raw bytes.
- Invalid UTF-8 sequences are replaced with `U+FFFD (�)`.
- **Positions refer to bytes, not runes**.
✅ **Go Has No Comma Operator (`++` & `--` are Statements)** \
In Go:
- ✅ `++` and `--` are **statements, not expressions**
- 🚫 You **cannot** use them inside expressions like `x = y++ + z`
**Reverse an Array Using Parallel Assignment:**
```go
for i, j := 0, len(a)-1; i < j; i, j = i+1, j-1 {
a[i], a[j] = a[j], a[i] // Swap elements
}
```
---
#### **3. `switch` Statement**
✅ **No need for `break` (no fallthrough by default):**
```go
switch x {
case 1:
fmt.Println("One")
case 2, 3:
fmt.Println("Two or Three")
default:
fmt.Println("Other")
}
```
✅ **Can replace `if-else` chains:**
```go
x := 5
switch {
case x >= 1 && x <= 4:
fmt.Println("Between 1 to 4")
case x > 4:
fmt.Println("Greater than 4")
default:
fmt.Println("Zero")
}
```
✅ **Labeled `break` for loops:**
```go
Loop:
for i := 0; i < 5; i++ {
for j := 0; j < 5; j++ {
if i+j > 5 {
fmt.Println("Print only one time")
break Loop // Exits outer loop
}
}
}
```
---
#### **4. `type switch` (Detect Dynamic Type)**
```go
var i any = "hello"
switch v := i.(type) {
case int:
fmt.Println("Integer:", v)
case string:
fmt.Println("String:", v)
default:
fmt.Println("Unknown type")
}
```
---
### **Functions**
View contents
#### **1️⃣ Multiple Return Values**
Go allows functions to return multiple values, avoiding in-band error returns (like `-1` in C).
✅ **Example:** `Write` method in `os` package
```go
func (file *File) Write(b []byte) (n int, err error)
```
Returns:
- `n` → number of bytes written
- `err` → error (if not all bytes were written)
✅ **Example:** Extracting an integer from a byte slice
```go
func nextInt(b []byte, i int) (int, int) {
for ; i < len(b) && !isDigit(b[i]); i++ {}
x := 0
for ; i < len(b) && isDigit(b[i]); i++ {
x = x*10 + int(b[i]) - '0'
}
return x, i
}
```
Usage:
```go
for i := 0; i < len(b); {
x, i = nextInt(b, i)
fmt.Println(x)
}
```
---
#### **2️⃣ Named Return Parameters**
Return variables can be **named**, making code more readable.
✅ **Example:** Naming `value` and `nextPos`
```go
func nextInt(b []byte, pos int) (value, nextPos int) {
```
✅ **Example:** Simplifying `io.ReadFull`
```go
func ReadFull(r Reader, buf []byte) (n int, err error) {
for len(buf) > 0 && err == nil {
var nr int
nr, err = r.Read(buf)
n += nr
buf = buf[nr:]
}
return // Uses named return variables
}
```
---
#### **3️⃣ `defer` Statement (Delayed Execution)**
`defer` schedules a function to run **before the surrounding function exits**.
✅ **Example:** Ensuring a file closes
```go
func Contents(filename string) (string, error) {
f, err := os.Open(filename)
if err != nil {
return "", err
}
defer f.Close() // Ensures file closes before return
var result []byte
buf := make([]byte, 100)
for {
n, err := f.Read(buf)
result = append(result, buf[:n]...)
if err == io.EOF {
break
} else if err != nil {
return "", err
}
}
return string(result), nil
}
```
**Why use `defer`?**
✔ Guarantees cleanup (prevents leaks)
✔ Keeps code cleaner (close near open)
✅ **Example:** `defer` executes in LIFO order
```go
for i := 0; i < 5; i++ {
defer fmt.Print(i, " ")
}
// Output: 4 3 2 1 0
```
✅ **Example:** Function Tracing
```go
func trace(s string) string {
fmt.Println("entering:", s)
return s
}
func un(s string) {
fmt.Println("leaving:", s)
}
func a() {
defer un(trace("a"))
fmt.Println("in a")
}
func b() {
defer un(trace("b"))
fmt.Println("in b")
a()
}
func main() {
b()
}
```
**Output:**
```
entering: b
in b
entering: a
in a
leaving: a
leaving: b
```
**Why use `defer`?**
✔ Ensures cleanup, even if function exits early
✔ Improves readability and maintainability 🚀
### **Data**
View contents
**Memory Allocation: `new` vs. `make`**
View contents
Go provides two built-in functions for memory allocation:
- **`new(T)`** → Allocates zeroed storage for a value of type `T` and returns `*T` (a pointer).
- **`make(T, args)`** → Initializes slices, maps, and channels, returning `T` (not a pointer).
---
### **Allocation with `new`**
✅ **Usage:**
- Allocates memory but does not initialize beyond zero values.
- Returns a **pointer** to the allocated type.
✅ **Example:** Allocating a struct
```go
type SyncedBuffer struct {
lock sync.Mutex
buffer bytes.Buffer
}
p := new(SyncedBuffer) // Returns *SyncedBuffer
var v SyncedBuffer // Direct allocation, ready to use
```
✔ `p` is a pointer (`*SyncedBuffer`)
✔ `v` is a direct struct instance
✅ **Example:** Allocating an integer
```go
p := new(int) // *int with zero value (0)
fmt.Println(*p) // Prints 0
```
---
### **Constructors & Composite Literals**
✅ **When zero values aren’t enough, use a constructor.**
🔴 **Verbose version**
```go
func NewFile(fd int, name string) *File {
if fd < 0 {
return nil
}
f := new(File)
f.fd = fd
f.name = name
return f
}
```
✔ Can be **simplified** with **composite literals**
🟢 **Optimized version**
```go
func NewFile(fd int, name string) *File {
if fd < 0 {
return nil
}
return &File{fd, name, nil, 0} // Allocates and initializes
}
```
The fields of a composite literal are laid out in order and must all be present. However, by labeling the elements explicitly as field:value pairs, the initializers can appear in any order, with the missing ones left as their respective zero values. Thus we could say
```go
return &File{fd: fd, name: name}
```
✔ `&File{}` creates and returns an initialized struct
✔ Equivalent to `new(File)` but with initialization
✅ **Examples of composite literals:**
```go
a := [...]string{0: "no error", 1: "Eio", 2: "invalid argument"} // Array
s := []string{"no error", "Eio", "invalid argument"} // Slice
m := map[int]string{0: "no error", 1: "Eio", 2: "invalid argument"} // Map
```
---
### **Allocation with `make`**
✅ **`make` initializes slices, maps, and channels**
```go
v := make([]int, 10, 100) // Length 10, capacity 100
```
✔ Allocates an array of 100 integers
✔ Creates a slice of length 10 referring to that array
✅ **Key difference:**
```go
var p *[]int = new([]int) // *p == nil (rarely useful)
var v []int = make([]int, 100) // Allocates a slice of 100 ints
```
✔ `new([]int)` → Returns a pointer to an **empty** slice
✔ `make([]int, 100)` → Returns a **usable** slice of 100 ints
✅ **Idiomatic way:**
```go
v := make([]int, 100) // Best practice
```
✔ Avoid unnecessary complexity
✅ **Other `make` examples:**
```go
ch := make(chan int, 10) // Buffered channel
m := make(map[string]int) // Empty map
```
✔ `make` initializes internal structures
### **Arrys**
View contents
Arrays in Go differ from C-style arrays:
✔ **Arrays are values** → Assigning an array copies all elements.
✔ **Passing to a function copies the array** (unless using a pointer).
✔ **Array size is part of its type** → `[10]int` and `[20]int` are different types.
---
#### **1️⃣ Array Declaration & Initialization**
```go
var a [3]int // Zero-initialized: [0, 0, 0]
b := [3]int{1, 2, 3} // Explicit values
c := [...]int{4, 5, 6} // Compiler determines size
```
---
#### **2️⃣ Copying Arrays**
```go
a := [3]int{1, 2, 3}
b := a // Creates a copy, modifying b won’t affect a
b[0] = 10
fmt.Println(a, b) // Output: [1 2 3] [10 2 3]
```
---
#### **3️⃣ Passing Arrays to Functions**
🔴 **By Value (copying entire array)**
```go
func ModifyArray(arr [3]int) {
arr[0] = 100
}
a := [3]int{1, 2, 3}
ModifyArray(a)
fmt.Println(a) // Output: [1 2 3] (unchanged)
```
🟢 **By Reference (using pointers for efficiency)**
```go
func ModifyArray(arr *[3]int) {
arr[0] = 100
}
a := [3]int{1, 2, 3}
ModifyArray(&a)
fmt.Println(a) // Output: [100 2 3]
```
---
#### **4️⃣ Arrays vs. Slices**
✅ **Use slices for flexibility & efficiency**
```go
array := [3]float64{7.0, 8.5, 9.1}
slice := array[:] // Convert to slice
```
✔ Slices are more idiomatic in Go
---
### **Slices**
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Slices provide a **dynamic, flexible view** over arrays and are the preferred way to handle collections in Go.
✔ **Slices reference an underlying array** (modifications affect all references).
✔ **Passing a slice to a function allows modifications** without explicit pointers.
✔ **Slice length (`len`) and capacity (`cap`) can change dynamically.**
---
#### **1️⃣ Declaring & Initializing Slices**
```go
var s []int // nil slice (len=0, cap=0)
s = []int{1, 2, 3} // Initialized slice
t := make([]int, 5, 10) // Slice with len=5, cap=10
```
---
#### **2️⃣ Slicing an Array**
```go
arr := [5]int{1, 2, 3, 4, 5}
s := arr[1:4] // Slice of [2, 3, 4]
```
🔹 **Slices hold references to arrays, so modifying `s` affects `arr`**
```go
s[0] = 100
fmt.Println(arr) // Output: [1 100 3 4 5]
```
---
#### **3️⃣ Passing Slices to Functions**
```go
func modify(s []int) {
s[0] = 42
}
nums := []int{1, 2, 3}
modify(nums)
fmt.Println(nums) // Output: [42 2 3]
```
✔ No need to pass a pointer, as slices already reference the underlying array.
---
#### **4️⃣ Appending to Slices**
```go
s := []int{1, 2}
s = append(s, 3, 4, 5) // Expands the slice
fmt.Println(s) // Output: [1 2 3 4 5]
```
✔ If capacity is exceeded, Go automatically **allocates new memory**.
---
#### **5️⃣ Copying Slices**
```go
src := []int{1, 2, 3}
dst := make([]int, len(src))
copy(dst, src)
fmt.Println(dst) // Output: [1 2 3]
```
✔ `copy(dst, src)` copies **minimum of len(dst) and len(src)**.
---
#### **6️⃣ Two-Dimensional Slices**
🔹 **Independent inner slices:**
```go
matrix := make([][]int, 3) // 3 rows
for i := range matrix {
matrix[i] = make([]int, 4) // 4 columns
}
```
🔹 **Single allocation for efficiency:**
```go
matrix := make([][]int, 3)
data := make([]int, 3*4) // 3 rows * 4 cols
for i := range matrix {
matrix[i], data = data[:4], data[4:] // Slice the array into rows
}
```
✔ **More efficient** but less flexible than independent allocation.
---
### **Maps**
View contents
Maps in Go provide an efficient **key-value** data structure with dynamic sizing.
✔ **Keys must support equality (`==`)** (e.g., strings, ints, structs).
✔ **Maps hold references** to an underlying structure (modifying inside a function affects the caller).
✔ **Accessing a non-existent key returns the zero value** of the value type.
---
#### **1️⃣ Declaring & Initializing Maps**
```go
// Using map literals
timeZone := map[string]int{
"UTC": 0,
"EST": -5 * 3600,
"CST": -6 * 3600,
}
// Using make()
users := make(map[string]int) // Empty map
```
---
#### **2️⃣ Accessing & Modifying Maps**
```go
timeZone["PST"] = -8 * 3600 // Add key-value pair
offset := timeZone["EST"] // Retrieve value
fmt.Println(offset) // Output: -18000
```
❌ **Accessing a non-existent key returns the zero value** (for int, it's `0`).
---
#### **3️⃣ Checking Key Existence (Comma-Ok Idiom)**
```go
if offset, exists := timeZone["UTC"]; exists {
fmt.Println("Offset:", offset)
}
```
✔ Helps differentiate between **"zero value"** and **"missing key"**.
To test for presence in the map without worrying about the actual value, you can use the blank identifier (_) in place of the usual variable for the value.
```go
_, exists := timeZone[tz]
```
---
#### **4️⃣ Deleting Keys**
```go
delete(timeZone, "PST") // Remove PST from map
```
✔ Safe to call **even if the key doesn’t exist**.
---
#### **5️⃣ Using Maps as Sets**
```go
attended := map[string]bool{"Ann": true, "Joe": true}
if attended["Ann"] {
fmt.Println("Ann was at the meeting")
}
```
✔ **Maps with `bool` values** can function as sets.
---
#### **6️⃣ Iterating Over a Map**
```go
for key, value := range timeZone {
fmt.Println("Key:", key, "Value:", value)
}
```
---
### **Printing**
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Go’s `fmt` package provides **formatted printing** similar to C’s `printf`, but with enhanced features.
✔ `fmt.Print`, `fmt.Println`, `fmt.Printf` – Basic printing.
✔ `fmt.Sprintf`, `fmt.Fprintf` – Return formatted strings.
✔ `fmt.Fprint(os.Stdout, …)` – Print to `io.Writer`.
---
#### **1️⃣ Basic Printing**
```go
fmt.Print("Hello") // Prints: Hello
fmt.Println("Hello") // Prints: Hello\n (adds newline)
fmt.Printf("Age: %d\n", 25) // Prints: Age: 25
```
✔ `Println` adds spaces & newline.
✔ `Printf` supports format specifiers (`%d`, `%s`, etc.).
---
#### **2️⃣ Formatting Values (`Printf`)**
```go
x := 255
fmt.Printf("%d %x %b\n", x, x, x) // Decimal, Hex, Binary
// Output: 255 ff 11111111
t := struct{ Name string; Age int }{"John", 30}
fmt.Printf("%v\n", t) // {John 30} (default format)
fmt.Printf("%+v\n", t) // {Name:John Age:30} (field names)
fmt.Printf("%#v\n", t) // struct { Name string; Age int }{Name:"John", Age:30} (Go syntax)
```
✔ `%v` → default value representation.
✔ `%+v` → shows struct field names.
✔ `%#v` → prints Go syntax representation.
---
#### **3️⃣ Printing Maps & Slices**
```go
timeZone := map[string]int{"UTC": 0, "PST": -8 * 3600}
fmt.Printf("%v\n", timeZone) // map[PST:-28800 UTC:0]
fmt.Printf("%#v\n", timeZone) // map[string]int{"PST":-28800, "UTC":0}
```
✔ **Maps are sorted lexicographically by key**.
---
#### **4️⃣ Printing Types & Quotes**
```go
str := "Hello"
fmt.Printf("%T\n", str) // string (prints type)
fmt.Printf("%q\n", str) // "Hello" (quoted string)
fmt.Printf("%x\n", str) // 48656c6c6f (hex encoding)
fmt.Printf("% x\n", str) // 48 65 6c 6c 6f (spaced hex)
```
✔ `%T` → prints type.
✔ `%q` → quoted string.
✔ `%x` → hexadecimal representation.
---
#### **5️⃣ Custom String Representation (`String()` Method)**
```go
type Person struct {
Name string
Age int
}
func (p Person) String() string {
return fmt.Sprintf("%s is %d years old", p.Name, p.Age)
}
p := Person{"Alice", 25}
fmt.Println(p) // Alice is 25 years old
```
✔ Implement `String()` for **custom print formatting**.
---
#### **6️⃣ Variadic Functions (`...interface{}` & `...int`)**
```go
func Min(values ...int) int {
min := values[0]
for _, v := range values {
if v < min {
min = v
}
}
return min
}
fmt.Println(Min(3, 1, 4, 1, 5)) // 1
```
✔ `...int` → allows multiple `int` arguments.
---
### **Append**
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Go’s built-in `append` function dynamically grows slices.
#### **1️⃣ Syntax**
```go
func append(slice []T, elements ...T) []T
```
- `T` is a generic type.
- `append` returns a **new slice** because the underlying array **may change**.
---
#### **2️⃣ Appending Elements**
```go
x := []int{1, 2, 3}
x = append(x, 4, 5, 6)
fmt.Println(x) // [1 2 3 4 5 6]
```
✔ Adds multiple elements at once.
---
#### **3️⃣ Appending a Slice (`...` Operator)**
```go
x := []int{1, 2, 3}
y := []int{4, 5, 6}
x = append(x, y...) // Spreads `y` into `x`
fmt.Println(x) // [1 2 3 4 5 6]
```
✔ **`...` is required** to unpack a slice.
---
#### **4️⃣ Capacity Expansion & Performance**
```go
x := make([]int, 3, 5) // len=3, cap=5
x[0], x[1], x[2] = 1, 2, 3
x = append(x, 4, 5, 6) // Capacity exceeded → new array allocated
fmt.Println(x) // [1 2 3 4 5 6]
```
✔ If **capacity is exceeded, a new array is created**.
---
#### **5️⃣ Efficient Slice Growth (Doubling Strategy)**
```go
var s []int
for i := 0; i < 10; i++ {
s = append(s, i)
fmt.Printf("len=%d cap=%d %v\n", len(s), cap(s), s)
}
```
✔ **Capacity doubles dynamically** when needed.
---
## Learning Resources
View contents
- [Build web application with golang](https://github.com/astaxie/build-web-application-with-golang) - `A golang ebook intro how to build a web with golang`
- [Go Patterns](https://github.com/tmrts/go-patterns) - `Curated list of Go design patterns, recipes and idioms`
- [Learn Go with Tests](https://github.com/quii/learn-go-with-tests) - `Learn Go with test-driven development`
- [Go for Javascript Developers](https://www.pazams.com/Go-for-Javascript-Developers/)
- [Creating a RESTful API With Golang](https://tutorialedge.net/golang/creating-restful-api-with-golang/)
- [Go Tour](https://tour.golang.org/list)
- [Effective Go](https://golang.org/doc/effective_go.html)
- [Go by Example](https://gobyexample.com/)
- [GOSAMPLES](https://gosamples.dev/)
- [Go Doc](https://golang.org/doc/)
- [Go Blog](https://blog.golang.org/)
- [Clean Go Article](https://github.com/Pungyeon/clean-go-article)
- [How To Code in Go](https://www.digitalocean.com/community/tutorial_series/how-to-code-in-go)
### Video Tutorials
- [Go Tutorals - NerdCademy](https://youtube.com/playlist?list=PLujhHB_uAFJws6Vv5q1KDoaQ4YcpS9UOm)
- [Golang Tutorial for Beginners](https://www.youtube.com/watch?v=yyUHQIec83I) - `TechWorld with Nana`
- [Learn Go Programming - Golang Tutorial for Beginners](https://www.youtube.com/watch?v=YS4e4q9oBaU)
- [Learn Go Programming by Building 11 Projects – Full Course](https://www.youtube.com/watch?v=jFfo23yIWac)
- [Backend Master Class [Go + Postgres Docker + Kubernetes + gRPC]](https://youtube.com/playlist?list=PLy_6D98if3ULEtXtNSY_2qN21VCKgoQAE)