GO Basic Command Line

Table of Content:

Installation and Setup

Create go.mod file to your project

$ mkdir go-basic && cd go-basic
$ go mod init go-basic

Create go file and main package

package main

func main() {
    println("Hello World")
}

Import format

package main

import "fmt"

func main() {
    fmt.Printf("Hello %v\n", "World")
}

Warning: \ The GO is separate end of line with ; and fix the {} syntax.

Test run main package

go run main.go

Declare in GO

var is mutable and const is immutable

var x int  // declared but not used

var x int
_ = x

var x int = 10
print(x)

Short declaration

y := 10

Note: \ All variable in GO have default value, in GO it call zero value.

Note: \ When to use short declaration
package main

var x int

func main() {
    y := 10
}

If Statement

point := 50
if point >= 50 && point <= 100 {
    println("Pass")
} else if point >= 20 {
    println("Not Pass")
}

For Loop

values := []int{1, 2, 3, 4, 5}

for i := 0; i < len(values); i ++ {
    println(values[i])
}

values := []int{10, 20, 30, 40}

for i, v := range values {
    println(i, v)
}

Note: \ If you do not want to use index in for-each statement, you can use
for _, v := range values {
    println(V)
}

While Loop

values := []int{1, 2, 3, 4, 5}

i := 0
for i < len(values) {
    println(values[i])
    i++
}

Array

// array of int with size 3
var x [3]int = [3]int{1, 2, 3}

x := [3]int{1, 2, 3}

x := [...]int{1, 2, 3, 4}

// Create slice array
x := []int{1, 2, 3}
x = append(x, 4)

Map

var countries map[string]string

countries := map[string]string{}
countries["th"] = "Thailane"

country, ok := countries["jp"]
if !ok {
    println("No value")
    return
}

Function

The scope of function is in package

func main() {
    c, _ := add(10, 20)
    println(c)
}

func add(a, b int) (int, string) {
    return a + b, "Hello"
}

x := func(a, b int) int {
    return a + b
}
value := x(10, 20)
println(value)

func sum(a ...int) int {
    s := 0
    for _, v := range a {
        s += v
    }
    return s
}

s := sum(1, 2, 3, 4, 5)
println(s)

High-order Function

func cal(f func(int,int)int) {
    sumn := f(50, 10)
    println(sum)
}

cal(func(a, b int) int {
    return a + b
})

Package

project
    |-- customer
    |   |- customer.go
    |- go.mod
    |- main.go

// customer.go
package customer

var Name = "Customer"

// main.go
import "project/customer"

func main() {
    println(customer.Name)
}

Warning: \ In GO, if you want to export anything from another package, you should use pascal case like, func Sum() or var Name =

Pointer

var x, y int
x = 10
y = x

// return pointer in memory
println(&x)
println(&y)

0xc0000140e0
0xc0000ae010

var x int
x = 10

var y *int
y = &x

// return pointer in memory
println(&x)
println(y)

0xc000122008
0xc000122008

Note: \ If you want to use value of pointer y, you can use println(*y).

Struct

Struct is a class without method in GO. Attribute in GO say with behavior.

type Person struct {
    Name string
    Age int
}

func main() {
    x := Person{"Tom", 18}
    y := Person{Name: "Tom", Age: 18}
    z := Person{
        Name: "Tom",
        Age: 18,
    }

    println(x.Name)
    println(y.Age)
}

Create Extension Method

func Hello(p Person) string {
    return "Hello " + p.Name
}

println(Hello(x))

func (p Person) Hello() string {
    return "Hello " + p.Name
}

println(Hello(x))
println(x.Hello())

Create OOP in Struct

package customer

type Person struct {
    name string
    age int
}

func (p Person) GetName() string {
    return p.name
}

func (p *Person) SetName() string {
    p.name = name
}

func (p Person) GetAge() int {
    return p.age
}

x := customer.Person{}
x.SetName("Tom")
println(x.GetName())

Tom

References

https://www.youtube.com/watch?v=JbIS97exQnQ
https://github.com/avelino/awesome-go