Golang/Basics

Main function

package main
import (
	"fmt"
	"time"
)

func main()         {
	fmt.Println("Welcome", time.Now())
}

Struct

package main
import "fmt"
type Student struct { // structure or user define data. Object.
	rollno int        // properties
	name string
	marks int
}

func main() {
	var student1 Student = Student{101,"Piotr",55} // variable is the Student type. It's an object.
	fmt.Println(student1)
	fmt.Println(student1.name)
 
	var student2 Student = Student{rollno: 102, marks: 98}
	fmt.Println(student2)
	fmt.Println(student2.name) // this prints empty line as the 'name' property of the variable 'student2' has not been assigned any value
}

go run struct.go 
{101 Piotr 55}
Piotr
{102  98}

Go modules and custom packages

A Go Module is a collection of Go packages.

A module is a collection of packages that are released, versioned, and distributed together. Modules may be downloaded directly from version control repositories or from module proxy servers.

Why do we need Go modules to create a custom package? The answer is the import path for the custom package we create is derived from the name of the go module. In addition to this, all the other third-party packages(such as source code from github) which our application uses will be present in the go.mod file along with the version. This go.mod file is created with go mod init <mymodule> when we create a new module.

# in directory mymodule/ initialize a module <mymodule>
go mod init mymodule

$ cat go.mod
module mymodule
go 1.17

The mymodule is the base path to import any package created inside this module.

Source files belonging to a package should be placed in separate folders of their own. It is a convention(requirment) in Go to name this folder with the same name as the package. Example structure:

mymodule -> # 'go mod init mymodule'
 |- main.go # -> package "main"
 |- tools
      |- helper.go # -> package "tools" as the folder name

To import tools package from main.go import this "mymodule/tools"

Siliencers

are useful to silience errors during development:

• import a package before using it error "imported and not used"
• import a package just to make sure the initialization takes place even though we do not need to use any function or variable from the package

Silienced by using it

package main
import (  
        "learnpackage/simpleinterest"
)
var _ = simpleinterest.Calculate
func main() {
}

Silienced import

import (  
    _ "learnpackage/simpleinterest"
)