Go Packages

Code is organized by packages in Go. They are similar to Python's modules and JavaScript's npm modules.

What is main

The most common package in Go is main because main package is served as an entry point to any Go program.

For example:

package main

import "fmt"

func HelloWorld() {
  fmt.Println("Hello World!")
}

HelloWorld()

This will not compile and throw an error. You must call your functions inside the main function.

package main

import "fmt"

func HelloWorld() {
  fmt.Println("Hello World!")
}

func main() {
  HelloWorld()
}

Non-main Packages

We can write our own packages. However, we cannot run a non-main package directly. We must import it into the main package. For example, create a new folder in helloworld and call it foo. Inside the folder, make a file called foo.go.

package foo

func SayHello() {
  fmt.Println("Foo says hello")
}

Now we can import the package into the main program and run foo.SayHello.

// => hello_world/main.go
package main

import (
  "fmt"
  "go-academy/helloworld/foo"
)

func main() {
  fmt.Println("Hello World, this is Go!")
  SayHello()
  SayBye()
  foo.SayHello()
}