Package

In Go, a package is a collection of related Go source code files that can be compiled together and used as a unit. Packages are used to organize Go code into reusable and maintainable units. Each package has a unique name that is used to identify it and to refer to its contents from other packages.

Everything in Go lives in a package, every Go source file starts with a package declaration.

package main

import "fmt"

func main() {
	fmt.Println("Hello, world!")
}

Everything in Go source code is either a package scope or function scope

Package level declaration:

If we declare anything out of our function before the main() function in the source file it is inside a package scope. We cannot use a short deceleration operator while declaring package scope := and the declaration should always start with a keyword, making it easier to parse.

const AdminID = 69
var newID string

type user struct{
	...
}

if we think about it alll the function inside a source file is at package scope too.

Package visibility:

Go uses encapsulation(information hiding) when it comes to packages. whenever we write a package we don’t want to allow everyone to use everything, some things are kept private in the package. So how do we define things that can be exported? It’s easy, Everyname that starts with a capital letter can be exported and used by another package

//this cannot be exporetd
type internal struct {
	...
}

//this is exportable
func AllData() {
}

a package usually does not contain a single source file but multiple source files which contains exportable variables and functions.

fmt.Println()

fmt package contains Println function which can be used by other package there are some things that start with lowercase letter inside fmt packgae that are private to the fmt