Package Scope

In Go, a package can span multiple files. All code within the same package can access each other's functions, variables, and types - even when they're defined in different files. This is called "package scope."

Understanding Package Scope

Every Go file starts with a package declaration:

package main

When multiple files have the same package declaration, they're all part of the same package and share everything with each other.

Multiple Files, One Package

Imagine you have a project with these files:

main.go:

package main

import "fmt"

func main() {
    fmt.Println(characterName)  // Using variable from fighter.go
    displayStats()              // Using function from fighter.go
}

fighter.go:

package main

import "fmt"

var characterName = "Goku"

func displayStats() {
    fmt.Println("Power Level: 9000")
}

Even though characterName and displayStats() are defined in fighter.go, they're accessible in main.go because both files belong to package main.

How It Works

When you run the program with go run ., Go compiles all .go files in the directory together as one package. This means:

• Variables defined in one file are accessible in all other files
• Functions defined in one file can be called from all other files
• Types defined in one file can be used in all other files
• Order of files doesn't matter

Example: Splitting Code Across Files

main.go:

package main

import "fmt"

func main() {
    goku := createFighter("Goku", 9000)
    vegeta := createFighter("Vegeta", 8500)
    
    winner := fight(goku, vegeta)
    fmt.Println(winner, "wins!")
}

fighter.go:

package main

type Fighter struct {
    Name       string
    PowerLevel int
}

func createFighter(name string, power int) Fighter {
    return Fighter{Name: name, PowerLevel: power}
}

battle.go:

package main

func fight(f1 Fighter, f2 Fighter) string {
    if f1.PowerLevel > f2.PowerLevel {
        return f1.Name
    }
    return f2.Name
}

All three files work together as one package! The main.go file can use createFighter() from fighter.go and fight() from battle.go.

Why Split Code Across Files?

Splitting code across multiple files helps with:

1. Organization - Group related functions together
2. Readability - Smaller files are easier to understand
3. Collaboration - Multiple people can work on different files
4. Maintenance - Easier to find and fix code

No Import Needed

Notice that you don't need to import anything to use code from other files in the same package:

// fighter.go
package main

var maxPower = 10000

// main.go  
package main

import "fmt"

func main() {
    fmt.Println(maxPower)  // No import needed!
}

As long as both files are in package main, they share everything automatically.

Assignment

For this challenge, you'll create a new file called player.go that defines variables which will be used by main.go.

main.go (already provided):

package main

import "fmt"

func main() {
    fmt.Println("Player:", playerName)
    fmt.Println("Level:", playerLevel)
    fmt.Println("Health:", playerHealth)
}

player.go (your task):

Inside the player.go file, create three package level variables

1. Create a package-level variable playerName with the value "Goku"
2. Create a package-level variable playerLevel with the value 9001
3. Create a package-level variable playerHealth with the value 100