Getting started

Anatomy of a Go program

Let's revisit the previous program line by line.

package main
 
import "fmt"
 
func main() {
	fmt.Println("Hello, Go!")
}

`package main` declares the package this file belongs to. The `main` package is special: it's the one that produces an executable (any other package name produces a library). `import "fmt"` imports the standard formatted I/O package, which provides `Println`, `Printf`, `Sprintf`, and so on. `func main()` is the entry point: in a `main` package, this function is called automatically on startup.

Go refuses to compile a file that imports an unused package, or declares a local variable that is never read. This isn't a warning: it's a compile error. This strictness prevents dead code from piling up.

A real Go project is organized around a module, declared in a `go.mod` file at the root. It defines the module's import path and the Go version used, and references external dependencies.

go mod init example.com/hello

Creates a minimal go.mod file to start a module.

module example.com/hello
 
go 1.23

Generated content: the module path, then the required Go version.

Your turn

Without running any code: does the following file compile? Justify your answer. package main import ( "fmt" "os" ) func main() { fmt.Println("Hello") }

// Réfléchis avant de révéler la solution.

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