Go Basics

Hello World

package main

import "fmt"

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

Every Go program starts in package main. Execution begins in func main().

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Packages

Every Go program is made of packages. By convention, the package name matches the last element of the import path — math/rand contains files that begin with package rand.

import (
	"fmt"
	"math/rand"
)

func main() {
	fmt.Println("My favorite number is", rand.Intn(10))
}

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Imports

Use the factored import statement (preferred style):

import (
	"fmt"
	"math"
)

Single import is also valid: import "fmt"

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Exported Names

A name is exported if it begins with a capital letter.

• Pizza, Pi → exported ✅
• pizza, pi → unexported ❌

When importing a package you can only use its exported names.

fmt.Println(math.Pi)   // ✅
fmt.Println(math.pi)   // ❌ compile error: undefined

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Comments

// Single-line comment

/*
   Multi-line comment
*/

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Dependency Tracking

External packages are tracked via go.mod:

go mod init <module-path>   # creates go.mod

go.sum contains cryptographic hashes of all direct + indirect dependencies for integrity verification:

rsc.io/quote v1.5.2 h1:w5fcysjrx7yqtD/aO+QwRjYZOKnaM9Uh2b40tElTs3Y=
rsc.io/quote v1.5.2/go.mod h1:LzX7hefJvL54yjefDEDHNONDjII0t9xZLPXsUe+TKr0=

Each line: <module-path> <version> <hash> (hash = algo:base64)

go mod tidy   # add missing hashes, remove unused ones

External packages are found at pkg.go.dev.

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Compilation

Go is compiled. Two kinds of errors:

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String Formatting

Format Verbs

s := fmt.Sprintf("I am %d years old and %.2f meters tall", 25, 1.75)
// "I am 25 years old and 1.75 meters tall"