Install Go, write hello world, understand go run vs go build.

Packages, Imports, and Exported Names

Every Go file starts with a package declaration. A package is just a folder of .go files that share a name. When you import that package, you get everything in it that starts with a capital letter.

Packages

A directory of .go files = one package. By convention the folder name and the package name match.

project/
├── main.go            // package main
└── greet/
    └── greet.go       // package greet

Imports

Use the import keyword to bring in other packages — either standard library or third-party modules.

If you import a package you don't use, the program won't compile. Go enforces tidiness — unused imports rot quickly and slow builds down, so the language refuses to ship them.

Grouping & aliases

By convention, imports are split into groups (stdlib first, third-party next), separated by blank lines. goimports does this for you.

import (
    "fmt"
    "strings"

    "github.com/google/uuid"
)

You can rename an import inline — useful when two packages share the same name:

import (
    "encoding/json"

    yamljson "github.com/ghodss/yaml" // local alias
)

The blank identifier _ lets you import a package purely for its side effects (typically a func init() that registers a database driver, image format, etc.):

import _ "github.com/lib/pq" // registers the Postgres driver

Exported vs unexported names

Go has a one-rule visibility system:

• Names starting with a capital letter are exported — visible to other packages.
• Names starting with a lowercase letter are package-private.

package greet

func Hello(name string) string { // exported — anyone can call greet.Hello
    return "hi, " + clean(name)
}

func clean(s string) string { // unexported — only files in `greet` can call it
    return strings.TrimSpace(s)
}

This even applies to struct fields. In type User struct { Name string; age int }, other packages can read u.Name but cannot see u.age.

The standard library

Go ships with a famously thorough standard library. A few you'll use immediately:

| Package | What it does | | --------------- | ------------------------------------------- | | fmt | Formatted I/O (Println, Printf, Sprintf). | | strings | Manipulate UTF-8 strings. | | strconv | Convert strings ↔ numbers. | | os | OS calls, env vars, os.Args. | | io | Reader / Writer interfaces. | | net/http | HTTP client and server. | | encoding/json | JSON encode / decode. | | time | Times, durations, tickers. |