Packages and func main

Go has no public or private keywords, no header files, no elaborate module ceremony. It has packages and one delightful trick.

Packages: folders of shared purpose

Every Go file starts with a package declaration; files in one directory share one package. The standard library is a treasury of them:

The grouped import ( ... ) form pulls in several packages. You call into a package as packagename.Function.

The capitalization rule

Here's Go's famous trick — the first letter decides visibility:

• strings.ToUpper — Capitalized = exported (usable from other packages)
• strings.toLower (imagine) — lowercase = unexported (package-private)

No keywords. You can read any Go code and instantly know what's public API and what's internal: just look at the case. This is why it's fmt.Println, not fmt.println.

Where main fits

An executable needs exactly two things: package main and func main(). The := you spotted above declares-and-assigns in one stroke — Go infers the type. It's the workhorse of Go code, and next camp dives into it properly.