Exported and Unexported Identifiers

Go uses the first letter of an identifier to control access from other packages instead of separate public or private keywords.

An identifier beginning with an uppercase Unicode letter is exported from its package. Lowercase identifiers are accessible inside the same package but cannot be referenced directly by an importer. These rules apply to functions, types, variables, constants, methods and struct fields.

Names still matter inside a package: an exported struct type may contain an unexported field. Design exported APIs intentionally because their names become contracts callers rely on.

Follow this diagram before executing the example. Check where a value or decision changes what runs next.

This example is a complete program. Save it as main.go or paste it into the Go Playground.

Go code

package main

import "fmt"

type Account struct {
	Owner string
	pin   int
}

func (a Account) Masked() string { return a.Owner + ": ****" }
func main() {
	a := Account{Owner: "Maya", pin: 1234}
	fmt.Println(a.Masked())
}

Output

Maya: ****

Inside the defining package, both Owner and pin can be initialized. Masked returns an exported method; an importing package can use Owner and Masked but cannot directly access the lowercase pin field.

• An uppercase field of an exported type is exposed as part of its package API.
• Exported does not mean globally mutable or automatically safe to use concurrently.

Create an exported function Describe that reads a private field and returns a user-friendly description.

Tip: Edit the example above, predict the output, and run the modified code to test your reasoning.

You have practiced Exported and Unexported Identifiers in a small, self-contained program. The important habit is to predict what runs, inspect the actual output and distinguish the language rule from the particular example.

Before continuing, make sure you can explain the program to someone who has not seen it, including the line that changes its result.