How does Go implement encapsulation without private/public class modifiers?

Go's encapsulation is package-level, not class-level. Identifiers (types, fields, functions, methods) are exported (public) if they start with an uppercase letter, and unexported (package-private) if they start with a lowercase letter. There is no private, protected, or public keyword.

// package accounts

// Exported type — usable outside the package
type Account struct {
    owner   string  // unexported — only accessible within package accounts
    balance float64 // unexported
    ID      int     // exported field
}

// Constructor (factory function) — controls how Account is created
func NewAccount(owner string, initialBalance float64) (*Account, error) {
    if initialBalance < 0 {
        return nil, fmt.Errorf("initial balance cannot be negative")
    }
    return &Account{owner: owner, balance: initialBalance}, nil
}

// Exported getter
func (a *Account) Balance() float64 { return a.balance }
func (a *Account) Owner()   string  { return a.owner }

// Exported mutator with validation
func (a *Account) Deposit(amount float64) error {
    if amount <= 0 {
        return fmt.Errorf("deposit amount must be positive")
    }
    a.balance += amount
    return nil
}

// In main package:
acc, _ := accounts.NewAccount("Alice", 100.0)
fmt.Println(acc.Balance())    // 100.0 — OK
// acc.balance = 9999          // COMPILE ERROR: acc.balance is unexported
// acc.owner = "Hacker"       // COMPILE ERROR
acc.Deposit(50.0)              // OK — goes through validation

Differences from Java/C++: Go has no protected — there is no concept of subclass access. Unexported fields are invisible even to embedding structs in other packages. The internal package mechanism provides a stronger form of encapsulation: code in foo/internal/bar can only be imported by code rooted at foo.

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