Public Mutable Field (ARCH5186)

Key go.quality.exported-mutable-field · Severity info · Category quality

Directly exported mutable fields make it impossible to enforce invariants and leak internal state. Hide the field and expose accessors.

Incorrect

type Account struct {
    Balance int // anyone can write freely
}

Correct

type Account struct {
    balance int
}

func (a *Account) Balance() int { return a.balance }

func (a *Account) Deposit(n int) error {
    if n <= 0 {
        return errInvalidAmount
    }
    a.balance += n
    return nil
}

Fix

Make the field unexported and add accessor methods that enforce invariants.