Public Mutable Field (ARCH6186)

Key ruby.quality.public-mutable-attr · Severity warning · Category quality

Directly exposed mutable fields (attr_accessor) bypass validation and invariants; the object’s internal state can be corrupted from anywhere.

Incorrect

class Account
  attr_accessor :balance

  def initialize
    @balance = 0
  end
end

Correct

class Account
  attr_reader :balance

  def initialize
    @balance = 0
  end

  def deposit(amount)
    raise ArgumentError if amount.negative?
    @balance += amount
  end
end

Fix

Drop the writer and route state changes through explicit methods that enforce validation.