Refactoring: Refactorings/Change Reference to Value

A reference object can become small, immutable, and awkward to manage.

Mechanics

1. Check that the candidate object is immutable or can become immutable (Try using Remove Setting Method). If not, abandon this refactoring.
2. Create an == method and an eql? method (eql? can delegate to ==)
3. Create a hash method
4. Test
5. Consider removing factory method and making a public constructor.

Example

Before

class Currency
  attr_reader :code

  def initialize(code)
    @code = code
  end

  def self.get(code)
    # return currency from registry
  end
end

# usage
usd = Currency.get("USD")

Currency.new("USD") == Currency.new("USD") # returns false

After

class Currency
  attr_reader :code

  def initialize(code)
    @code = code
  end

  def self.get(code)
    # return currency from registry
  end

  def eql?(other)
    self == (other)
  end

  def ==(other)
    other.equal?(self) || (other.instance_of?(self.class) && other.code == code)
  end

  def hash
    code.hash
  end
end

# usage
Currency.send(:new, "USD") == Currency.new("USD") # returns true