Partially immutability in object construction in Ruby.

immutable_ruby1.rb

class Profile
  def initialize(email)
    self.class.send :define_method, :email, -> { email }
  end
end

p = Profile.new 'foo@bar.com'
p.email #=> 'foo@bar.com'
p.email = 'hey@now.com' #=> <boom>
p.instance_variable_set :@email, 'hey@now.com'
p.email #=> 'foo@bar.com'