Ruby - Métodos de instância VS de classe VS lambda

01_metodos_de_instancia.rb

class Calc
  def sum(a, b)
    a + b
  end

  def multiply(a, b)
    a * b
  end
end

calc = Calc.new

puts calc.sum(3, 3) # 6

puts calc.multiply(3, 3) # 9

02_metodos_de_classe.rb

class Calc
  def self.sum(a, b)
    a + b
  end

  def self.multiply(a, b)
    a * b
  end
end

puts Calc.sum(3, 3) # 6

puts Calc.multiply(3, 3) # 9

03_modulos_como_classes_q_fazem_uma_coisa.rb

module Calc
  class Sum
    def self.call(a, b)
      a + b
    end
  end

  class Multiply
    def self.call(a, b)
      a * b
    end
  end
end

puts Calc::Sum.call(3, 3) # 6

puts Calc::Multiply.call(3, 3) # 9

04_modulos_com_lambdas.rb

module Calc
  Sum = -> (a, b) { a + b }

  Multiply = -> (a, b) { a * b }
end

puts Calc::Sum.call(3, 3) # 6

puts Calc::Multiply.call(3, 3) # 9