inject_sym.rb

class Foo
  def initialize(n)
    @n = n
  end

  attr_reader :n

  def abracadabra_alakazam(x)
    Foo.new(n + x.n)
  end
end

[Foo.new(1), Foo.new(2), Foo.new(3)].inject :abracadabra_alakazam