class HasToStr
  def to_str
    raise
  end

  def ==(other)
    puts "HasToStr: comparing to #{other}"
    true
  end
end

class DoesNotHaveToStr
  def ==(other)
    puts "DoesNotHaveToStr: comparing to #{other}"
    true
  end
end

puts "hello" == HasToStr.new
# => HasToStr: comparing to hello
# => true
puts "hello" == DoesNotHaveToStr.new
# => false