ruby - 如何从特定数字制作序列？

Question

如何从平方数的开头制作序列，然后将其添加到上一个结果中？

7 => 49, 56, 63, ...

def make_sequence(number)
  lambda { number*number ??? }
end

num = make_sequence(7)
num.call #=> 49
num.call #=> 56
...

Answer 1

按照你最初的想法使用闭包我会写：

def make_sequence(n)
  x = n**2 - n
  lambda { x += n }
end

num = make_sequence(7)
p num.call #=> 49
p num.call #=> 56

Answer 2

使用枚举器

def make_sequence(start)
  pos = start**2
  Enumerator.new do |y|
    loop do
      y.yield(pos)
      pos += start
    end
  end
end

seq = make_sequence(7)
seq.next   #=> 49
seq.next   #=> 56

...

Answer 3

光纤版本：

def make_sequence(num)
  inc = num
  num = num*num
  Fiber.new do
    loop do
      Fiber.yield(num)
      num += inc
    end
  end
end

a = make_sequence(7)
p a.resume  #=> 49
p a.resume  #=> 56
p a.resume  #=> 63
...