Question

我希望能够将Ruby中的Enumerable对象扩展为一个无限的星期一列表（例如）。

所以它会产生：3月29日，4月5日，4月12日......等等。

我如何在Ruby中实现它？

Answer 1

在1.9（以及可能使用backports的早期版本）中，您可以轻松创建枚举器：

require 'date'

def ndays_from(from, step=7)
  Enumerator.new {|y|
    loop {
      y.yield from
      from += step
    }
  }
end

e = ndays_from(Date.today)
p e.take(5)
#=> [#<Date: 2010-03-25 (4910561/2,0,2299161)>, #<Date: 2010-04-01 (4910575/2,0,2299161)>, #<Date: 2010-04-08 (4910589/2,0,2299161)>, #<Date: 2010-04-15 (4910603/2,0,2299161)>, #<Date: 2010-04-22 (4910617/2,0,2299161)>]

Answer 2

将Date存储为实例变量，初始化为星期一。您将实施each方法，使用date += 7将存储日期增加7天。

Answer 3

您可以通过延长日期来做某事......


#!/usr/bin/ruby

require 'date'

class Date
  def current_monday
    self - self.wday + 1
  end

  def next_monday
    self.current_monday + 7
  end
end

todays_date = Date.today
current_monday = todays_date.current_monday
3.times do |i|
  puts current_monday.to_s
  current_monday = current_monday.next_monday
end

2010-03-22
2010-03-29
2010-04-05
2010-04-12

...当然有关于扩展基类的常见警告。

Answer 4

您可以使用nw方法 mondays

扩展Date类

class Date
  def self.mondays(start_date=Date.today, count=10)
    monday = start_date.wday > 1 ? start_date - start_date.wday + 8 : start_date - start_date.wday + 1
    mondays = []
    count.times { |i| mondays << monday + i*7}
    mondays
  end
end

Date.mondays将默认返回星期一数组，其中包含从最接近的星期一到Date.today的10个元素。您可以传递参数：

Date.mondays(start_date:Date, count:Integer)

start_date - 开始点找到最接近的星期一 count - 你正在寻找的星期一的数量

IE：

Date.mondays(Date.parse('11.3.2002'))
Date.mondays(Date.parse('11.3.2002'), 30)

Answer 5

module LazyEnumerable
  extend Enumerable

  def select(&block)
    lazily_enumerate { |enum, value| enum.yield(value) if 
block.call(value) }
  end

  def map(&block)
    lazily_enumerate {|enum, value| enum.yield(block.call(value))}
  end

  def collect(&block)
    map(&block)
  end

  private

  def lazily_enumerate(&block)
    Enumerator.new do |enum|
      self.each do |value|
        block.call(enum, value)
      end
    end
  end
end

...........

class LazyInfiniteDays
  include LazyEnumerable

  attr_reader :day

  def self.day_of_week
    dow = { :sundays => 0, :mondays => 1, :tuesdays => 2, :wednesdays => 
3, :thursdays => 4, :fridays => 5, :saturdays => 6, :sundays => 7 }
    dow.default = -10
    dow
  end

  DAY_OF_WEEK = day_of_week()

  def advance_to_midnight_of_next_specified_day(day_sym)
    year = DateTime.now.year
    month = DateTime.now.month
    day_of_month = DateTime.now.day
    output_day = DateTime.civil(year, month, day_of_month)
    output_day += 1 until output_day.wday == DAY_OF_WEEK[day_sym]
    output_day
  end

  def initialize(day_sym)
    @day = advance_to_midnight_of_next_specified_day(day_sym)
  end

  def each
    day = @day.dup
    loop {
      yield day
      day += 7
    }
  end

  def ==(other)
    return false unless other.kind_of? LazyInfiniteDays
    @day.wday == other.day.wday
  end
end

如何创造无数可数的时代？

5 个答案: