我有这段代码:
- date_counter = Time.mktime(2011,01,00,"+05:00")
- @weeks = Array.new
- (date_counter..Time.now).step(1.week) do |week|
- logger.debug "WEEK: " + week.inspect
- @weeks << week
- end
- Sat Jan 01 00:00:00 -0500 2011
- Sat Jan 08 00:00:00 -0500 2011
- Sat Jan 15 00:00:00 -0500 2011
- etc.
但执行时间完全是垃圾!每周计算大约需要4秒钟.
我在这段代码中遗漏了一些奇怪的低效率吗?看起来很简单.
我正在使用Rails 3.0.3运行Ruby 1.8.7.
解决方法
假设MRI和Rubinius使用类似的方法生成范围,所有无关检查使用的基本算法和一些Fixnum优化等被删除是:
- class Range
- def each(&block)
- current = @first
- while current < @last
- yield current
- current = current.succ
- end
- end
- def step(step_size,&block)
- counter = 0
- each do |o|
- yield o if counter % step_size = 0
- counter += 1
- end
- end
- end
对于Time对象,#succ会在一秒后返回时间.因此,即使你每周都要求它,但无论如何它必须在两次之间逐步完成.
编辑:解决方案
构建一系列Fixnum,因为它们具有优化的Range#step实现.
就像是:
- date_counter = Time.mktime(2011,"+05:00")
- @weeks = Array.new
- (date_counter.to_i..Time.now.to_i).step(1.week).map do |time|
- Time.at(time)
- end.each do |week|
- logger.debug "WEEK: " + week.inspect
- @weeks << week
- end