减少coffeescript中的循环 [英] Decrementing for loop in coffeescript

问题描述

我知道如何对coffeescript中的循环进行递增，例如：

Coffeescript：

  for some in something 
  

生成的Javascript：

  for（_i = 0，_len = something.length; _i< _len; _i ++）
  pre> 
 
 
如何在Coffeescript中创建类似于此的递减for循环？
  for（var i = something.length-1; i> = 0; i--）
  
 
 
解决方案
 编辑：支持CoffeeScript 1.5  by -1 语法。 > 
 
 
首先，您应该熟悉关键字，可以指定一个步骤。其次，您必须了解，CoffeeScript编译器对循环端点采用非常朴素的方法（请参见问题1187  ，其中Blender链接到），这意味着
 对于某些东西通过-1＃不要这样做！ 
 
将导致无限循环 - 它从索引0开始，将索引递增-1，然后等待直到索引命中 something.length 。 Sigh。
 
 
 
因此，您需要使用范围循环语法，让您自己指定这些端点，但也意味着您必须自己抓取循环项： p> 
 
 
  for i in [something.length  -  1..0] by -1 
 some = something [i] 
  
显然这很乱。所以你应该强烈地考虑迭代 something.reverse（）。只要记住， reverse（）修改你调用它的数组！如果你想保留一个数组，但要反向迭代，你应该复制它：
 对于something.slice ）.reverse（）
  
 
I know how to do a incrementing for loop in coffeescript such as:

Coffeescript:
for some in something
Generated Javascript:
for (_i = 0, _len = something.length; _i < _len; _i++)
How do I create a decrementing for loop similar to this in Coffeescript?
for (var i = something.length-1; i >= 0; i--)

解决方案
EDIT: As of CoffeeScript 1.5 by -1 syntax is supported.

First, you should familiarize yourself with the by keyword, which lets you specify a step. Second, you have to understand that the CoffeeScript compiler takes a very naïve approach to loop endpoints (see issue 1187, which Blender linked to), which means that
for some in something by -1 # don't do this!!!
will result in an infinite loop—it starts at index 0, increments the index by -1, and then waits until the index hits something.length. Sigh.

So you need to use the range loop syntax instead, which lets you specify those endpoints yourself—but also means you have to grab the loop items yourself:
for i in [something.length - 1..0] by -1
  some = something[i]
Obviously that's pretty messy. So you should strongly consider iterating over something.reverse() instead. Just remember that reverse() modifies the array that you call it on! If you want to preserve an array but iterate over it backwards, you should copy it:
for some in something.slice(0).reverse()


                        
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