CoffeeScript for循环获取迭代器var [英] CoffeeScript for loop get iterator var

问题描述

在coffescript中，我有

In coffescript I have

arr = ["a","b","c"]
for i in [0..arr.length] by 1
  if (sometimesTrue)
    arr.pop()
    i--

但它被翻译成：

var arr, i, _i, _ref;

arr = ["a", "b", "c"];

for (i = _i = 0, _ref = arr.length; _i <= _ref; i = _i += 1) {
  if (sometimesTrue) {
    arr.pop();
    i--;
  }
}

你可以看到这个循环使用 _i 作为参考而不是 i ，所以我的 i - t真的做任何事情。

You can see that this loop uses a _i as the reference rather than i so my i-- doesn't really do anything.

由于在这个循环中，数组的长度改变，我需要找出如何处理这个...有什么办法做一个for循环？或者我需要切换到一段时间吗？

Since in this loop, the length of the array changes, I sort of need to figure out how to handle this... Is there any way to do this with a for loop? Or do I need to switch to a while?

推荐答案

CoffeeScript将计算循环边界一次，因此在你迭代它的时候改变数组只会产生一个混乱。

CoffeeScript will compute the loop bounds once and you can't reset the calculation so changing the array while you're iterating over it will just make a big mess.

例如：

f(i) for i in [0..a.length]

b $ b

变为：

becomes this:

var i, _i, _ref;
for (i = _i = 0, _ref = a.length; 0 <= _ref ? _i <= _ref : _i >= _ref; i = 0 <= _ref ? ++_i : --_i) {
  f(i);
}

请注意，当 _ref时，迭代次数是固定的是在循环开始时计算的。另请注意， i 将在每次迭代中分配一个新值，所以您对 i 被忽略。注意，循环 [0..a.length] 会执行 a.length + 1 迭代， code> a.length 迭代; [a..b] 产生一个封闭间隔（即包含两个端点）， [a ... b] 给你一个半开的间隔（即 b 不包括）。类似地，这：

Note that the number of iterations is fixed when _ref is computed at the beginning of the loop. Also note that i will be assigned a new value on each iteration so any changes you make to i inside the loop will be ignored. And, note that looping over [0..a.length] does a.length+1 iterations, not a.length iterations; [a..b] produces a closed interval (i.e. contains both end points), [a...b] gives you a half-open interval (i.e. b is not included). Similarly, this:

f(i) for i in a

变为：

var i, _i, _len;
for (_i = 0, _len = a.length; _i < _len; _i++) {
  i = a[_i];
  f(i);
}

同样，迭代次数是固定的，更改为 i

Again, the number of iterations is fixed and changes to i are overwritten.

如果你想在循环中搞乱数组和循环索引，那么你必须这样做手动使用和循环：

If you want to mess around the the array and the loop index inside the loop then you have to do it all by hand using a while loop:

i = 0
while i < arr.length
  if(sometimesTrue)
    arr.pop()
    --i
  ++i

或：

i = 0
while i < arr.length
  if(sometimesTrue)
    arr.pop()
  else
    ++i

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