for Coffee循环使用范围

Question

Noob问题.我正在尝试用范围编写for循环.例如,这是我想用JavaScript生成的:

var i, a, j, b, len = arr.length;
for (i = 0; i < len - 1; i++) {
    a = arr[i];
    for (j = i + 1; i < len; j++) {
        b = arr[j];
        doSomething(a, b);
    }
}

到目前为止我最接近的是以下,但是

1. 它会生成不必要且昂贵的切片调用
2. 访问内部循环内的数组长度

CoffeeScript的:

for a, i in a[0...a.length-1]
    for b, j in a[i+1...a.length]
        doSomething a, b

生成的代码:

var a, b, i, j, _i, _j, _len, _len1, _ref, _ref1;

_ref = a.slice(0, a.length - 1);
for (i = _i = 0, _len = _ref.length; _i < _len; i = ++_i) {
  a = _ref[i];
  _ref1 = a.slice(i + 1, a.length);
  for (j = _j = 0, _len1 = _ref1.length; _j < _len1; j = ++_j) {
    b = _ref1[j];
    doSomething(a, b);
  }
}

(如何)可以用CoffeeScript表达？

Answer 1

基本上,将您的第一个JS代码转录到CS:

len = arr.length
for i in [0...len - 1] by 1
  a = arr[i]
  for j in [i + 1...len] by 1
    b = arr[j]
    doSomething a, b