dart - 在 Dart 中访问折叠/减少中的前一个元素

Question

不知能否重写这段dart代码:

 double length = 0;
 Point current = points.first;
 for (var next in points.skip(1)){
   length += current.distanceTo(next);
   current = next;
 }
 return length;

更简洁优雅的东西。我正在考虑使用 reduce/fold，但是有没有办法在组合函数中访问可迭代的先例元素？

Answer 1

使用函数式编程风格和 dart 扩展方法:

extension MyExtensions<T> on Iterable<T> {
  T foldByPairs(T initialValue, T combine(T value, T previous, T current)) {
    Iterator<T> iterator = this.iterator;
    iterator.moveNext(); // error handling omitted for brevity
    T value = initialValue;
    T previous = iterator.current;
    while (iterator.moveNext()) {
      T current = iterator.current;
      value = combine(value, previous, current);
      previous = current;
    }
    return value;
  }
}