如何安全地从for循环中的数组中删除项目? [英] How do I safely remove items from an array in a for loop?
问题描述
全部披露，这是一个作业问题:
Full disclose, this is for a homework question:
它应该具有[Circle]类型的私有属性.一组圆. 该方法应删除半径大于 最低要求，并且小于最高要求.
It should have a private property of type [Circle]. An array of circles. The method should remove any circles that have a radius larger than the minimum requirement, and smaller than the max requirement.
很明显，我应该使用removeAtIndex()删除不满足循环中确定条件的数组项.但是，由于我猜测是迭代器/索引不匹配"，因此许多人指出了删除循环中项目的危险.
It seems obvious that I should use removeAtIndex() to remove array items that don't meet a condition determined in the loop. However, many have pointed out before the perils of removing items in a loop because of what I guess is a "iterator/index mismatch".
最终我最终创建了一个空数组，并使用.append()将满足良好"条件的值推送到filteredCircles数组，但我忍不住感觉到这不符合要求分配标准.
Ultimately I ended up creating an empty array and using .append() to push the values that meet the "good" condition to a filteredCircles array, but I can't help but to feel that this this doesn't meet the criteria for the assignment.
有没有一种解决方案可以真正从循环中删除数组中的项?
Is there a solution that actually removes the items from the array in a loop?
推荐答案
如果FOR LOOP是非强制性的(并且我在引文中没有看到此要求)，则应使用filter方法.
If the FOR LOOP is not mandatory (and I don't see this requirement in the quoted text) you should use the filter method.
在数组上调用filter时，会得到一个新数组，其中仅包含确实符合传递给filter的闭包的值. 原始数组未突变.
When you invoke filter on an array you get a new array containing only the values that do respect the closure you passed to filter. The original array is not mutated.
struct Circle {
let radius: Double
}
let circles = [Circle(radius: 1), Circle(radius: 5.1), Circle(radius: 4), Circle(radius: 10.8)]
let bigCircles = circles.filter { $0.radius > 5 }
为什么这种方法比在FOR LOOP中修改数组更好
- 由于
circles是常量，因此您没有与多线程编程相关的问题.如果circles是可变的，那么当您循环它时，其他线程可能会对其进行更改，从而产生非常可怕的副作用. - 它不易出错.您不是在编写CPU应该做什么，而是在描述结果的样子.这样，您和编译器之间的潜在误会就更少了:)
- 您正在编写更少的代码，这意味着更少的潜在错误.
- Since
circlesis a constant, you don't have problems related to multithreading programming. Ifcircleswas mutable then other threads could change it while you are looping it with very scary side effects. - It's less error prone. You are not writing what the CPU should do, instead you are describing how the results should be. So less potential misunderstandings between you and the compiler :)
- You are writing less code which does mean less potential mistakes.
这些是编写函数式编程代码的一些好处.
These are some of the benefits of writing Functional Programming code.
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