Change List which is iterated over

Question

I heard that it is not good style to change a list which you are iterating over within the iteration.

Example (pseudo code):

for (int i = 0; i < someList.length(); i++) {
  someList.getAt(i).doSomething();
}

Why is that? Could there be any side effects?

This depends on the language, at least in part. – Blender Sep 17 '12 at 21:20 — Blender, Sep 17 '12 at 21:20

score 0 · Accepted Answer · edited May 23 '17 at 11:49

0

Make a copy. Change that, iterate around the original.

Otherwise the iterator won't know about changes made. More here:

edited May 23 '17 at 11:49

Community

answered Sep 17 '12 at 21:20

Paul Collingwood

score 0 · Answer 2 · answered Sep 17 '12 at 21:20

0

Something like this would be better.

for_each(E item in somelist)
{
     item.doSomeThing();
}

E/Item could be anything(customers, ints, doubles)

answered Sep 17 '12 at 21:20

what exactly is the advantage of for_each compared to for? – Michael Kohler Sep 17 '12 at 21:29
1

Well you do not have to call getAt(i) each time. This would speed things up a little more. – Sep 17 '12 at 21:33

2 Answers2