kotlinlang #announcements

@rafal: a Java Iterator has a remove method. Basically when you do a simple for loop and call remove on the collection inside the loop, you're breaking the iterator used by the for loop

ribesg

01/14/2016, 11:07 AM

Using Java Iterator's remove method doesn't break the iterator

ribesg

01/14/2016, 11:07 AM

Same for Kotlin's MutableIterator 😄

ribesg

01/14/2016, 11:08 AM

You may find this ugly but that's how you do it in Java 7-, there's no other way

rafal

01/14/2016, 11:08 AM

nice, the last time I directly used Interator was when I was writing some BlackBerry code running Java 1.4 or so 😛

rafal

01/14/2016, 11:08 AM

or maybe even 1.3

michaelrocks

01/14/2016, 11:09 AM

There’s an even more ugly way for removing items from

List

, which is used in some Android classes:

Copy code

for (int i = list.size() - 1; i >= 0; --i) {
  if (condition) {
    list.remove(i);
  }
}

kirillrakhman

01/14/2016, 11:09 AM

removing items from an arraylist will copy stuff around anyway, that's why

filter

won't be a big performance problem

ribesg

01/14/2016, 11:11 AM

@michaelrocks: looks less efficient than an Iterator I think

michaelrocks

01/14/2016, 11:11 AM

Yes, for

LinkedList

michaelrocks

01/14/2016, 11:12 AM

But I suppose it’s more efficient for

ArrayList

michaelrocks

01/14/2016, 11:12 AM

But I haven’t checked.

ribesg

01/14/2016, 11:13 AM

Yeah

ArrayList

would be different I guess. I'm not sure how it works, but at some point it will need to resize or something

kirillrakhman

01/14/2016, 11:14 AM

no resizing, but every delete except for the very last item will require copying items with a higher index around

kirillrakhman

01/14/2016, 11:14 AM

if you delete item 1 from 100, you will need to copy 99 items

jkbbwr

01/14/2016, 11:15 AM

Unless you used a different datastructure

kirillrakhman

01/14/2016, 11:15 AM

right

kirillrakhman

01/14/2016, 11:15 AM

this only applies to

ArrayList

jkbbwr

01/14/2016, 11:15 AM

but at the same time, why not lazy filter?

kirillrakhman

01/14/2016, 11:15 AM

exactly

kirillrakhman

01/14/2016, 11:16 AM

or even eager filter

kirillrakhman

01/14/2016, 11:16 AM

if you delete a lot, eager filtering will be very efficient

jkbbwr

01/14/2016, 11:16 AM

lazy filter is always more efficient

kirillrakhman

01/14/2016, 11:16 AM

not for small lists

kirillrakhman

01/14/2016, 11:16 AM

you need to instantiate a new sequence and access operations have more indirection