Android studio often suggests me that I can use st...

# announcements

[haxpor]

Android studio often suggests me that I can use stdlib operation i.e. filter{}, map{} over normal loop code. Yes, I like to use those. But peek into the code from IDE reveals that actually filter{} is not better than normal loop as it dynamically creates a new ArrayList object to hold filtered elements. So normal loop would slightly has better performance.

My question is as IDE suggests me like this
- Is the performance that significant (although I can’t feel any difference)?
- Is there anyone already did performance test comparing between filter{}, map{} etc against normal way?
- Should I always use lambda functions as also suggested by IDE? (I want to but from above, I didn’t feel safe)

[marstran]

haxpor: With your loop, do you filter it in place or something? Is it mutable?

[haxpor]

I captured the screen for the code before I changed them all to normal loop. It looks like this https://pbs.twimg.com/media/DEqGVA3VwAA-I7a.jpg:large

[haxpor]

I don’t think it’s in-place, it return new array for forEach as I peeked in. Any idea, or suggestion?

[marstran]

Ok, I think would do something like this:

flyingSaucers.filter { !it.shouldBeRemoved }
             .flatMap { it.bullets }
             .filter { !it.shouldBeRemoved && player.contains(it.x, it.y) }
             .forEach {
                 it.shouldBeRemoved = true
                 player.hit()
                 Game.res.getSound("explode")?.play()
             }

[marstran]

Yes, it does. With your loop, did you just check everything with if-tests? You didn't create a new filtered list there?

[marstran]

Anyway, this should really be a performance problem. You shouldn't really care about this unless it actually becomes a problem. Premature optimization is the root of all evil as they say 😉

[marstran]

I would move that Game.res.getSound("explode") outside the loop though.

[haxpor]

Thanks, I understand it might be premature. But are you sure it’s in-place?

[marstran]

No, it is not in place. I was wondering what you did with your loops.

[haxpor]

Ohh, I see. Yup.

[haxpor]

I need to filter and do a certain task with it; only for those that is not marked to be removed soon yet.

[haxpor]

Thanks, I love to use those stuff, but this thing bugs me from time to time.

[haxpor]

Thanks for editing the code, I will keep an eyes on flatMap when possible.

[marstran]

You could convert it to a sequence with .asSequence() to make it lazy though, but I'm not really sure if it would make a difference here.

[haxpor]

still filter will require to create ArrayList to hold result, but asSequence() is better too I think.

[haxpor]

seem I cannot avoid object creation there before doing anything useful inside the loop

[marstran]

It could be that the JIT will optimize it away even. It shouldn't be a problem.

[haxpor]

I totally didn’t think about takeIf or takeUnless, so I can combine forEach with takeIf without creating new object in filter before going into the loop.