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POMaking my List.filter faster on Scala?
 

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  1. POMaking my List.filter faster on Scala?
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    <p>I'm making a game with Scala.</p> <p>My game has several pools for keeping enemies. They are immutable Lists because they are initialized to a size that should be enough (because creating new enemy instances during the game is very expensive).</p> <p>My game knows if an enemy is alive by asking <code>enemy.isVisible</code>. So my CollisionHandler works like:</p> <ol> <li>Combine all live enemies to a list</li> <li>Get live bullets</li> <li>Space partition these and do collision detection for bullets and enemies in the same space partition</li> </ol> <p>What supprised me was that according to the profiler, step 1 takes most of the time. And what that step does is basically say:</p> <pre><code>def allActiveEnemies = List(enemyType1.getAllActive, enemyType2.getAllActive, ... ).flatten </code></pre> <p>the <code>flatten</code> there doesn't seem expensive but instead it's get getAllActive calls. They are implemented in my Pooled trait like this:</p> <pre><code>trait Pooled[T &lt;: Entity] { var pool = List[T]() val INITIAL_POOL_SIZE:Int def initPool() { for(i&lt;-1 to INITIAL_POOL_SIZE) { addToPool(disable(createNew)) } } def getAllActive:List[T] = pool.filter(e =&gt; e.isVisible) } </code></pre> <p>(I omitted most of the trait because I don't think it's relevant here.)</p> <p>pool.filter is what burns like 45% of the total time spent in CollisionHandler, which seems really strange.</p> <p>Any suggestions to make things faster here?</p> <p>Maybe using ArrayLists instead of List? Maybe using some sorting and mutable collections? Or am I simply doing something horribly wrong?</p> <p>Thanks!</p>
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    1. COis `e.isVisible` a field access or a computation?
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    2. COisVisible is a getter for a field (as I'm using a Java based game engine as the basis of my game).
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    3. COI should probably add that I'm using Scala 2.8.1 and the game is run on Android 2.x
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