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POWhat is the performance impact of Scala implicit type conversions?
 

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  1. POWhat is the performance impact of Scala implicit type conversions?
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    <p>In Scala, is there a significant CPU or memory impact to using implicit type conversions to augment a class's functionality vs. other possible implementation choices?</p> <p>For example, consider a silly String manipulation function. This implementation uses string concatenation:</p> <pre><code>object Funky { def main(args: Array[String]) { args foreach(arg =&gt; println("Funky " + arg)) } } </code></pre> <p>This implementation hides the concatenation behind a member method by using an implicit type conversion:</p> <pre><code>class FunkyString(str: String) { def funkify() = "Funky " + str } object ImplicitFunky { implicit def asFunkyString(str: String) = new FunkyString(str) def main(args: Array[String]) { args foreach(arg =&gt; println(arg.funkify())) } } </code></pre> <p>Both do the same thing:</p> <pre><code>scala&gt; Funky.main(Array("Cold Medina", "Town", "Drummer")) Funky Cold Medina Funky Town Funky Drummer scala&gt; ImplicitFunky.main(Array("Cold Medina", "Town", "Drummer")) Funky Cold Medina Funky Town Funky Drummer </code></pre> <p>Is there any performance difference? A few specific considerations:</p> <p>Does Scala inline the implicit calls to the asFunkyString method?</p> <p>Does Scala actually create a new wrapper FunkyString object for each arg, or can it optimize away the extra object allocations?</p> <p>Suppose FunkyString had 3 different methods (funkify1, funkify2, and funkify3), and the body of foreach called each one in succession:</p> <pre><code>println(arg.funkify1()) println(arg.funkify2()) println(arg.funkify3()) </code></pre> <p>Would Scala repeat the conversion 3 times, or would it optimize away the redundant conversions and just do it once for each loop iteration?</p> <p>Suppose instead that I explicitly capture the conversion in another variable, like this:</p> <pre><code>val fs = asFunkyString(arg) println(fs.funkify1()) println(fs.funkify2()) println(fs.funkify3()) </code></pre> <p>Does that change the situation?</p> <p>In practical terms, is broad usage of implicit conversions a potential performance issue, or is it typically harmless?</p>
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    1. CO... and I'm singing: "♫♩♬ Why don't you just test it? ♫♩♬ Measure it? ♫♩♬ Do the one-million-times shuffle ♫♩♬"
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    2. COsince the difference between native and implicitly pimped code is so slow, can we now assume that scala does not create a new wrapper object for each call? Because somewhere else, that's what I heard, but I'm not sure. Would be interesting to get your other questions answered too...
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