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POAvoiding Scala memory leaks - Scala constructors
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copied!<p>I was working through the "Programming in Scala" book, and was struck by a bit of a problem in the implementation of the class <code>Rational</code> in Chapter 6.</p> <p>This is my initial version of the <code>Rational</code> class (based on the book)</p> <pre><code>class Rational(numerator: Int, denominator: Int) { require(denominator != 0) private val g = gcd(numerator.abs, denominator.abs) val numer = numerator / g val denom = denominator / g override def toString = numer + "/" + denom private def gcd(a: Int, b: Int): Int = if(b == 0) a else gcd(b, a % b) // other methods go here, neither access g } </code></pre> <p>The problem here is that the field g remains for the lifetime of the class, even if never again accessed. This problem can be seen by running the following mock program:</p> <pre><code>object Test extends Application { val a = new Rational(1, 2) val fields = a.getClass.getDeclaredFields for(field <- fields) { println("Field name: " + field.getName) field.setAccessible(true) println(field.get(a) + "\n") } } </code></pre> <p>Its output is going to be: </p> <pre><code>Field: denom 2 Field: numer 1 Field: g 1 </code></pre> <p>A solution I found at the <a href="http://scala.sygneca.com//code/constructors" rel="noreferrer">Scala Wiki</a> involves the following: </p> <pre><code>class Rational(numerator: Int, denominator: Int) { require(denominator != 0) val (numer, denom) = { val g = gcd(numerator.abs, denominator.abs) (numerator / g, denominator / g) } override def toString = numer + "/" + denom private def gcd(a: Int, b: Int): Int = if(b == 0) a else gcd(b, a % b) // other methods go here } </code></pre> <p>Here, the field g is only local to its block, but, running the small test application, I found another field <code>x$1</code> which keeps a copy of the tuple consisting of <code>(numer, denom)</code>!</p> <pre><code>Field: denom 2 Field: numer 1 Field: x$1 (1,2) </code></pre> <p>Is there any way to construct a rational in Scala with the above algorithm, without causing any memory leaks?</p> <p>Thanks,</p> <p>Flaviu Cipcigan</p>

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