Szathmáry László honlapja @ DEIK

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scala> val x = 5
x: Int = 5

scala> x.toString
res5: String = 5 // it's not shown in quotes but it's a String

scala> ""+x
res6: String = 5

scala> val s = "2015"
s: String = 2015

scala> s.toInt
res7: Int = 2015

scala> "scala".toInt
java.lang.NumberFormatException: For input string: "scala"
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
at java.lang.Integer.parseInt(Integer.java:580)
at java.lang.Integer.parseInt(Integer.java:615)
at scala.collection.immutable.StringLike$class.toInt(StringLike.scala:272)
at scala.collection.immutable.StringOps.toInt(StringOps.scala:30)
... 33 elided

toInt and toString are functions, but when calling them, the parentheses are missing. Why? The Scala style guide says the following:

"Omit empty parenthesis, only be used when the method in question has no side-effects (purely-functional). In other words, it would be acceptable to omit parentheses when calling queue.size, but not when calling println(). Religiously observing this convention will dramatically improve code readability and will make it much easier to understand at a glance the most basic operation of any given method. Resist the urge to omit parentheses simply to save two characters!"

So, if the function returns some value but doesn't change the object who called it, then you can omit the parentheses.

conversions