jeudi 6 août 2015

Adding functionalities to existing classes in Scala

New functionalities can be added to existent classes by wrapping them with a Value class and adding and implicit methods for converting back and forward form the original class:

class TLong(val value: Long) {
  def +(other: TLong) = new TLong(value + otehr.value)
  def decrement =  new TLong(value - 1L)
  override def toString(): String = value.toString;
}

// implicit methods for conversions
implicit def toTLong(l: Long) = new TLong(l)
implicit def toLong(tl: TLong) = tl.value

// some tests
val l1: TLong = new TLong(1)
val l2: TLong = new TLong(2)
l1 + l2
1L + l2
l1 + 2L

From Scala 2.10, you can use implicit classes so that you don't have to define conversion methods as they are automatically created:
implicit class ImplicitLong(val l: Long) {
  def print = l.toString
}

1L.print

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