I have made heavy use of case classes in my code, replying on the underlying equality definitions of case class to behave correctly. Then now I found that I need to add another field member to a case class.
var
field member in case class, will it mess up the equality attributes for the case class? var
field value once, after that, no any reassignment will happen, before the case class goes into any collections or do equality comparison, will that still mess up the equality behaviors?Case class equality is based solely on its primary constructor attributes, whether they're var
or val
(yes, you can make them var
by giving an explicit var
to override the implied val
that case class constructor args possess.) Adding properties in the body of a case class
does not influence the compiler-generated equals(other: Any)
method.
Witness:
package rrs.scribble
object CCVarEq
{
case class CC1(i: Int, j: Float, var k: Double)
case class CC2(i: Int, j: Float, var k: Double) {
var l = math.Pi
}
def show {
val cc11 = CC1(1, 2.0f, 3.0)
val cc12 = CC1(1, 2.0f, 3.0)
val cc21 = CC2(1, 2.0f, 3.0); cc21.l = math.E
val cc22 = CC2(1, 2.0f, 3.0)
printf("cc11 == cc12: %s%n", cc11 == cc12); cc12.k = math.Pi * math.E
printf("cc11 == cc12: %s%n", cc11 == cc12)
printf("cc21 == cc22: %s%n", cc21 == cc22)
}
}
In the REPL:
scala> import rrs.scribble.CCVarEq._
import rrs.scribble.CCVarEq._
scala> show
cc11 == cc12: true
cc11 == cc12: false
cc21 == cc22: true
And all jamie's points about concurrency are valid, too.