I want to define a trait named Ext
that renames the existing equals
method to equalsByAttributes
and defines a new equals
method at the same time. The trait is used
to extend case classes. My current solution looks somehow hacky:
case class A(id: Int) extends Ext
trait Ext { p: Product =>
// new implementation
override def equals(obj: Any) = obj match {
case that: AnyRef => this eq that
case _ => false
}
// reimplementation of old equals implementation
def equalsByAttributes(obj: Any) = obj match {
case that: Product =>
if (this.getClass.isAssignableFrom(that.getClass) || that.getClass.isAssignableFrom(this.getClass))
p.productIterator.toList == that.productIterator.toList
else
false
case _ => false
}
}
I wonder if there is a direct way to reference A
's equals
method in equalsByAttributes
so that one can avoid the reimplementation of this method?
Since there is a solution for referencing super implementations with super.METHOD_NAME
I thought there must be a similar syntax such as overridden.METHOD_NAME
for accessing specific implementations in the base class/trait that is going to be extended by the trait, so that my Ext
trait would look like this:
trait Ext { p: Product =>
override def equals(obj: Any) = ...
def equalsByAttributes(obj: Any) = overridden.equals(obj)
}
Do not change equals on case classes. If you need to do so, do not make your classes case classes. Changing case class methods will make the code behave unexpectedly (that is, unlike case classes), which will increase maintenance cost, break everything that assumes case classes work like case classes, make people's life miserable and get a lot of programmers to hate your guts.
In other words, it's not worth it. Don't do that.