Scala FAQ: When you create a case class in Scala, a
copy method is generated for your case class. What does this
copy method do?
In short, it lets you make a copy of an object, where a “copy” is different than a clone, because with a copy you can change fields as desired during the copying process. The
copy method is important in functional programming, where values (
val) are immutable.
To demonstrate this, let's create an
Employee class as a case class:
scala> case class Employee(name: String, office: String, role: String) defined class Employee
Next, we'll create an instance of an
scala> val fred = Employee("Fred", "Anchorage", "Salesman") fred: Employee = Employee(Fred,Anchorage,Salesman)
Finally, we'll call the
copy method on
fred to create a new employee named
joe who has the same characteristics as the employee named
fred, but with a different name:
scala> val joe = fred.copy(name="Joe") joe: Employee = Employee(Joe,Anchorage,Salesman)
As you can see,
joe is a copy of
fred, but with a different name, which we changed during the
If you ever need to make a copy of an object in Scala, but not a clone, this gives you a little example of how the auto-generated
copy method on a Scala case class works.