Idiomatic Scala way to deal with base vs derived class field names?
- by Gregor Scheidt
Consider the following base and derived classes in Scala:
abstract class Base( val x : String )
final class Derived( x : String ) extends Base( "Base's " + x )
{
override def toString = x
}
Here, the identifier 'x' of the Derived class parameter overrides the field of the Base class, so invoking toString like this:
println( new Derived( "string" ).toString )
returns the Derived value and gives the result "string".
So a reference to the 'x' parameter prompts the compiler to automatically generate a field on Derived, which is served up in the call to toString. This is very convenient usually, but leads to a replication of the field (I'm now storing the field on both Base and Derived), which may be undesirable. To avoid this replication, I can rename the Derived class parameter from 'x' to something else, like '_x':
abstract class Base( val x : String )
final class Derived( _x : String ) extends Base( "Base's " + _x )
{
override def toString = x
}
Now a call to toString returns "Base's string", which is what I want. Unfortunately, the code now looks somewhat ugly, and using named parameters to initialize the class also becomes less elegant:
new Derived( _x = "string" )
There is also a risk of forgetting to give the derived classes' initialization parameters different names and inadvertently referring to the wrong field (undesirable since the Base class might actually hold a different value).
Is there a better way?
Edit: To clarify, I really only want the Base values; the Derived ones just seem necessary for initializing the Base ones. The example only references them to illustrate the ensuing issues. It might be nice to have a way to suppress automatic field generation if the derived class would otherwise end up hiding a base class field.
