Instantiating all classes that extend trait in Scala

Question

So I'm building a library, and the problem I have is as follows:

I have a trait, such as

package my.library
trait Animal {
  def randomFunctions
}

What I need to know is all the classes the consumer code has, that extend/implement said trait, such as

package code.consumer
case class Cat extends Animal
case class Dog extends Animal

So in summary: inside my library (which has the trait) I need to find out all classes (in consumer code) that extend/implement the trait.

So the trait will be in a library and the subclasses in a different library ? — Som Bhattacharyya, Mar 21 '16 at 08:31
The trait will be in a library, and the subclasses will be in the consumer code (?) — Lauri Lavanti, Mar 21 '16 at 08:33
As long as you import the library in the consumer code there should not be an issue. Or am i missing something ? — Som Bhattacharyya, Mar 21 '16 at 08:47
The problem is that I need to find out all the extending classes, that are in consumer code, inside the library — Lauri Lavanti, Mar 21 '16 at 08:49
Look here : http://stackoverflow.com/questions/34530694/get-all-the-classes-that-implments-a-trait-in-scala-using-reflection — Som Bhattacharyya, Mar 21 '16 at 08:57
@SomBhattacharyya that is close, but I would like to avoid using external libraries, and instead use the reflection API — Lauri Lavanti, Mar 21 '16 at 09:09
I see another one here : http://stackoverflow.com/questions/11053571/how-to-use-scala-reflection-api-to-get-all-contained-classes Have you tried searching existing questions? — Som Bhattacharyya, Mar 21 '16 at 09:31
I did search, but either the questions didn't answer my question directly enough, or seemed too complex for my need — Lauri Lavanti, Mar 21 '16 at 10:24
Is the answer for http://stackoverflow.com/questions/17490779/scala-reflection-loading-or-finding-classes-based-on-trait relevant? — Touko, Mar 21 '16 at 15:12

score 5 · Accepted Answer · answered Mar 31 '16 at 06:31

5

I finally solved this by using reflections (https://github.com/ronmamo/reflections) with the following little snippet:

val reflection = new Reflections()
reflection.getSubTypesOf(classOf[Animal])

answered Mar 31 '16 at 06:31

Lauri Lavanti

score 0 · Answer 2 · answered Mar 21 '16 at 14:00

0

An option would be to use a sealed trait. This forces all implementations of the trait to reside in the same file as the trait was defined.

This would break your separation of consumer and library code but you would be sure to get all implementations.

The only other option I can think of is to use an IDE, like IntelliJ which has an option to find all implementation based on given trait.

answered Mar 21 '16 at 14:00

Andreas Neumann

Unfortunately the separation of consumer and library code is quite necessary in this case – Lauri Lavanti Mar 22 '16 at 06:41

2 Answers2