Instantiate class with type parameters with the type of a variable in Scala

Question

I’ve got the following types

class Translator[To <: Language] { ... }
abstract class Language
object English extends Language
object German extends Language

Is there a way to instantiate Translator from a val that is either of type English or German?

I’m looking for something like the following (which doesn’t work):

val lang = if (someCondition) English else German
val translator = new Translator[classOf[lang]]

Nicolas · Accepted Answer · 2012-07-02 14:25:13Z

5

The issue is that neither English or German are classes. Are you sure that you need genericity here? Maybe composition is sufficient. A possible solution is:

val lang = Translator(if (someCondition) English else German)

with the following classes and objects:

case class Translator(l: Language)
trait Language
object English extends Language
object German extends Language

But it's a quite different design than the one you expected...

edited Jul 2, 2012 at 14:25

answered Jul 2, 2012 at 14:05

Nicolas

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3 Comments

pvorb Over a year ago

Thank you for the quick answer. Your second point was a mistake in my code. I fixed it. I just removed too much of the boilerplate to clarify my issue. I am not sure what the problem is with English and German not being classes.

Nicolas Over a year ago

Ok, I changed my answer accordingly. But the point is: is there a good reason to use generic types here ?

pvorb Over a year ago

You can’t know why I’m actually using generic types here. In my code every language has its own apply method, which itself has a generic type. This type defines a enumeration of Terms that can be translated by the Translator. So actually the Translator has a second type parameter, that applies to its apply method.

Johnny Everson · Accepted Answer · 2012-07-02 14:18:33Z

3

use the language as type argument in Translator constructor:

class Translator[To <: Language](lang:To) {...}
abstract class Language
object English extends Language
object German extends Language

new Translator(German)
res7: Translator[German.type] = Translator@8beab46

// using class instead of object:
class Italian extends Language
new Translator(new Italian)
res9: Translator[Italian] = Translator@6bc22f58

edited Jul 2, 2012 at 14:18

answered Jul 2, 2012 at 14:07

Johnny Everson

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1 Comment

pvorb Over a year ago

I prefer this answer since it still uses generic types.

drexin · Accepted Answer · 2012-07-02 14:55:01Z

0

Just instantiate Translator with the type of German or English like this:

new Translator[German.type]

edit:

or from a val

val x = German
new Translator[x.type]

edited Jul 2, 2012 at 14:55

answered Jul 2, 2012 at 14:35

drexin

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1 Comment

pvorb Over a year ago

The answer is correct but doesn’t answer my question (val).

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