Instantiating Scala Type Members results in error

Quick question on why we can't instantiate type members? For example take this example:

abstract class SimpleApplicationLoader {
  type MyComponents <: BuiltInComponentsFromContext

  def load(context: Context) = {
    new MyComponents(context).application
  }
}

class SiteServiceApplicationLoader extends SimpleApplicationLoader {
  type MyComponents = SiteApplicationComponents
}

class SiteApplicationComponents(val context: Context) extends BuiltInComponentsFromContext(context) {
      ....
}

The SimpleApplicationLoader defines a type parameter MyComponents (upper bound to BuiltinComponentsFromContext). In the load method, the type parameter MyComponents is instantiated. SiteServiceApplicationLoader overrides the MyComponents type to _SiteApplicationComponents).

Anyway, the compiler gives the following error:

Error:(13, 9) class type required but SimpleApplicationLoader.this.MyComponents found
    new MyComponents(context).application

Just curious why type members cannot be instantiated? Any workarounds?

Thanks!

Solution

Operator new is only available for classes (or "like classes"). Type is not a class, so new is not available.

To instantiate an arbitrary type, a function could be used

def newMyComponents(context: Context): MyComponents

Update (thanks to @daniel-werner)

So the abstract class will look like

abstract class SimpleApplicationLoader {
  type MyComponents <: BuiltInComponentsFromContext

  def newMyComponents(context: Context): MyComponents

  def load(context: Context) = {
    newMyComponents(context).application    
  }
}

The abstract method might be implemented in the class where type is defined:

class SiteServiceApplicationLoader extends SimpleApplicationLoader {
  type MyComponents = SiteApplicationComponents
  def newMyComponents(context: Context): MyComponents = 
    new SiteApplicationComponents(context)
}