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POScala: Making concrete classes of trait with type member that has a representation type
 

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    <p>This is a follow-up to a <a href="https://stackoverflow.com/questions/11236122/">previous question</a> where I had a trait <code>Garage</code> with a type member <code>CarType</code>, which itself had a type member <code>FuelType</code>, and I needed a function <code>refuel</code> that could take an instance of <code>CarType</code> as the first argument and an instance of the first argument's <code>FuelType</code> as the second argument.</p> <p>The answer, the two traits below, was to give <code>Car</code> a representation type <code>C &lt;: Car[C]</code>. The problem that I now have is that I can't figure out how to define the type parameter on the concrete classes implementing <code>Garage</code>, e.g. <code>ConcreteGarage</code> below.</p> <pre><code>trait Fuel trait Garage { type CarType &lt;: Car[CarType] def cars: Seq[CarType] def copy(cars: Seq[CarType]): Garage def refuel(car: CarType, fuel: CarType#FuelType): Garage = copy( cars.map { case `car` =&gt; car.refuel(fuel) case other =&gt; other }) } trait Car[C &lt;: Car[C]] { type FuelType &lt;: Fuel def fuel: FuelType def copy(fuel: C#FuelType): C def refuel(fuel: C#FuelType): C = copy(fuel) } class ConcreteGarage(val cars: Seq[ConcreteGarage#CarType]) extends Garage { type CarType = Car[CarType] // Nope //type CarType = Car[Any] // Nope //type CarType = Car[Nothing] // Nope //type CarType = Car[Car] // Nope //type CarType &lt;: Car[CarType] // Nope def copy(cars: Seq[CarType]) = new ConcreteGarage(cars) } </code></pre>
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