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POType-parametrized class with default type parameter
 

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    <p>For example, I have the following class hierarchy:</p> <pre><code>abstract class A { def a() {} def aa() } class B extends A { def aa() {} def b() } class C extends A { def aa() {} def c() } </code></pre> <p>And then I want to create a class that can store a collection of any combination of these classes instances. It will be able to call common methods. And due to type parametrization it must provide the ability to call class-specific methods if parametrized with these classes during the creation:</p> <pre><code>object Group { def apply(as: Buffer[A]) = new Group[A](as) def apply[T &lt;: A](as: Buffer[T]) = new Group[T](as) } class Group[T &lt;: A](as: Buffer[T]) { def a() { as.map(_.a()) } def aa() { as.map(_.aa()) } } </code></pre> <p>so the <code>Group</code> can be created with the default, most generic type parameter like this:</p> <pre><code>val groupA = Group(Buffer[A]()) groupA.a() //ok groupA.aa() //ok groupA.b() //error groupA.c() //error </code></pre> <p>and it can be created when parametrized explicitly with one of the descendants of <code>A</code>:</p> <pre><code>val groupB = Group[B](Buffer[B]()) groupB.a() //ok groupB.aa() //ok groupB.b() //ok groupB.c() //error </code></pre> <p>and if it is possible, I would like to somehow remove the unnecessary type specification of <code>[B]</code> when creating the group, since it can be extracted from the passed buffer type:</p> <pre><code>val groupB = Group(Buffer[B]()) </code></pre> <p>What is the correct way of realization of this functionality? Is it possible? Maybe there is a better architectural decision to accomplish this?</p> <p><strong>UPDATE:</strong> the code here is pseudocode, I just don't know how to write what I want.</p> <p><strong>UPDATE 2:</strong> I guess that calling type-specific methods like <code>b()</code> or <code>c()</code> should be realized through mapping:</p> <pre><code>groupC.as.map(_.c()) </code></pre> <p>which is <em>only</em> possible, if the type parametrization is correct. That gets closer to my idea, but the exact possible way of realization remains a mystery (aside from a bunch of usages of <code>asInstanceOf</code> things)..</p>
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    1. COMaybe use implicit conversion of your `Group[C]` to something that has a `c()` method, which is only applicable when the parameter is `C`?
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    2. CO@ziggystar: maybe, but could you please show an example of this? I am not sure I can grasp it like that.
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