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    <p>THe following is a bit of a departure from the way you have coded your <code>Printer</code>, but potentially could fulfil your intentions. Note that this way of coding your class enables a greater separation of concerns: you can define filters and print implementations (the <code>doPrint</code> argument) independently of how they are being used:</p> <pre><code>case class Printer[T](val filters: List[Function1[T, Boolean]], val doPrint: T =&gt; Unit) { def print(t: T): Unit = { if (filters.forall(_(t))) doPrint(t) } def addFilter[TT &lt;: T](f: TT =&gt; Boolean): Printer[TT] = copy(f :: filters) } </code></pre> <p>Note that I haven't needed to specify contravariancy here, not sure if that will be an issue for you.</p> <p>To use the class, you don't need to subclass, just pass suitable arguments into the constructor (actually, the companion <code>apply</code> factory method provided for free for case classes) - eg:</p> <pre><code>case class Foo(x: Int) val fooChk1: Foo =&gt; Boolean = (f: Foo) =&gt; f.x != 1 val fooPrinter1 = Printer(fooChk1 :: Nil, (f: Foo) =&gt; println(s"Foo: x = ${f.x}")) val fooChk3: Foo =&gt; Boolean = (f: Foo) =&gt; f.x != 3 val fooPrinter2 = fooPrinter1.addFilter(fooChk3) val foo3 = Foo(3) fooPrinter1.print(foo3) // Prints 'Foo: x = 3' fooPrinter3.print(foo3) // Prints nothing </code></pre> <p>There is also a fair bit of scope for using implicits here, too - both for parameters to <code>Print</code> (eg. change the constructor to <code>(val filters: List[Function1[T, Boolean]])(implicit val doPrint: T =&gt; Unit)</code>), and for specific <code>Print[X]</code> variants.</p>
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    1. COGood example. I don't think it quite works for me. I use the subclassing because the functionality is often quite complicated and I create instances of the subclasses specified in a DSL using reflection.
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    2. COThinking about it more, separation of concerns might be my problem. Maybe I'll make a `ConstraintedPrinter[T](printer: Printer[T], filters: Seq[T => Boolean])`.
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