StackOverflow2013

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copied!<p><em>1) Can Method Handles be used for Function Types?</em></p> <p>Scala targets JDK 5 and 6 which don't have method handles, so it hasn't tried to deal with that issue yet.</p> <p><em>2) Can we get rid of the explicit declaration of "throws" type parameters?</em></p> <p>Scala doesn't have checked exceptions.</p> <p><em>3) Disallow @Shared on old-style loop index variables.</em></p> <p>Scala doesn't have loop index variables. Still, the same idea can be expressed with a certain kind of while loop . Scala's semantics are pretty standard here. Symbols bindings are captured and if the symbol happens to map to a mutable reference cell then on your own head be it.</p> <p><em>4) Handle interfaces like Comparator that define more than one method all but one of which come from Object</em></p> <p>Scala users tend to use functions (or implicit functions) to coerce functions of the right type to an interface. e.g.</p> <pre><code>[implicit] def toComparator[A](f : (A, A) => Int) = new Comparator[A] { def compare(x : A, y : A) = f(x, y) } </code></pre> <p><em>5) Specify mapping from function types to interfaces:</em></p> <p>Scala's standard library includes FuncitonN traits for 0 <= N <= 22 and the spec says that function literals create instances of those traits</p> <p><em>6) Type inference. The rules for type inference need to be augmented to accomodate the inference of exception type parameters.</em></p> <p>Since Scala doesn't have checked exceptions it can punt on this whole issue</p> <p><em>7) Elided exception type parameters to help retrofit exception transparency.</em></p> <p>Same deal, no checked exceptions.</p> <p><em>8) How are class literals for function types formed? Is it #void().class ? If so, how does it work if object types are erased? Is it #?(?).class ?</em></p> <pre><code>classOf[A => B] //or, equivalently, classOf[Function1[A,B]] </code></pre> <p>Type erasure is type erasure. The above literals produce scala.lang.Function1 regardless of the choice for A and B. If you prefer, you can write </p> <pre><code>classOf[ _ => _ ] // or classOf[Function1[ _,_ ]] </code></pre> <p><em>9) The system class loader should dynamically generate function type interfaces.</em></p> <p>Scala arbitrarily limits the number of arguments to be at most 22 so that it doesn't have to generate the FunctionN classes dynamically.</p> <p><em>10) Must the evaluation of a lambda expression produce a fresh object each time?</em></p> <p>The Scala specification does not say that it must. But as of 2.8.1 the the compiler does not optimizes the case where a lambda does not capture anything from its environment. I haven't tested with 2.9.0 yet.</p>

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