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POScala macros and the JVM's method size limit
 

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    <p>I'm replacing some code generation components in a Java program with Scala macros, and am running into the Java Virtual Machine's limit on the size of the generated byte code for individual methods (64 kilobytes).</p> <p>For example, suppose we have a large-ish XML file that represents a mapping from integers to integers that we want to use in our program. We want to avoid parsing this file at run time, so we'll write a macro that will do the parsing at compile time and use the contents of the file to create the body of our method:</p> <pre><code>import scala.language.experimental.macros import scala.reflect.macros.Context object BigMethod { // For this simplified example we'll just make some data up. val mapping = List.tabulate(7000)(i =&gt; (i, i + 1)) def lookup(i: Int): Int = macro lookup_impl def lookup_impl(c: Context)(i: c.Expr[Int]): c.Expr[Int] = { import c.universe._ val switch = reify(new scala.annotation.switch).tree val cases = mapping map { case (k, v) =&gt; CaseDef(c.literal(k).tree, EmptyTree, c.literal(v).tree) } c.Expr(Match(Annotated(switch, i.tree), cases)) } } </code></pre> <p>In this case the compiled method would be just over the size limit, but instead of a nice error saying that, we're given a giant stack trace with a lot of calls to <code>TreePrinter.printSeq</code> and are told that we've slain the compiler.</p> <p>I have <a href="https://gist.github.com/travisbrown/5736883">a solution</a> that involves splitting the cases into fixed-sized groups, creating a separate method for each group, and adding a top-level match that dispatches the input value to the appropriate group's method. It works, but it's unpleasant, and I'd prefer not to have to use this approach every time I write a macro where the size of the generated code depends on some external resource.</p> <p>Is there a cleaner way to tackle this problem? More importantly, is there a way to deal with this kind of compiler error more gracefully? I don't like the idea of a library user getting an unintelligible "That entry seems to have slain the compiler" error message just because some XML file that's being processed by a macro has crossed some (fairly low) size threshhold.</p>
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    1. COThis question has been marked as ["already answered"](http://stackoverflow.com/q/6570343/334519), but what I'm asking is completely different from what is being asked in that question. I know that it's not possible to change the JVM's method size limit—I'm asking about workarounds and error handling in the context of Scala's new (2.10) macro system.
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    2. CONaively tried -optimise and 2.11 just sat there musing. Because my time on this earth is finite, I ctl-c'd. Maybe it will become obvious to me why this had to end badly.
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    3. CO@som-snytt: Interesting—same here, and no idea what that means. Without `-optimize`, 2.11.0-M3 does give a reasonable error message, at least.
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