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I am experimentin with Scala Macros, which are part of Scala 2.10, but as I try to compile (Using sbt) I get the following error:

[error] .../API.scala:9: not enough arguments for constructor OAuth:
(requestMethod: String, consumerSecret: String, consumerKey: String,
signatureMethod: String, version: String)jm.oauth.OAuth
[error]   private val oauth = new OAuth(OAuth.POST, oauthConsumerSecret,
oauthConsumerKey, OAuth.HMAC_SHA1)

You can find the implementation of the OAuth class here.

Is there any incompatibility between scala 2.10 and optional parameters?

The very same code, compiled with scala 2.9.1, worked perfectly.

mariosangiorgio
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  • I managed to have it work by recompiling the library containing `OAuth` with scala 2.10 RC2, but I'd like to have an explaination of what's going on as I may not always be able to recompile the code as I did. And I'd like to understand more because I am just curious :) – mariosangiorgio Nov 12 '12 at 00:15
  • Probably couldn't find the default parameter name when jumping between versions. Note that the constructor actually has five arguments and you were trying to get it to fill in the last (default) one. Not really an answer as to what's going on; more of a suggestion of where to start looking to understand it. – Rex Kerr Nov 12 '12 at 00:49

1 Answers1

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If you create a file containing only this class definition:

class Optional(x: Int = 0)

Then compile it with Scala 2.9.2 and run javap on the resulting class, you'll see this:

public class Optional implements scala.ScalaObject {
  public static final int init$default$1();
  public Optional(int);
}

Compile it again with 2.10.0-RC2 and javap it, and you get this instead:

public class Optional {
  public static int $lessinit$greater$default$1();
  public Optional(int);
}

So no, default arguments are perfectly fine in 2.10, you've just run into a concrete example of the lack of binary compatibility between major Scala versions.

Travis Brown
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    I'd say "the lack of binary compatibility between *major* Scala versions", like in 2.10.x vs 2.9.x. Minor releases are supposed to be source- and binary-compatible with their predecessors that belong to the same major release, e.g. 2.9.2 can be used instead of 2.9.1 without recompiling anything. – Eugene Burmako Nov 12 '12 at 05:36