Potential bug related to implicit conversions and overwritten methods

Implicit Views are not applied in this case because bc.someMethod denotes a member of BaseClass. Normal method overloading rules are used to select from the set of methods.

So basically, you can't add overloaded methods to an object using implicits.

-jason

"7.3 Views
Implicit parameters and methods can also define implicit conversions called views.
A view from type S to type T is defined by an implicit value which has function type
S =>T or (=>S )=>T or by a method convertible to a value of that type.
Views are applied in two situations.
...
2. In a selection e .m with e of type T , if the selector m does not denote a member
of T . In this case, a view v is searched which is applicable to e and whose result
contains a member named m. The search proceeds as in the case of implicit
parameters, where the implicit scope is the one of T . If such a view is found,
the selection e .m is converted to v (e ).m. "

On Sun, Jan 17, 2010 at 10:52 AM, Heiko Seeberger <heiko.seeberger@googlemail.com> wrote:

The implicit conversion is not applied. I guess this is a bug, because the two methods are different by signature. Or am I missing something?

2010/1/17 Jason Zaugg <jzaugg@gmail.com>

Implicit Views are not applied in this case because bc.someMethod denotes a member of BaseClass. Normal method overloading rules are used to select from the set of methods.

So basically, you can't add overloaded methods to an object using implicits.

Well, I can!
Adding a second method to RichClass ...
package object issue {   implicit def toRichClass(baseClass: BaseClass) = RichClass(baseClass)}
package issue {
  class BaseClass {     def someMethod(s: String) {}  }     case class RichClass(baseClass: BaseClass) {    // Does not work!    def someMethod(i1: Int, i2: Option[Int]) {}     // Works!!!    def someMethod(i: (Int, Option[Int])) {}  } }
... lets me call the second one without error:
scala> import issue._ import issue._
scala> val bc = new BaseClass bc: issue.BaseClass = issue.BaseClass@3082f392
scala> bc.someMethod((1, Some(2)))
So why does this one work?
Heiko
Work: weiglewilczek.com
Blog: heikoseeberger.name
Follow me: twitter.com/hseeberger
OSGi on Scala: scalamodules.org
Lift, the simply functional web framework: liftweb.net

It seems that the compiler allows adding overloads via Implicit Views that have the same arity as a method in the original type. I've raised a bug [1] with a simplified test and some analysis.

-jason

[1] https://lampsvn.epfl.ch/trac/scala/ticket/2913

On Sun, Jan 17, 2010 at 12:21 PM, Heiko Seeberger <heiko.seeberger@googlemail.com> wrote:

2010/1/17 Jason Zaugg <jzaugg@gmail.com>

Implicit Views are not applied in this case because bc.someMethod denotes a member of BaseClass. Normal method overloading rules are used to select from the set of methods.

So basically, you can't add overloaded methods to an object using implicits.

Well, I can!

Jason,
Thanks a lot.
Regarding the bug: Am I right guessing that it is more likely that the same airity thing will be "disable" in the future than the different airity thing will be enabled? Hence I should use another name for my methods to be safe?
Heiko

2010/1/17 Jason Zaugg <jzaugg@gmail.com>

It seems that the compiler allows adding overloads via Implicit Views that have the same arity as a method in the original type. I've raised a bug [1] with a simplified test and some analysis.

-jason

[1] https://lampsvn.epfl.ch/trac/scala/ticket/2913

On Sun, Jan 17, 2010 at 12:21 PM, Heiko Seeberger <heiko.seeberger@googlemail.com> wrote:

2010/1/17 Jason Zaugg <jzaugg@gmail.com>

Implicit Views are not applied in this case because bc.someMethod denotes a member of BaseClass. Normal method overloading rules are used to select from the set of methods.

So basically, you can't add overloaded methods to an object using implicits.

Well, I can!

--

Heiko

Work: weiglewilczek.com
Blog: heikoseeberger.name
Follow me: twitter.com/hseeberger
OSGi on Scala: scalamodules.org
Lift, the simply functional web framework: liftweb.net