| [#551] | project: compiler | priority: medium | category: bug | |
|---|---|---|---|---|
| submitter | assigned to | status | date submitted | |
| Burak | Martin | fixed | 2006-03-17 03:17:18.0 | |
| subject | ScalaRuntime._equals erroneous | |||
| code |
case class A(x:int); class B(x:int) extends A(x); |
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| what happened | The ScalaRuntime._equals method is called to test structural equality of case classes. It starts happily with (x.getClass() eq y.getClass()) && ... children equal to. Unfortunately, consider this: then B(3) should equal A(3), but it doesn't. |
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| what expected | Proper structural equality that follows inheritance. | |||
| [back to overview] | ||||
| Martin edited on 2006-03-17 19:46:55.0 |
| I am not sure. I think in this case we should pick the definition that is easier to spec. The current one reads: Two instances of case classes A(xs), B(ys) are equal if A == B and xs == ys. How do you spec the proposed change? And, what other motivation is there to change? -- Martin |
| Burak edited on 2006-03-17 22:29:44.0 |
|
oh, I was referring to the now outdated spec and was assuming that this part would not have changed. The right thing to do (spec and impl) is obviously "if (A <: B or B <: A) and xs==ys" where either A or B is a case class, then the instances are equal Surprise, this would then translate to the following code:
val xc = x.getClass();
val yc = y.getClass();
(xc.isAssignableFrom(yc) || yc.isAssignableFrom(xc)) && xs==ys
(I must admit that java.lang.Class method has a mystifying name) I can't recollect whether case classes participate in mixin composition. Depending on how we compile case classes, it might be necessary to go to a super-interface for that assignableFrom check (since a Scala class becomes a Java class and a Java interface). Otherwise, the equal method would not be symmetric. |
| Burak edited on 2006-03-17 22:36:07.0 |
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Answering "what other motivation", well to use the above method would prevent some existing code from breaking and would preserve the Liskov Substitution Principle(tm) : ) |
| Martin edited on 2006-05-27 11:34:39.0 |
| This is finally put to rest now. |