Aladdin - Scala Bugtracking

	[#95]	project: compiler	priority: medium	category: bug
	submitter	assigned to	status	date submitted
	Matthias	Martin	fixed	2003-08-28 12:43:04.0
subject	Extending AnyVal, AnyRef, etc.
code	class C extends AnyVal;
what happened	The program compiles.
what expected	It should not be possible to inherit from AnyVal. I think we should enforce that all classes written in Scala are subclasses of scala.AnyRef. Alternatively, we could also require that all classes are either subclasses of scala.Object or they subclass a Java class.
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Changes of this bug report

Matthias edited on 2003-08-28 12:45:10.0

Martin edited on 2003-08-28 14:06:50.0

Matthias edited on 2003-09-01 01:13:07.0

I just re-opened the bug again, because the current fix is not sufficient. Currently, AnyVal is declared to be sealed. One implication of this is that it's not possible to subclass AnyVal. But it's still possible to subclass existing value classes like Byte, Short, Int, etc. These classes should be either final or at least sealed. Otherwise it's quite easy to crash the compiler. Here is an example:

class T extends Unit;

This yields the following exception:

{
  scala.Unit();
  scala.runtime.RunTime.box()
}
Exception in thread "main" java.lang.AssertionError
        at scalac.transformer.AddConstructors.transform(AddConstructors.java:211)
        at scalac.ast.Transformer.transform(Transformer.java:276)
        at scalac.ast.Transformer.apply(Transformer.java:67)
        at scalac.transformer.AddConstructorsPhase.apply(AddConstructorsPhase.java:42)
        at scalac.Global.compile(Global.java:266)
        at scalac.Global.compile(Global.java:245)
        at scalac.Main.main(Main.java:32)

Martin edited on 2003-09-02 18:57:31.0