Imported From: https://issues.scala-lang.org/browse/SI-4334?orig=1
Reporter: @Blaisorblade
See #5211

@Blaisorblade said:
Part of the problem might stem from the fact that the method

  protected final def Value: Value = Value(nextId)     

(declared [https://lampsvn.epfl.ch/trac/scala/browser/scala/tags/R_2_8_1_final/src//library/scala/Enumeration.scala#L131 here])
is not filtered out by populateNameMap:

    val methods = getClass.getMethods filter (m => m.getParameterTypes.isEmpty && classOf[Value].isAssignableFrom(m.getReturnType))

each of those methods is afterward invoked by populateNameMap; the Value method will then be invoked, it will construct an instance of Val, and the Val constructor will reset vsetDefined altering the return value of values (even if its definition seems immutable, it is not).
To complete the picture, populateNameMap is only called indirectly through Val.toString -> Enumeration.nameOf.

Problems:

1. The Val constructor should not reset vsetDefined, it should rather throw an exception if vsetDefined was true, i.e. values had been invoked.

2. populateNameMap should filter out Value, and a big fat warning should be added against adding new method with the same signature without fixing populateNameMap. Alternatively, populateNameMap could use getDeclaredMethods on the class of the actual enumeration, which filters out inherited methods.

3. Of course, this does not solve the fragility problem: if the Enumeration instance declares a method like randomElem(): Value, it will mistaken for an enumeration entry. As already asked, this "evil magic" should be documented.

Should I provide a patch for 1) and 2)?

@harrah said:
The immediate issue is a duplicate of #3687. I understand the general concern about Enumeration, but this should be discussed on the mailing lists. This subject has been discussed before, so you are most likely to succeed by understanding those discussions and giving concrete proposals. (I am not the final authority here- these are suggestions.)

@Blaisorblade said:
Sorry, my bad for this dup, and thank you very much for the helpful answer.