Description
Aladdin: [http://scala-webapps.epfl.ch/bugtracking/bugs/displayItem.do?id=1293 bug 1293], [http://scala-webapps.epfl.ch/bugtracking/contribs/display.do?id=775 contrib 775]
== Code ==
The language specification has
"Method hashCode: ()int computes a hash-code depending on the data
structure in a way which maps equal (with respect to equals) values to equal
hash-codes."
This is only true if the hashCodes of constructor arguments have this property (see example below).
Some possible alternative wordings:-
"Method hashCode: ()int computes a hash-code depending on the data
structure in a way which maps equal (with respect to equals) values to equal
hash-codes, provided the hashCode methods of the data structure members each map equal
(with respect to equals) values to equal hash-codes."
"Method hashCode: ()int computes a hash-code. If the hashCode methods of the data structure members map
equal (with respect to equals) values to equal hash-codes, then the case class hashCode method does too."
object BadlyBehaved
{
var counter = 0
}
class BadlyBehaved
{
BadlyBehaved.counter = BadlyBehaved.counter + 1
override val hashCode = BadlyBehaved.counter
override def equals(rhs: Any) = rhs.isInstanceOf[BadlyBehaved]
}
case class CounterExample(b: BadlyBehaved) {}
val first = CounterExample(new BadlyBehaved())
val second = CounterExample(new BadlyBehaved())
assert(first.b == second.b)
assert(first.b.hashCode != second.b.hashCode)
assert(first == second)
assert(first.hashCode == second.hashCode, "Language Spec and implementation disagree") // FAILS== What happened ==
java.lang.AssertionError: assertion failed: Language Spec and implementation disagree== What expected ==