Well, you are saying that if you are using references to fact objects in combination with constraints comparing such a reference to some other object any (overridden) hashCode method must not refer to mutable fields of that object.
Certainly: this restriction should not hurt - I'm inclined to regard mutable hashCode methods as "suspicious" anyway.
But, nevertheless, it deserves a short paragraph in the "Expert" manual, don't you think so?
If I have
class Type {
int field;
setField( int f ){ field = f; }
}
and do
modify( $type ){ setField( 42 ) }
where is there a "nested accessor"?
$one: One()
$two: Two( $x: one == $one )
If you change a field on object "one". that field is a nested
accessor to Two.
one.field1 = "x"
is the same as doing
two.one.field1 = "x"
so to "two" changing the field of 1 is a nested accessor.
Think about how indexing works.
left == right
when two objects are == each other indexing creates a bucket for the
left and a bucket for the right. If you change the hashcode of the
one on the right, how will it find the bucket on the left?
Assume this: A is a field of B is a field of C is a
field of D is a...
Object references remain the same, in all objects; I
simply modify A, and
"when you change [A] you are also changing [B], so I
must notify the
engine for [B]" but that's a field of C... D... E...
and so on, until
'I' for infinity?!
It's just a change in some fact object's
hashCode that causes this problem.
If you don't want any indexing in your rule engine. If you
want indexing, you have to notify the engine. Changes to
nested accessors have always been invisible to the engine.
If a nested access changes, you must notify the engine of
the root fact.
Mark
-W
On 22 June 2011 22:37, Mark Proctor <mproctor@codehaus.org>
wrote:
> As One is a field of Two. When you change One you
are also changing Two, so
> you most notify the engine for Two too.
>
> MArk
> On 22/06/2011 14:37, Wolfgang Laun wrote:
>
> To avoid misunderstandings: yes, equals() is
written according to hashCode,
> i.e., according to the usual Java conventions.
>
> If
>
> - an object of class Two contains a member of
class One, and
> - one object Two and one object One are facts,
and
> - a rule modifies One, changing its hashCode
>
> then
>
> another rule containing the patterns
> $one: One()
> $two: Two( $x: one == $one )
>
> does NOT fire (any more).
>
> If you use the constraint
> one == $one || != $one
> the rule will fire, and you can observe that
hashCode results for $one and
> $x are the same and that $one.equals( $x )
returns true.
>
> Reproduced using 5.1.1 and 5.2.x
>
> -W
>
>
>
>
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