[Neo4j] TraversalDescription building hickup
Hi all, I just stumbled over the immutable TraversalDescription API (http://components.neo4j.org/neo4j-kernel/apidocs/index.html), which will not modify the object if you do TraversalDescription td = new TraversalDescriptionImpl(); td.depthFirst(); Instead, one needs to reassign td, like TraversalDescription td = new TraversalDescriptionImpl(); td = td.depthFirst(); However, TraversalDescription td = new TraversalDescriptionImpl().depthFirst(); will give you the expected td. IMHO this is unexpected behaviour and hard to get if you just follow the common fluent API and presume a Builder-pattern. Especially since no errors are thrown and you just end up with strange results and unreachable code i e.g. a custom PruneEvaluator etc. True, the API says it is immutable, but still I think this is hard. WDYT? Should we think of changing this to a proper builder.modify().modify etc and finally builder.build() wich gives you the final, immutable instance of TraversalDescription and is clearly understandable by clients? Cheers, /peter neubauer COO and Sales, Neo Technology GTalk: neubauer.peter Skype peter.neubauer Phone +46 704 106975 LinkedIn http://www.linkedin.com/in/neubauer Twitter http://twitter.com/peterneubauer http://www.neo4j.org - Your high performance graph database. http://www.thoughtmade.com - Scandinavia's coolest Bring-a-Thing party. ___ Neo4j mailing list User@lists.neo4j.org https://lists.neo4j.org/mailman/listinfo/user
Re: [Neo4j] TraversalDescription building hickup
2010/7/27 Peter Neubauer peter.neuba...@neotechnology.com Hi all, I just stumbled over the immutable TraversalDescription API (http://components.neo4j.org/neo4j-kernel/apidocs/index.html), which will not modify the object if you do TraversalDescription td = new TraversalDescriptionImpl(); td.depthFirst(); Instead, one needs to reassign td, like TraversalDescription td = new TraversalDescriptionImpl(); td = td.depthFirst(); However, TraversalDescription td = new TraversalDescriptionImpl().depthFirst(); will give you the expected td. IMHO this is unexpected behaviour and hard to get if you just follow the common fluent API and presume a Builder-pattern. Especially since no errors are thrown and you just end up with strange results and unreachable code i e.g. a custom PruneEvaluator etc. True, the API says it is immutable, but still I think this is hard. WDYT? Should we think of changing this to a proper builder.modify().modify etc and finally builder.build() wich gives you the final, immutable instance of TraversalDescription and is clearly understandable by clients? I still think the current approach is more useful (although it'd be nice with more input on this). One reason I think it's better is that you can half-bake descriptions as private static final or similar and then complete the descriptions in several different places in your code. You can even pass in descriptions in methods and what not, without any risc of them being modified. I think javadoc should better explain this and it should be expected that developers read javadoc, right? Cheers, /peter neubauer COO and Sales, Neo Technology GTalk: neubauer.peter Skype peter.neubauer Phone +46 704 106975 LinkedIn http://www.linkedin.com/in/neubauer Twitter http://twitter.com/peterneubauer http://www.neo4j.org - Your high performance graph database. http://www.thoughtmade.com - Scandinavia's coolest Bring-a-Thing party. ___ Neo4j mailing list User@lists.neo4j.org https://lists.neo4j.org/mailman/listinfo/user -- Mattias Persson, [matt...@neotechnology.com] Hacker, Neo Technology www.neotechnology.com ___ Neo4j mailing list User@lists.neo4j.org https://lists.neo4j.org/mailman/listinfo/user
Re: [Neo4j] TraversalDescription building hickup
I may have missed your point. But, FWIW, this model reflects what I would
expect from an immutable object.
For example:
String s = Test;
s.replace('T', 't'); // s still contains Test
BigInteger and Date are the same way.
-Paul
-Original Message-
From: user-boun...@lists.neo4j.org [mailto:user-boun...@lists.neo4j.org] On
Behalf Of Mattias Persson
Sent: Tuesday, July 27, 2010 2:41 PM
To: Neo4j user discussions
Subject: Re: [Neo4j] TraversalDescription building hickup
2010/7/27 Peter Neubauer peter.neuba...@neotechnology.com
Hi all,
I just stumbled over the immutable TraversalDescription API
(http://components.neo4j.org/neo4j-kernel/apidocs/index.html), which
will not modify the object if you do
TraversalDescription td = new TraversalDescriptionImpl();
td.depthFirst();
Instead, one needs to reassign td, like
TraversalDescription td = new TraversalDescriptionImpl();
td = td.depthFirst();
However,
TraversalDescription td = new TraversalDescriptionImpl().depthFirst();
will give you the expected td.
IMHO this is unexpected behaviour and hard to get if you just follow
the common fluent API and presume a Builder-pattern. Especially since
no errors are thrown and you just end up with strange results and
unreachable code i e.g. a custom PruneEvaluator etc. True, the API
says it is immutable, but still I think this is hard.
WDYT?
Should we think of changing this to a proper builder.modify().modify
etc and finally builder.build() wich gives you the final, immutable
instance of TraversalDescription and is clearly understandable by
clients?
I still think the current approach is more useful (although it'd be nice
with more input on this). One reason I think it's better is that you can
half-bake descriptions as private static final or similar and then complete
the descriptions in several different places in your code. You can even pass
in descriptions in methods and what not, without any risc of them being
modified. I think javadoc should better explain this and it should be
expected that developers read javadoc, right?
Cheers,
/peter neubauer
COO and Sales, Neo Technology
GTalk: neubauer.peter
Skype peter.neubauer
Phone +46 704 106975
LinkedIn http://www.linkedin.com/in/neubauer
Twitter http://twitter.com/peterneubauer
http://www.neo4j.org - Your high performance graph database.
http://www.thoughtmade.com - Scandinavia's coolest Bring-a-Thing party.
___
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https://lists.neo4j.org/mailman/listinfo/user
--
Mattias Persson, [matt...@neotechnology.com]
Hacker, Neo Technology
www.neotechnology.com
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Re: [Neo4j] TraversalDescription building hickup
I think the key point of Peters request is to separate the 'builder' from
the 'traverser'. Mattias argument appears to state that if the builder and
traverser are the same class (series of immutable instances of the same
class), you have more flexibility in refactoring, because you don't have to
remember to convert to the traverser as the last step (Peter called build()
as the last step of a builder creating a 'really immutable' traverser).
The example of String.replace is similar to Mattias description, one
immutable object creating another instance of the same class. However, I
personally think Peter has a point. Keeping the builder and traverser as two
separate objects might force the coder to make a clear decision about when
the traverser should no longer be modified. Once the build() method is
called, we are done. Before that point the developer still has complete
flexibility to modify the traversal rules multiple times in as many steps
and places in the code they want, but once they call build(), the returned
traverser cannot be modified at all.
Despite my argument above favouring Peters approach, I actually do not have
a strong opinion on this, and think both ways are good. I confess that had I
coded this myself there is a good way I would have done it with one class
like Mattias describes.
(and I just realized another thing, we normally access traversers in
for(Iterable) loops that call iterator(), which itself returns a 'really
immutable' object, so perhaps adding another in the chain is overkill :-)
On Tue, Jul 27, 2010 at 9:00 PM, Paul A. Jackson paul.jack...@pb.comwrote:
I may have missed your point. But, FWIW, this model reflects what I would
expect from an immutable object.
For example:
String s = Test;
s.replace('T', 't'); // s still contains Test
BigInteger and Date are the same way.
-Paul
-Original Message-
From: user-boun...@lists.neo4j.org [mailto:user-boun...@lists.neo4j.org]
On Behalf Of Mattias Persson
Sent: Tuesday, July 27, 2010 2:41 PM
To: Neo4j user discussions
Subject: Re: [Neo4j] TraversalDescription building hickup
2010/7/27 Peter Neubauer peter.neuba...@neotechnology.com
Hi all,
I just stumbled over the immutable TraversalDescription API
(http://components.neo4j.org/neo4j-kernel/apidocs/index.html), which
will not modify the object if you do
TraversalDescription td = new TraversalDescriptionImpl();
td.depthFirst();
Instead, one needs to reassign td, like
TraversalDescription td = new TraversalDescriptionImpl();
td = td.depthFirst();
However,
TraversalDescription td = new TraversalDescriptionImpl().depthFirst();
will give you the expected td.
IMHO this is unexpected behaviour and hard to get if you just follow
the common fluent API and presume a Builder-pattern. Especially since
no errors are thrown and you just end up with strange results and
unreachable code i e.g. a custom PruneEvaluator etc. True, the API
says it is immutable, but still I think this is hard.
WDYT?
Should we think of changing this to a proper builder.modify().modify
etc and finally builder.build() wich gives you the final, immutable
instance of TraversalDescription and is clearly understandable by
clients?
I still think the current approach is more useful (although it'd be nice
with more input on this). One reason I think it's better is that you can
half-bake descriptions as private static final or similar and then complete
the descriptions in several different places in your code. You can even
pass
in descriptions in methods and what not, without any risc of them being
modified. I think javadoc should better explain this and it should be
expected that developers read javadoc, right?
Cheers,
/peter neubauer
COO and Sales, Neo Technology
GTalk: neubauer.peter
Skype peter.neubauer
Phone +46 704 106975
LinkedIn http://www.linkedin.com/in/neubauer
Twitter http://twitter.com/peterneubauer
http://www.neo4j.org - Your high performance graph
database.
http://www.thoughtmade.com - Scandinavia's coolest Bring-a-Thing party.
___
Neo4j mailing list
User@lists.neo4j.org
https://lists.neo4j.org/mailman/listinfo/user
--
Mattias Persson, [matt...@neotechnology.com]
Hacker, Neo Technology
www.neotechnology.com
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