kontrawize

Meat-loving cow found gobbling up chickens

Read about it here ...

Hand Luggage for Laptop and Camera

In the days before I had a laptop computer, I used to carry my photographic equipment as my hand luggage. After I joined the ranks of laptop owners, I suddenly found that I was no longer able to take my SLR with me on my travels.

However, I recently found the RoadWired Roadster Convertible. It's cabin luggage size, but has dividers for carrying your photographic equipment, and still has space for a laptop and accessories. It was a little difficult to get here in the UK (it took 2 months to arrive), but it's cleverly organised and seems quite well made. I hope to be travelling with it for some years to come.

Biometric passports - making identify theft easier for criminals and terrorists

Read the depressing news about the "security" (i.e. the lack thereof) of the new UK biometric passports. Are criminals paying to have these systems put together with such a lack of security? It makes me wonder sometimes.

Null propagation, part 2

There were some great comments on my discussion of null propagation in object-oriented languages, and how it would add a nice parallel to the way XPaths are evaluated. I wanted to discuss them a bit more.

John Cowan pointed out you couldn't just annotate a method to say "if this method is applied to a null, return null", because there are polymorphism issues that arise from that. I agree.

He also noted that you could raise an exception if certain methods try to return null, to stop the null result from having a further method applied to it. To my mind, that would actually be more work than just handling the null pointer exceptions, without gaining you anything.

Steven Lott suggested that the trick was to avoid nulls. If a method doesn't have a result, return a singleton "no result" object rather than a null. That avoids the null pointer exception issue. This is an interesting solution, and certainly completely implementable in the here-and-now. The only practical issue that I see is that it requires you to define a suitable "no result" singleton object for every class that needs null propagation, so that the result you return has the appropriate methods. The singleton objects would also need to be programmed specially so that they only return a "no result" object when a method is called on them. That said, if you are generating your code, this wouldn't be too hard to implement.

In retrospect, the behaviour I would like to see is slightly different again. It would only apply when you have layered method calls, e.g.

E result = a.b().c().d().e();

The idea would be that if a method is marked as a "null propagation" method, and its result is null, the sequence of method calls is be stopped immediately and a null is returned. So if method "c" returned a null, methods "d" and "e" would never be executed, and "result" would be set to null.

However, the code

C intermediate = a.b().c();
E result = intermediate.d().e();

would cause a null pointer exception (the value of "intermediate" is null) because null propagation doesn't apply if you store a value in a variable and then apply methods to it in a later statement.

Any reasons why this wouldn't work?

Opera is not a good IMAP client, part 2

I detailed with problems I've found with Opera as an IMAP e-mail client, basically that it doesn't refresh the IMAP folders (not for me, not for quite a few people according to the forums, may be related to particular IMAP mail servers). This means that you don't know whether you have new mail or not.

One way to refresh your list of IMAP messages in Opera is to close it down and start it up again. The alternative is to

• make sure your IMAP account is configured to "Include this account when checking manually";
• from the menu, select "Tools | Mail and chat accounts...";
• select your IMAP account in the "Manage accounts" dialog and press "Edit...";
• now just close the "Account Properties" dialog by pressing OK;
• close the "Manage Accounts" dialog;
• press the "Check/Send" button in the "Mail" sidebar.

Not ideal, but quicker than stopping and restarting Opera. That still leaves open the question of how you know when to check for new mail. I have a few work-arounds, none of them great:

• if you have Webmail for your account and it auto-refreshes, keep it open so that you know you have new mail;
• if you can connect from your PDA/phone to your e-mail account, and it refreshes properly, use that to see when new mail has come in (I use my Nokia E61 for this, and it flashes a light when new mail comes in);
• if your mail service provides an Atom/RSS feed (as Zimbra does), you can subscribe to that feed in Opera. Set it to update every 5 minutes, and you have a reasonable indication in Opera itself of when you have new mail.

These are just work-arounds, but they do make life a little easier if you have Opera IMAP issues, but aren't quite ready to switch to something else for your e-mail.

Null propagation

Via TheServerSide.net, I ran across a discussion of how to a discussion of how to do null propagation in C#. What is null propagation? Well, it means that if you evaluate an expression like

a.b().c().d().e()

and if any of the intermediate results is null, the result of the expression is null, without an exception being thrown. Normally, in Java/C#/etc., if (say) "a.b()" returned null, then "a.b().c()" would cause an exception when you tried to apply the method "c" to the null value returned by "a.b()".

Now, in many cases, this is exactly what you want, that your code throws an exception if an attempt is made to apply a method to a null value. So null propagation isn't a general principle that you would want to apply.

However, if you are working with XML, null propagation nicely reproduces the behaviour of XPath queries. If you do an XPath query like

/document/person/address

and there are no "<person> elements in the document, you get a null result, without any exception being thrown. If would be nice, sometimes, if you use a Java/C#/etc. expression like

document.getPerson().getAddress()

and just get a null result if any of the intermediate results is null. Of course, you could wrap this in one big try/catch block, but

• this makes the code more verbose and unreadable than you would want, since you have to do one try/catch block for every such expression
• exceptions tend to be expensive in code, OK for a few evaluations, but potentially significant for large numbers of evaluations.

How would you add null propagation to a language like Java/C#/etc.? Well, it strikes me there are two ways:

• wrap individual sections of code in some block construct that indicates a part of the code where null propagation should apply
• mark individual classes/methods/properties methods as being "null propagating". This could be done by adding support directly in the language, or it could be done (in Java/C# at least) by adding suitable annotations to the code, and then post-processing the compiled (virtual machine) code to add the necessary extra logic.

I think this would make XML processing code in Java/C# more readable and maintainable. What do you think?

Opera is not a good IMAP client

I've been using Opera for a long time now as my e-mail client. The partnership I work in, Miley Watts LLP, has been looking at Zimbra for a while as an e-mail and calendaring server, and we finally have that in place (via a hosted service, which is definitely the most painless way to go). Zimbra provides IMAP, so I looked forwards to migrating away from POP, and being able to maintain a hierarchy of mail folders on the mail server.

However, it turns out that Opera isn't a good enough IMAP client. The functionality is there, but what I've found is that Opera doesn't refresh its view of your IMAP folders unless you stop it and start it again. That makes it fairly useless. Sometimes you can get it to refresh by opening and closing the e-mail configuration dialog, but it isn't consistent, nor immediate, as a solution. Indeed, from the forums it is clear that many people have exactly the same problem, but some have different IMAP problems, so the issue may be to do with Opera's interactions with particular IMAP mail servers.

Whatever it is, it's very disappointing. None of the other other e-mail clients around seem to do as good a job as Opera does. I don't care a lot for Outlook (which doesn't run under Linux anyway), and Notes isn't great either. Evolution has a reputation for being slow and bloated, and one of my partners is telling me that Thunderbird's bugs are likely to drive him to using Outlook, even though he doesn't like it much either.

If Opera don't do something about this soon, and it's a pretty big issue, I'm going to be forced to switch, with all of the migration pain that goes with that. Ouch.

OpenOffice.org 2.0.4, Novell Edition, is available for Windows

The Novell Edition of OpenOffice 2.0.4 is available for download. The Novell Edition has enhanced Microsoft Office support as compared to "vanilla" OpenOffice (at least in principle, I don't have any definitive examples of this enhanced support in action).

This is an important update because it fixes some security issues. This updated version came out for (SUSE) Linux a while back, but the Windows releases lag behind.