"Clean coal" technologies being researched, says EU Energy Commisioner

Andris Piebalgs, EU's Energy Commisioner said in a speech at the eBio General Assembly yesterday:

From the point of view of security of supply, coal is a wonderful source of energy. Europe has plenty of coal; outside Europe, reserves are spread widely. But the greenhouse gas performance of coal is worse than that of any other fuel.
"Clean coal" technologies are being developed to solve this problem. We will accelerate research into these technologies, and take other steps to create a market for them. But there is no chance of their making a significant contribution by 2020.

That's interesting. EU is under a rather heavy pressure to lessen its energy dependency on oil and gas from Russia, and living in a country that got some collateral damage from the last muscle flexing of russian energy monopoly I can completely understand that. But going back to coal burning, hoping that its ecologically disastrous side effects can be eliminated by some not-yet-existing, but presumably researched "clean coal" technologies is a bit worrisome. I mean, as far as I know, you just can't burn coil without getting CO2, since "burning" by definition is "oxydating". At best, those "clean coal" technologies might try to somehow further process that CO2, instead of emitting it into the environment. I'm admittedly a bit skeptical about it, but I definitely welcome any sufficiently rigorous scientific research into the issue.

Java puzzler: field hide-and-seek

Someone recently asked me to explain the rules for field access in Java, and it sparked the little test program you see below. Can you guess the number sequence it prints?

class Class1 {
   String data;
    
    Class1(String data) {
        this.data = data;
    }

   String getData() {
        return this.data;
    }
}

class Class2 extends Class1 {
    String data;

    Class2(String data, String superData) {
        super(superData);
        this.data = data;
    }
}

public class Test {
    public static void main(String[] args) {
        Class1 obj1 = new Class1("1");
        Class2 obj2 = new Class2("2", "3");

        System.out.println(obj1.data);
        System.out.println(obj2.data);
        System.out.println((false ? obj1 : obj2).data);

        System.out.println(obj1.getData());
        System.out.println(obj2.getData());
        System.out.println((false ? obj1 : obj2).getData());
    }
}

It goes to show three interesting things (which are perfectly logical, we just don't think about them often):

• compile-time type of the ?: expression is the most specific common supertype of the compile-time types of its two target subexpressions,
  
• selection of target type for field access happens at compile time (no "virtual fields" in Java),
  
• compile-time type of "this" expression is the class that declares the method,

Remember folks, avoid both field hiding and direct access to fields in the first place, so your code doesn't become a puzzler :-)

What did D'Anna see?

(Listening to the BSG Season 2 soundtrack CD as I write this, of course. Package from Amazon arrived yesterday, woot).

Might as well dedicate another post to BSG... I'll admit it feels a bit strange to discuss a plot of a television series here (actually, it feels strange for me to be this enthusiastic about any TV show) but the thing is that this particular damn show actually provokes thoughts, touching with very good sense upon questions ranging from politics to religion to ability of nonhuman beings (I'm avoiding the term "artificial intelligence") to have what unsettingly resembles human minds - sentient, free willed, emotional, even religious.

Anyway, if you didn't see the last BSG episode, "Rapture", you might as well stop reading now, because it won't make any sense to you then.

In the last episode, D'Anna supposedly saw the faces of the last five cylon models in the temple of the Jupiter during the supernova breakout before she died her current body terminally malfunctioned. But did she really see them?

I have a suspicion that as much as it seems so on the surface of it, she actually didn't. If you remember, the Leoben instance that Adama encountered at the weapon storage station in the series pilot mentioned that his nervous system is negatively affected by the electromagnetic activity in the cloud that surrounds the station. I can only imagine how can an ongoing supernova breakout affect the nervous system of a humanoid cylon exposed to it standing on the surface of a nearby planet. So, yes, it might as well be that D'Anna hallucinated as a mental malfunction (and later physical too) caused by the supernova burst and just saw what her subconscious (assuming they have an analogous layer in their psyche) wanted her to see.

Further supporting this claim is that the other cylons don't think much about D'Anna's messiastic fixation and pragmatically only see it as a danger to their common goals. Also, thinking outside of the story, I see that the series writers don't stack unsolved mystery upon unsolved mystery as a means of driving the plot forward (fortunately, unlike Lost's writers, who pretty much seem to be lost in the plot, and definitely lost me as a viewer - pun fully intended), and in accordance to this, nothing else even hints that her mystical beliefs could be true. Well, except that the location where she saw the last five in her vision was the same location Baltar saw in his vision on Kobol at the end of season one. This could be explained if the location is something buried in minds of all cylons, and either Baltar is a cylon himself or the Six in his head is more than just a hallucination that suppresses his sense of guilt. Neither of these assumptions are provable based on currently available information though, but I believe latter is vastly much more probable than the former.

Oh, and there's some wonderful yin-yang contrast in how it's Cavil, the only atheist model among cylons who informs the religious, messisatically predisposed D'Anna that the rest of the community has sentenced her to being boxed in cold storage. I also don't have a moment's doubt that in the future of the series, Baltar will somehow get in a situation where he can restore her from cold storage into a body, and won't hesitate for a moment, as he believes she has the answer to his burning identity-crisis question.

Microsoft to the rescue of the mankind

(click on the link to see the original flash animated ad). It's not a fake - this ad was indeed published by Microsoft and for a while appeared on Battlestar Galactica's official homepage on Sci-Fi channel.

Related fun fact: Did you know no TV channel carries Battlestar Galactica in Hungary? One of the commercial chanells bought the rights for the first season few years ago, but they stopped broadcasting it after only (I think) six episodes, citing poor viewer ratings. Morons. (Someone was a moron. Either the TV channel producers, or the company measuring the viewership ratings, or, err..., the local TV audience.) If it weren't for BitTorrent, I wouldn't be able to watch it at all. (And I also wouldn't have any motivation to buy the mini series + the first two seasons on DVD + all the soundtrack CDs from Amazon either, which I did recently. So much for studios' fairytale of "lost revenue due to copyright infringement by file-sharing".)

Graz for geeks

Wife and me spent the few days around New Year in Graz, Austria. I've taken 245 pictures in total, and now published 13 of them on my Flickr page. I published only those though that have some geek appeal. Among the stuff is Graz's new palace of arts, a building resembling an alien spaceship complete with a "Resistance is futile" neon sign and pulsating lights, a snowman sculpture similar to Calvin's snowman art, half a millenium old clockwork, sculpture carrying the first Austrian cosmonaut's message encoded in waltz steps (no kidding) and more.

Java garbage collection analyzer

IBM Pattern Modeling and Analysis Tool for Java Garbage Collector is "a tool that parses verbose GC trace, analyzes Java heap usage, and recommends key configurations based on pattern modeling of Java heap usage".

I remember I heard about a similar tool for HP JVM on HP-UX (I think Kirk Pepperdine told me about it on the train from Aarhus to Copenhagen this October when we were travelling home from JAOO) - it'd collect GC statistics and then provide you with a GUI where you could play with sliders for various memory settings, and it'd calculate how would have the GC behaved if the program was run with those settings.

On a somewhat related note, as someone who had to do some ammount of GC tuning in the past, I'll be curious about experiences people have with Java 6's GC that is said to behave optimally in most situations without any manual tuning... It sounds enthusiastic, but I'm too often reminded that in reality there is no silver bullet in automatic memory management.

No H.264 playback on Sony Ericsson W850?

My new gadget, the Sony Ericsson W850, is able to play back video (in addition to being able to record video, take photos, play music, and only incidentally, to make phone calls). It has a 320x240 screen (same as gen-5 iPod), and according to its freely available tech specs, supports "MPEG-4 Simple Visual Profile Level 0, H.263, H.264 Baseline Profile Level 1". My experience though is that it can't play back H.264, at least it didn't play back anything I could produce. I tried both encoding a few minutes clip from a DVD using Handbrake, as well as converting another few minutes DivX clip using iSquint, and the results are the same with both: I tried every combination of settings in both programs, and the combinations where vanilla MPEG-4 is used result in a video file that plays okay on the phone, and the combinations where H.264 is used result in a video file that results in a black screen on the phone (although the audio plays okay).

I have to stress that I'm not saying the device doesn't play H.264. I'm just saying that several video files converted by the above two programs with H.264 option selected didn't play. I could've run into some profile capability violation or something similar - I'm not that much knowledgeable in video encoding. Some people say I should try experimenting with command line ffmpeg. Honestly, I won't. It's not that important, really. While I can find time to listen to music on the go, I really can't imagine I'll want to watch any video content squinting at the 2" screen. The ammount of time I decided to invest in this went only so far as to try comfortable GUI options, with motivation being "because it was there." If anyone has more success than me though, please let me know.

Another kludge in Java - varargs

Varargs in Java. Seriously, who needed this?

You're probably aware of my position on Java Generics, how I view their implementation to be a horrific kludge, a compromise made in name of backward compatibility where the backward compatibility issues are in fact nonexistent.

Now, here's a new discovery - vararg methods. Someone asked on the Rhino list whether we can support them, and I answered that as long as he passes the vararg argument explicitly as an array, then yes. I decided to investigate the problem further within a codebase I'm truly familiar with - FreeMarker's BeansWrapper. I quite quickly came up with a scheme for supporting non-overloaded vararg methods. However, for overloaded ones, the exercise becomes, shall we say, a bit more involved. As I had to discover, the overloaded method resolution algorithm from Java Language Specification (JLS) 2nd edition was seriously overwritten into a three-stage algorithm in JLS 3rd edition, of which the "old" (mathematically quite elegant) algorithm from JLS 2 became the second stage. I probably need some additional time to grasp it, but it looks quite horrible now. If you wish, compare:

"Method Invocation Expressions" section in JLS 2 

with

"Method Invocation Expressions" section in JLS 3.

Of course, the chapters regarding type conversions (required, as overloaded method resolution relies on the definition of "method invocation conversions", a subset of conversions that is allowed between actual and declared parameter types when invoking a method) are also substantially rewritten to cope with boxing, unboxing, and generic types.

And the worst part? Varargs are yet another Java the Language feature implemented without a Java the Virtual Machine support. They're purely syntactic sugar, with vararg argument being an array on bytecode level. Several annoying things:

1. reflection is unaware of it. You can't just pass more arguments to the method, you have to pass the vararags arguments in an explicitly allocated array.
   
2. No automatic object-to-primitive conversion when using reflection. If the vararg method's type is "int...", you must pass int[], not an Integer[]. Compare this with automatic 
   conversion for regular argument types.
3. Unintuitive behaviour. Quick, should the following example print 1 or 0:

public class Test {
  static void x(Object... i) {
    System.out.println(i.length);
  }
  public static void main(String[] args) {
    x(new Object[0]);
  }
}

Transparent Desktop Trick

Take a photo of what's behind your computer screen, and set it as your desktop wallpaper. With little care, the results are amazing. See it here.

Labels

So, Blogger got out of beta, and finally it added a labelling feature, which is something I wished for for quite a long time. I decided to label my post to sort them into categories. The categories are (in decreasing order of number of posts at the moment):

software for anything related to software development in general. Java, Open Source, concurrency, programming languages theory. Stuff you'd want to read if you're a fellow software developer.
side interests for serious stuff that I'm interested in as an amateur. Quantum mechanics, astronomy, math, society, politics etc.
mac is for stuff you don't care to read if you aren't interested in Apple computers.
personal is for writings of personal nature.
fun is for art/entertainment/humour things I came across and want to share them with you.
blog a very low volume, blog-related announcements (like this post).

I tried to keep the number of categories to a reasonable minimum, trying to partition the content into as few of them as possible, taking into account possible reasons people read the blog (i.e. it's different for those who track what I do in the software industry, and again different for friends and family).

The links above have associated RSS feeds, so you can choose to syndicate in your reader only those categories you care about. This will probably cause less frustration for me in the future as well, as sometimes I was reluctant to post a more personal writing because I didn't want to decrease the signal-to-noise ratio for (I presume) majority of people who only care for my software-related posts. Heck, I might even post some personal writings in Hungarian now :-)

MacHeist

Via Lifehacker:

MacHeist Bundle is a bundle of 10^* highly popular Mac shareware applications. This week only (which means for the next 2 days and 18 hours now), you can purchase them in a bundle for $49 instead of their combined list price of 308$.

Additionaly, 25% of your purchase goes to charity.

What are you waiting for?

^*To be completely honest, it's 9 apps at the moment. 10th app is TextMate, and it'll get unlocked (meaning a license code will be sent to everyone who purchased the bundle) if the total raised for charity reaches $100k. It's currently at $67k, so there's realistic chance to get TextMate too as part of the bundle.

AAC is better than MP3, Walkman instead of iPod, and what Think Different means to me

Fun fact I learned today: AAC encoding sounds better than MP3 at the same bitrate. Seen here. Re-ripping my CDs right now.

I also bought myself a new cellphone, a Sony Ericsson W850i, and despite some concerns I had initially, the gadget is just brilliant. It has a very decent digital music player built-in (Sony markets them under its Walkman brand) and comes with a 1GB memory stick (I can plug in a bigger one, up to 4GB, and am actively considering buying one), and I can just throw music files from my iTunes library to it using Mac OS X built-in Bluetooth File Exchange app, and it'll nicely index them and add them to its own library. Plays both MP3 and AAC, and recognizes Apple's proprietary iTunes metadata. Just sweet. Guess I'll defer buying myself an iPod for now. Kriszti and me are going on a longish trip to Graz for New Year, so we'll see how it holds up against prolonged use, battery life and overall experience-wise. The phone's contact list and calendar are also syncable with Mac's Address Book and iCal using iSync (after buying a plugin online for 1.43 GBP), a critical feature for me.

As a matter of fact, I initially bought a Samsung Z560, since it's the only phone on the continent at the moment offering HSDPA (think GPRS, only at 1.5MB/s!), but had to return it to T-Mobile after an hour of use and a short frantic search on discussions.apple.com after I realized that it can't sync with Mac, and is not likely it ever will. (Why? Because apparently Samsung has several divisions producing cellphones, 
and each of them uses a different sync protocol, and all of them are proprietary...)

And this brings me to the point of that I'm slowly learning what the Apple slogan "Think Different" might mean to me. It means "shake off your Windows-user assumption that any periferial device will work with your computer". I bought a laser printer earlier this year that only works with Mac after installing some cross-compiled Linux drivers. I bought a cellphone that doesn't sync with Mac (fortunately could exchange it for another). I've learned the lesson. I'm shopping for a joystick now, but am not even looking at anything that doesn't feature "Mac compatible" on the box. There's simply no such thing as "maybe it'll work". It's either "it is supported and then Just Works(tm)", or it is "don't even try". In very rare circumstances you can find stuff that is not supported, but works with more or less effort, but it is really a question of dumb luck. Like Sony Ericsson W850i (with a 3rd party plugin - although to be perfectly honest, Apple supports all Sony Ericsson phones, W850i is just too new, and next release of iSync will probably support it out of box), or my Xerox laser printer (works if you dare install a cross-compiled inux CUPS driver). Think Different = Don't Assume It'll Work. Get Used To Doing More Research Than When You Used Windows.

Dungeon Master miscellanea

My 16-17 year old self has spent more time playing Chaos Strikes Back on Atari ST than my 32-year old self dares to admit.

Turns out, there's a whole fan subculture for Dungeon Master and Chaos Strikes Back out there. There's The Dungeon Master & Chaos Strikes Back Encyclopaedia with information about games as well as a download section with several reincarnations of the games.

Most notable among them is one by one Paul R. Stevens who created an exact replication of the game. Here's how he did it, in his own words found here:

Finally, after many years, I got my hands on the binary executable for the game. I wrote a disassembler to turn it into human-readable op-codes and proceeded to translate it to C++ using the Microsoft Version 6.0 C++ compiler. Eight hours a day for six months. About 120,000 lines of pseudo-assembly language. Crazy thing to do. But it works.

Just insane. Clearly, one of the highest examples of computer nerdiness I've ever came across. Hat off. The biggest achievement is that the resulting code is fairly cross-platform; there are distributions for Windows, Linux, and Mac OS X. And I can certify, the gameplay feeling is identical to that you get from playing it on an original Atari ST. Well, except it loads much faster. And the pixels look blockier on these damned modern high-res displays than they did on a TV screen back in the day. And the Mac OS X port for some reason doesn't deal well with keymaps, so you lose the ability to strafe from the keyboard, which can make the game tedious at times. The Windows version fares better in this regard, and you can even assign mouse clicks on a particular screen coordinate to keys on the keyboard. As anyone who played these games in original will attest, this is an invaluable feature to have as it is much faster to hit 6,4,4,spacebar than to click on four icons on the screen to cast a fireball :-)

Then there's Dungeon Master Java by Alan Berfield, an also cross-platform version of Dungeon Master engine written in Java, with custom raytraced art, giving the game a bit more polished feel.

And then if you look a bit more around on the net with a search engine, you can also find an incredible ammount of custom-designed dungeons fans are creating.

Jeez, now if only I again had as much time as I had 16 years ago...

Poor Man's Message Prioritization

Imagine that you have a distributed enterprise system held together with messaging middleware (JMS, to be specific). Imagine that it's processing a steady load of work in bulk, but not too often there is some time sensitive operation and your system needs to expedite a message or two to meet its time constraints.

If you're lucky, your chosen JMS provider supports message prioritization. Turns out that unfortunately many do not - they simply ignore the priority parameter in MessageProducer.send(). The one I happen to be using also does not support prioritization. Switching to a different provider turned out not to be an option unfortunately - after spending a nontrivial ammount of time (about a month) testing few other, both open source and commercial offerings, none had both the performance and high-availability of the one we originally used.

What I did to overcome the lack of prioritization was "inventing" (quote marks as quite possibly other people had the same idea already) what I'm referring to as "poor man's message prioritization" - instead of using a queue FOO, I now use two queues FOO and FOO_H (for "H"igh priority) and split the JMS sessions used to process the FOO queue into two separate sets of dedicated processors for FOO and FOO_H, typically with only few sessions servicing the "_H" queue, i.e. a 95%/5% split.

What's important to realize is that what's implemented here ain't a message prioritization. It's just separation of traffic. Logically, the queues FOO and FOO_H are treated from the system's point of view as a single queue, and I refer to the individual "physical" queues as "lanes". Sometimes I refer to this technique as "laned JMS".

It does however create the illusion of prioritization as long as the ratio of prioritized traffic to nonprioritized traffic is lower than the ratio of threads processing prioritized traffic to threads processing nonprioritized traffic. It's a workaround for an annoying lack of a feature in the JMS provider. I won't pretend I'm happy with this - it works, and the implementation I came up turned out to be quite clean, but it's still more work to do for me and more complexity in my code; it should've been taken off my back by the JMS provider vendor.

As for technical implementation, it might sound tedious to implement this across the whole codebase, but is actually not that awful:

• On the message producing side, it's sufficient to write a wrapper implementation of JMS Connection interface that is mostly pass-through, except it creates wrapper Sessions, that are themselves mostly pass-through, except they create wrapper MessageProducers, that are again mostly pass-through, but implement the send method with a priority parameter so that if priority is less than 6, the message goes to the base queue, otherwise to the "_H" queue. This way, client code that sends messages just keeps using the Connection.createSession(), Session.createProducer(), and MessageProducer.send() API with priority parameters and is just blissfully unaware of laning in the background.


• On the message consuming side, it'd be tricky to implement this across the board, but luckily all my JMS based message consumer services build on a common codebase that I modelled after the Servlet container/Servlet API model - basically, I have a "JmsServiceContainer" (analogous to Servlet container) that deals with session management and other JMS plumbing, and a "JmsService" interface (analogous to the Servlet interface) whose implementations are more-or-less factories for session-specific MessageListeners that do the actual work on a single message. So, I only had to write the enabling code for laned processing in the "JmsServiceContainer" - basically assign the same JmsService to both lanes of a queue. This way, the "JmsService" implementations also remain blissfully unaware - they're just creating message listeners, and don't care that the messages for those listeners now come from two different queues.

Business trip DTD

<!ELEMENT business-trip (
    airport,
    (office,drink?,dinner,drink+,shower,sleep,breakfast?)+,
    airport
)>

There were efforts to somehow fit a new element, sightseeing into a revised specification, and specify it in the business-trip's content with an optional quantifier, however usability research has shown that real-world documents would almost never contain an instance of it, mainly due to external forces that work to keep the document size at minimum.

Broken LEGO (myth)

My wife found a broken LEGO brick in our son's room this morning. My kids apparently managed to break a LEGO brick in half, and with it the associated myth (well, at least a belief I held) that the damned things are in fact unbreakable in a domestic environment.

Absolutely coincidentally, several hours later today, Slashdot's cover page is graced with an entry "How They Make LEGO Bricks" that actually links to a BusinesWeek article "The making of a... LEGO".

(Very Useless Fact of the Day: I keep my laptop (when it sits on my desk connected to an external display, keyboard, and mouse) sitting on 4 LEGO Duplo bricks I stole from kids to provide better airflow to it.)

Rhino relicensed under MPL/GPL

Mozilla Foundation decided to relicense the Rhino JavaScript interpreter to use the MPL/GPL dual-licensing instead of NPL/GPL dual licensing. The reason is primarily that Apache Software Foundation published a 3rd-party licensing policy recently, and NPL was listed as "Excluded Licenses" in it, therefore prohibiting several Apache projects (Coccon, Batik) to redistribute Rhino in the future. MPL, on the other hand falls into Apache's "Binary Licenses Only" group, which'll allow those projects to bundle Rhino binaries with their distributions. Also, Mozilla's lawyers concluded that Mozilla has the legal power to change the licensing from NPL/GPL to MPL/GPL easily, so it looks like the best solution for the time being.

I plan to release the latest stable branch as Rhino 1.6R5 soon. The binaries will be completely identical to 1.6R4, the only difference being that they'll be recompiled from relicensed source, thus the line number tables in classfiles will reflect the difference in length of the boilerplate license code on top of each source file. Apache folks can then include Rhino 1.6R5 instead of Rhino 1.6R4 binaries in their project distributions, or if they're impatient they can compile it themselves from the "Rhino1_6R3_PATCH" branch in the CVS. (Of course, CVS HEAD is now MPL as well.)

1 << 5

Today's the day when my life duration has doubled for the fifth time, relative to the last such event, (counting my first birthday as the 0th). (With bit of a luck, I'm in for yet another such event down the road.)

For those less math nerd folks out there: I turned 32 today.

I don't usually care too much about arbitrary milestones in the flow of time, my own birthday not really being an exception, yet last night I couldn't help thinking about it (not being able to fall asleep for about two hours after going to bed - I turned from good sleeper to quite erratic sleeper lately). When trying to assess what happened since the last birthday, it always seems life only brings gradual changes (the previous year carries a rather big exception, hopefully I'll be able to write about it sometime soon). However, on such a round number occasion (both %100000 and 0x20), it made me wonder about everything that happened or changed since I was half this age.

And I have to say, it's a hell of a lots of things. My 16-year old self was a quite blissfully unaware gymnasium student in Croatia whose biggest problem was how to skip history classes to go hack on the Apple-II machines in the school computer lab, as well as to write games and fractal generators for Commodore 64 or later for Atari ST. And girls. Were a problem too, that is.

Shortly thereafter, I endured one war and one exodus that completely uprooted me and my family, had to settle in a new country. A bit later found true love, then attended university, and over the passing years grew into several different roles, including that of a husband (for more than eight years now), of a father (for more than seven years now when my son Ákos was born, redoubled the role two years later with Zsuzsi), and of a (well, what at least feels like) reasonably respected IT industry professional. I'd really like to elaborate a bit on all of this here and now, but there are two big driving forces against it: (a) not wanting to bore you to death, and (b) the aforementioned three roles unfortunately don't leave me with much time at present to write sentimental weblog entries about myself.

All in all, the previous 16 years were probably the most dynamic period of my life, past and future. Regardless, I'm looking forward to the next 32 years; stay tuned for the "1 << 6"

Java Notes

When searching few days ago, Google accidentally turned up Java Notes, created by one Fred Swartz (who apparently teaches at University of Maryland Unversity College). Poked around it a bit, and I must say I was pretty impressed by the quality of those examples I looked at; it indeed looks like a nice teaching material for beginning Java programmers, one Mr. Swartz put into many hours to assemble. I mean, just look at the exhaustive discussion of the algorithm for finding the maximum element of an array!

What's an especially nice additional touch is that the author indeed donated all of this to public:

Many textbooks show useful code examples, but ironically copyright them so you can't legally use them! All Java code examples in Java Notes and Java Basics are placed in the public domain.

Of empty bags, or how to coerce a null

Let's say you implement a language (we'll call it "higher layer") atop of an existing language (we'll call it "lower layer"). Examples I work on are Rhino (JavaScript atop of Java) and FreeMarker (text generator template language atop of Java). Imagine that you wish to expose the lower layer objects within the higher layer. What do you do? Well, you implement a wrapper. Your wrapper object will then do its best to disguise the wrapped object as being native to the higher layer (you can use the terms "marshal" or "coerce" instead of "wrap" if you want to appear more serious when talking about it).

Now, this'd be okay if it weren't for the fact that sooner or later there'll inevitably be a situation where there's a semantic ambiguity between the languages, where you can design certain behaviour in more than one way. And inevitably, whichever way it is designed, you'll have users that'd prefer it be designed some other way.

One of such issues is how to coerce a lower layer representation of a null (or nil, or nothing, etc.). Suprisingly, coercing a null the right way is not actually ambiguous at all, yet folks from time to time request it to be done differently, or outright declare the current behaviour to be a bug.

Freshest example is here. Basically, this user would like it if in Rhino, the JavaScript == operator would find equal a null and a wrapper that wraps null. Basically, if x implements the Wrapper interface and ((Wrapper)x).unwrap() == null, he'd like it if ScriptRuntime.eq(x, null) == true.

Now, this'd be utterly problematic. This reminds me of one of my first set theory classes where the teacher stressed that an empty set is not equal to a single-element set containing the empty set (if it was, it would make it impossible to construct the set of natural numbers axiomatically starting from set theory, but I digress). An empty bag is not equal to a bag containing an empty bag, and null is not equal to a wrapper disguising null. (However, any two wrappers that both wrap a null could be equal if the higher-layer language considers null == null to be true for its own null representation, provided it has one at all.)

Although you'd probably be better off if when your custom wrapping code is faced with the request to wrap a lower-layer null, it'd just return a representation of the higher-layer null (if there is one - in Rhino at least JS null is represented by Java null, so custom wrappers can have it quite easily) instead of creating a wrapper object for it. That's the most acceptable way to coerce a null.