Rob and I just wrote this
tools/AutoScaling-1.0.49.1/bin/as-describe-launch-configs $SECURITY --max-records 100 | grep launch-all-staging | cut -d ' ' -f3 | sort -r | tail -n +6 | xargs -I BC tools/AutoScaling-1.0.49.1/bin/as-delete-launch-config $SECURITY --force --launch-config BC
And now we only have six launch configurations in AWS whose names start with "launch-all-staging". It's only a shame that the command line is too long to tweet.
Thursday, 23 February 2012
Thursday, 26 January 2012
Object-oriented programming in Javascript without classes
Like a lot of people, I've been programming with objects a long time. Far too long in Java, and before that in Smalltalk, C++, and even CLOS. In all those languages, objects start with classes. Javascript's different though. There are actually two object-oriented programming models you can adopt: one's a traditional class-based language, whereas the other uses closures instead and lets Javascript's functional nature shine through.
Javascript Classes
The first of these programming models looks a lot like other object-oriented programming languages. Define a class, add a few methods, new up a few instances and poke them;
So far, so good. Let's not worry about whether this is a good way to deal with money or even whether it constitutes good object-oriented design. Instead, let's look at what this tells us about Javascript the object-oriented language. There are some things that might look like problems if you're used to "proper" (Java) classes. All the variables are public, come to that so are all the methods. There's also a certain amount of clutter - what's with the mysterious "prototype"? And there's some weird stuff going on with "this". Try this method:
This won't work as it stands. The keyword "this" refers to the instance of Account that we're working with inside a method of Account, but NOT inside a nested function. So in this example, "this" refers to the anonymous function that's mapped across the array. To get this to work I need this magic incantation:
To put it another way, this this isn't the same as that this. We Node JS programmers live in a world where every other line involves a nested function for NodeJS to call back, so we see a lot of this.
And now imagine that I want to make handleDebit private so that only handleSeveralDebits is public. There's no way to achieve this while handleDebit is still attached to the prototype. There are lots more hoops you can jump through (Douglas Crockford has several) but these just add to the clutter.
Javascript objects without classes
To recap: Javascript classes gave us public instance variables, the prototype special variable, "self=this", no private methods... Fortunately, Javascript is a functional language with closures as well. How about this implementation:
A simple function that returns an object. There's no class here, but that's ok, because in Javascript an object is whatever I say it is. Objects made like this will behave just like instances of the Account class, except that we won't be able to get at their instance variables or the private handleDebit method. We aren't using the "new" keyword, nor the "prototype", and best of all, not even the dreaded "this". There's simply less stuff to read. And there's less stuff to comprehend: just try googling "understanding the keywords prototype and constructor in JavaScript".
An alternative that some like is this:
Much the same, but the public api is a bit easier to scan.
Caveat emptor
It's not all good news though. These styles uses a lot more memory, because each instance has its own copy of each function. In Node 0.5.9, at least, this is the difference between (very roughly) 40 and 275 bytes per Account object. Which may or may not matter to your real application.
Conclusion
Javascript doesn't need classes. It's instructive that classes need some reserved keywords whose behaviour is easy to misunderstand, whereas the classless closure only needs the basic syntax of the language. I think this hints that programming with classes is an uneasy bolt-on intended to make the language approachable for Java exiles, whereas the pure core Javascript wants us to use classless objects with a pure functional syntax.
In this article we haven't talked about inheritance. My general attitude is that inheritance is a not particularly important special case of delegation, but that sounds like a topic for another day.Tuesday, 6 October 2009
Toumani Diabate and Wanlov the Kubulor
Clearly I'm not inspired to write about software at the moment, so instead, I think I'll use this blog to supplement my increasingly creaky memory and record my thoughts on things I see.
I just got back from holiday in South Africa (fantastic, thanks for asking) but while there I saw Toumani Diabate and Wanlov the Kubulor perform as part of a Cape Town "musical intervention" called, rather splendidly, the Pan-African Space Station.
Toumani D. is a relatively familiar name, but first, the support... Wanlov come from Ghana and comprise vocals, balafon, shekere, djembe, one string bass, some sort of lute, trumpet, box drum and various other bits of percussion. All this plus quirky lyrics ranging from jokey love song through full on political stuff, and a rather magnetic lead singer. I really enjoyed this gig, lots of fun. The CD isn't quite as good as the live band, it has a rather westernised or manufactured feel compared to the loose and swinging live band. 8/10 for the gig.
Toumani Diabate plays solo on the Kora (a 21 string African harp). He gave us a quick explanation of the instrument: you have two thumbs to play the bass, one index finger to play the melody, and the other index finger to "improvise". He's a spell-binding master. Most of his songs last ten minutes and it often feels like that isn't long enough. It puts you in mind of someone like Sonny Rollins playing solos: he establishes a theme and then plays endless variations on it, drifting away before returning, but never losing the structure. 10/10: I'd watch him f ive times a week if he played in my street.
A word about the venue: the Slave Church Museum in Cape Town was at full capacity of a few hundred, the acoustics were excellent, and this may have swelled the scores I've given both acts.
I just got back from holiday in South Africa (fantastic, thanks for asking) but while there I saw Toumani Diabate and Wanlov the Kubulor perform as part of a Cape Town "musical intervention" called, rather splendidly, the Pan-African Space Station.
Toumani D. is a relatively familiar name, but first, the support... Wanlov come from Ghana and comprise vocals, balafon, shekere, djembe, one string bass, some sort of lute, trumpet, box drum and various other bits of percussion. All this plus quirky lyrics ranging from jokey love song through full on political stuff, and a rather magnetic lead singer. I really enjoyed this gig, lots of fun. The CD isn't quite as good as the live band, it has a rather westernised or manufactured feel compared to the loose and swinging live band. 8/10 for the gig.
Toumani Diabate plays solo on the Kora (a 21 string African harp). He gave us a quick explanation of the instrument: you have two thumbs to play the bass, one index finger to play the melody, and the other index finger to "improvise". He's a spell-binding master. Most of his songs last ten minutes and it often feels like that isn't long enough. It puts you in mind of someone like Sonny Rollins playing solos: he establishes a theme and then plays endless variations on it, drifting away before returning, but never losing the structure. 10/10: I'd watch him f ive times a week if he played in my street.
A word about the venue: the Slave Church Museum in Cape Town was at full capacity of a few hundred, the acoustics were excellent, and this may have swelled the scores I've given both acts.
Thursday, 16 April 2009
Theories in jUnit revisited
A minor update on this stuff (see earlier post).
I've just got back from SPA2009, where there was a lot of excitement about Haskell. This seems interesting to me too, as I'm old enough to have Lisp and Prolog on the CV. One of the things I got to play with in one session was "quickcheck", a testing tool for Haskell.
Because Haskell is purely functional (for the most part), it lends itself to unit testing. Just call a function with some arguments, make some assertions about the result, no side-effects are even possible so you're done. Quickcheck allows you to constrain the process for generating sets of arguments and then you just let the system rip. So you can have, for example, one test that generates valid sets of arguments that checks for a correct result, and another that generates invalid sets that checks for appropriate errors. Much like theories in jUnit, but with the addition of automatic generation of sets of test parameters.
However, it seems clear that the Haskellites amongst us use this tool in an exploratory fashion. Hunting down that tricky to find bug that pops up now and then on live code? Not quite sure what the library in front of you does? Want to stress-test a piece of code that's going to have to cope with noisy data? For actual unit (regression) testing of real code, it's much less useful, not least because there's some randomness in the arguments which makes regression problematic.
So there it is: quickcheck for poking around, and HUnit (it had to exist) for your unit tests.
I've just got back from SPA2009, where there was a lot of excitement about Haskell. This seems interesting to me too, as I'm old enough to have Lisp and Prolog on the CV. One of the things I got to play with in one session was "quickcheck", a testing tool for Haskell.
Because Haskell is purely functional (for the most part), it lends itself to unit testing. Just call a function with some arguments, make some assertions about the result, no side-effects are even possible so you're done. Quickcheck allows you to constrain the process for generating sets of arguments and then you just let the system rip. So you can have, for example, one test that generates valid sets of arguments that checks for a correct result, and another that generates invalid sets that checks for appropriate errors. Much like theories in jUnit, but with the addition of automatic generation of sets of test parameters.
However, it seems clear that the Haskellites amongst us use this tool in an exploratory fashion. Hunting down that tricky to find bug that pops up now and then on live code? Not quite sure what the library in front of you does? Want to stress-test a piece of code that's going to have to cope with noisy data? For actual unit (regression) testing of real code, it's much less useful, not least because there's some randomness in the arguments which makes regression problematic.
So there it is: quickcheck for poking around, and HUnit (it had to exist) for your unit tests.
Wednesday, 4 February 2009
Theories in jUnit 4
Part of what's new in jUnit4 is theory functionality. The notion here is that you write your unit test as a series of methods, each of which states the assumptions under which it applies, and then asserts something about the outcome of the test. Substituting the words precondition and postcondition for assumption and assertion gives me a reassuring sense of deja vu.
This article is about my attempts to write a little theory, and how I got stuck. If anyone out there that can help me understand this better, I would be very grateful!
An example
SUN Spots use IEEE 802.15.4 radio communications. This standard uses 64-bit addresses. People usually like to see these addresses as four quartets of hex numbers (e.g. "0041.1DAF.078E.0042"), but the internals of the Java comms stack would rather see them as 64-bit numbers. And in a few places, they appear as strings containing the decimal value of the address.
In the code there's a class called IEEEAddress, which, startlingly enough, represents one of these addresses and takes care of the conversions. The code inside this class for determining the long from a String looks something like this
There are a couple of helper methods here: containsOnlyDecimalDigits(aString) and isFourQuartetsOfHexDigitsSeparatedByFullStops(aString). These are moderately complex, but we shouldn't need to look at them to understand what follows.
The existing tests throws a load of test cases at the code, each of which looks somewhat like this:
So far, so good. So next, I tried to write the tests as a theory instead. Here's my first try at that:
The idea of a theory is that each data point is thrown at each theory method in turn. Thus in my case, we'll get nine test executions. In cases where the result of "assumeTrue(...)" returns false, the test will be abandoned, but will be ignored (that's not a failure, the data point just doesn't apply to that clause of the theory). Where the assumption passes, the rest of the method executes like a normal jUnit test.
Now, I can write a few extra data points, and this thing will exercise the code as effectively as the existing unit test. It even works, runs all the cases and it's kind of neat. However, and here's my issue with all this, the theory basically replicates the code under test - and so it's hardly surprising that it passes!
My first thought was to write the code differently between the tests and the implementation. A bit of poking around reveals that I could probably download macrest-text-patterns, express the notion of all digits and/or the dotted hex notation as regular expressions, and use that. But then, if I thought that was the way to do the parsing, I could do much the same inside my live code too. And once again, what exactly am I testing? Or am I supposed to implement the code twice, once optimally, and once using a poorer algorithm that I invent for testing?
Then I read http://shareandenjoy.saff.net/tdd-specifications.pdf (an interesting paper about theories). This paper suggests that it might be better to write theories as identities based on some sort of round trip. Here's a fragment of an alternative theory based on that idea:
This should be true for absolutely all cases where the assumption holds, and it doesn't know anything about how to do the conversions between strings and longs, which is a step forward. But...
1. It is vulnerable to a pair of matching errors in the code. For example, imagine a bug where IEEEAddress.asLong() yields a result with the wrong sign. If IEEEAddress.asDottedHex() also reversed the sign, the theory would pass. For this reason, such a theory would need to be coupled with a couple of the more traditional tests.
2. More significantly, though, the complexity in the class under test is inside the helper methods isFourQuartetsOfHexDigitsSeparatedByFullStops(aString) and containsOnlyDecimalDigits(aString), and the theory still shares those with the code under test.
I'm not sure what to do next with this. Maybe theories just aren't good with code where the values of parameters are highly constrained. Or maybe I'm missing some obvious next step. Any ideas?
This article is about my attempts to write a little theory, and how I got stuck. If anyone out there that can help me understand this better, I would be very grateful!
An example
SUN Spots use IEEE 802.15.4 radio communications. This standard uses 64-bit addresses. People usually like to see these addresses as four quartets of hex numbers (e.g. "0041.1DAF.078E.0042"), but the internals of the Java comms stack would rather see them as 64-bit numbers. And in a few places, they appear as strings containing the decimal value of the address.
In the code there's a class called IEEEAddress, which, startlingly enough, represents one of these addresses and takes care of the conversions. The code inside this class for determining the long from a String looks something like this
...
if (containsOnlyDecimalDigits(aString)) {
return Long.parseInt(entry, 10);
} else if (isFourQuartetsOfHexDigitsSeparatedByFullStops(aString)) {
return Long.parseInt(aString.replace(".", ""), 16);
} else {
throw new IllegalArgumentException(aString + " isn't a valid IEEE address");
}
...
There are a couple of helper methods here: containsOnlyDecimalDigits(aString) and isFourQuartetsOfHexDigitsSeparatedByFullStops(aString). These are moderately complex, but we shouldn't need to look at them to understand what follows.
The existing tests throws a load of test cases at the code, each of which looks somewhat like this:
...
IEEEAddress address = new IEEEAddress("0123.4567.89ab.cdef");
assertEquals("Long should be parsed correctly", 0x123456789ABCDEFL, address.asLong());
...
So far, so good. So next, I tried to write the tests as a theory instead. Here's my first try at that:
@RunWith(Theories.class)
public class IEEEAddressTheory {
@DataPoint public static String dp1 = "0123.4567.89ab.cdef";
@DataPoint public static String dp2 = "0123456789";
@DataPoint public static String dp3 = "0123.456789.23"; // invalid example to test exceptions
@Theory public void dottedStringsContainHexDigits(String aString) {
assumeTrue(isFourQuartetsOfHexDigitsSeparatedByFullStops(aString));
String withoutDots = aString.replace(".", "");
long expectedResult = Long.parseLong(withoutDots, 16);
assertEquals(expectedResult, new IEEEAddress(aString).asLong());
}
@Theory public void undottedStringsContainDecimalDigits(String aString) {
assumeTrue(containsOnlyDecimalDigits(aString));
long expectedResult = Long.parseLong(aString, 10);
assertEquals(expectedResult, new IEEEAddress(aString).asLong());
}
@Theory public void invalidStringsThrowIllegalArgumentException(String aString) {
assumeTrue(
!isFourQuartetsOfHexDigitsSeparatedByFullStops(aString) &&
!containsOnlyDecimalDigits(aString));
try {
new IEEEAddress(aString).asLong();
fail("Should get exception for bad syntax");
} catch (IllegalArgumentException e) {};
}
}
The idea of a theory is that each data point is thrown at each theory method in turn. Thus in my case, we'll get nine test executions. In cases where the result of "assumeTrue(...)" returns false, the test will be abandoned, but will be ignored (that's not a failure, the data point just doesn't apply to that clause of the theory). Where the assumption passes, the rest of the method executes like a normal jUnit test.
Now, I can write a few extra data points, and this thing will exercise the code as effectively as the existing unit test. It even works, runs all the cases and it's kind of neat. However, and here's my issue with all this, the theory basically replicates the code under test - and so it's hardly surprising that it passes!
My first thought was to write the code differently between the tests and the implementation. A bit of poking around reveals that I could probably download macrest-text-patterns, express the notion of all digits and/or the dotted hex notation as regular expressions, and use that. But then, if I thought that was the way to do the parsing, I could do much the same inside my live code too. And once again, what exactly am I testing? Or am I supposed to implement the code twice, once optimally, and once using a poorer algorithm that I invent for testing?
Then I read http://shareandenjoy.saff.net/tdd-specifications.pdf (an interesting paper about theories). This paper suggests that it might be better to write theories as identities based on some sort of round trip. Here's a fragment of an alternative theory based on that idea:
...
@Theory public void roundTripsWorkForDottedHex(String aDottedHexString) {
assumeTrue(isFourQuartetsOfHexDigitsSeparatedByFullStops(aDottedHexString));
long numberValue = new IEEEAddress(aDottedHexString).asLong();
assertEquals(aDottedHexString, new IEEEAddress(numberValue).asDottedHex());
}
...
This should be true for absolutely all cases where the assumption holds, and it doesn't know anything about how to do the conversions between strings and longs, which is a step forward. But...
1. It is vulnerable to a pair of matching errors in the code. For example, imagine a bug where IEEEAddress.asLong() yields a result with the wrong sign. If IEEEAddress.asDottedHex() also reversed the sign, the theory would pass. For this reason, such a theory would need to be coupled with a couple of the more traditional tests.
2. More significantly, though, the complexity in the class under test is inside the helper methods isFourQuartetsOfHexDigitsSeparatedByFullStops(aString) and containsOnlyDecimalDigits(aString), and the theory still shares those with the code under test.
I'm not sure what to do next with this. Maybe theories just aren't good with code where the values of parameters are highly constrained. Or maybe I'm missing some obvious next step. Any ideas?
Sunday, 4 January 2009
Ten thousand hours...
A friend of mine is a sports physiotherapist. He's pretty good at this and has worked with premiership footballers, Belgian international Squash players and others. Apparently it's common knowledge in his world that all top sportspeople put in around 10,000 hours practice before they reach the top. That's about 20 hours a week for 10 years. He emphasises that this was practising as distinct from playing the sport. One key difference is the continuous involvement of a coach to make you do it right.
What does this mean for programmers? I think that pair programmers have a coach present, and so they're building their 10,000 hours. On this basis, 10,000 hours of pair programming makes you an international. No amount of lone programming gets you there though - you're just programming.
What does this mean for programmers? I think that pair programmers have a coach present, and so they're building their 10,000 hours. On this basis, 10,000 hours of pair programming makes you an international. No amount of lone programming gets you there though - you're just programming.
There's no comparison
XP Day 2008. XP Day isn't really about XP any more - it's about whatever the people that go every year are currently obsessed with. On this occasion, that seemed to be two topics. One was that old favourite, how shall we know good code when we see it? Not much to say about that except that I was pleased to find lots of other people in the middle of Bob Martin's "Clean Code", which is focused thereabouts.
The other obsession was lean thinking. This is one of those myriad attempts to improve software practice by copying something that worked somewhere else. In this case, Toyota came up with a bunch of practices that helped them to make cars more cheaply in the immediate post-war era. I mentioned this over the weekend to a friend whose job consists of trying to make various car factories run more efficiently. As you might expect, he knows a lot about value streams, kanbans, and the rest of this stuff, and he immediately came back with "but what has all that got to do with software?".
I was reminded of an OOPSLA in the late nineties. At that time, pattern languages were all the vogue, and Chris Alexander - the architect who invented pattern languages to capture architectural knowledge - had been invited to give the keynote. He shambled on stage, and expressed himself vaguely bemused to be there. Why would you all be interested in something designed for use with architecture? he asked us.
It seems to me that we do this a lot in software. Apart from lean thinking and architecture, other past efforts have included the SEI models (one of many other attempts to compare software with manufacturing), making movies, mountaineering, oil exploration, collaborative game playing, building buildings, and plenty more besides.
These can be sources of entertainment. I've spent some happy hours annoying movie-making friends by trying to make comparisons. But mostly, I don't think these analogies help much with the goal of getting better at writing software.
Years ago I saw Bertrand Meyer give a talk in which he said that the significance of a piece of advice was inversely linked to the plausibility of the opposite. If someone advises you to choose readable variable names, that's not advice: you were unlikely to make an effort to choose unreadable names. On the other hand, if you're advised to "choose names that express what is to be done rather than how" then you have real advice, because it's not immediately obvious that "how" is the wrong answer.
Much of the advice that comes from these analogies seems to me to fail the Meyer test. I was initially taken by someone talking at XP Day about applying the principles of lean applied to software. One outcome was the notion of not having any more than a small number of tasks on the go at once. But then I took a step back to consider the alternative. Deliberately strive to do lots of things at once? Was I about to do that? About the best you can say is that this changes the emphasis, but then you have to wonder, away from what?
Other debates about the management process had this same unsatisfactory feel. Reminders of lots of common sense stuff, but nothing that might change your practice. Breakthroughs in software development - the move from waterfall to iterative, for example - I don't think come from analogies. All the "good stuff" for me at XP Day happened where the topic under discussion was software development, in and of itself. I sat for an hour in an open space discussion about what makes software programs easy to read. I came away with some genuinely useful insights that will make me do something different in future. From here on in, I think I'm going to try and get better at software by doing and talking about software.
The other obsession was lean thinking. This is one of those myriad attempts to improve software practice by copying something that worked somewhere else. In this case, Toyota came up with a bunch of practices that helped them to make cars more cheaply in the immediate post-war era. I mentioned this over the weekend to a friend whose job consists of trying to make various car factories run more efficiently. As you might expect, he knows a lot about value streams, kanbans, and the rest of this stuff, and he immediately came back with "but what has all that got to do with software?".
I was reminded of an OOPSLA in the late nineties. At that time, pattern languages were all the vogue, and Chris Alexander - the architect who invented pattern languages to capture architectural knowledge - had been invited to give the keynote. He shambled on stage, and expressed himself vaguely bemused to be there. Why would you all be interested in something designed for use with architecture? he asked us.
It seems to me that we do this a lot in software. Apart from lean thinking and architecture, other past efforts have included the SEI models (one of many other attempts to compare software with manufacturing), making movies, mountaineering, oil exploration, collaborative game playing, building buildings, and plenty more besides.
These can be sources of entertainment. I've spent some happy hours annoying movie-making friends by trying to make comparisons. But mostly, I don't think these analogies help much with the goal of getting better at writing software.
Years ago I saw Bertrand Meyer give a talk in which he said that the significance of a piece of advice was inversely linked to the plausibility of the opposite. If someone advises you to choose readable variable names, that's not advice: you were unlikely to make an effort to choose unreadable names. On the other hand, if you're advised to "choose names that express what is to be done rather than how" then you have real advice, because it's not immediately obvious that "how" is the wrong answer.
Much of the advice that comes from these analogies seems to me to fail the Meyer test. I was initially taken by someone talking at XP Day about applying the principles of lean applied to software. One outcome was the notion of not having any more than a small number of tasks on the go at once. But then I took a step back to consider the alternative. Deliberately strive to do lots of things at once? Was I about to do that? About the best you can say is that this changes the emphasis, but then you have to wonder, away from what?
Other debates about the management process had this same unsatisfactory feel. Reminders of lots of common sense stuff, but nothing that might change your practice. Breakthroughs in software development - the move from waterfall to iterative, for example - I don't think come from analogies. All the "good stuff" for me at XP Day happened where the topic under discussion was software development, in and of itself. I sat for an hour in an open space discussion about what makes software programs easy to read. I came away with some genuinely useful insights that will make me do something different in future. From here on in, I think I'm going to try and get better at software by doing and talking about software.
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