DBIC Training in Granada

It’s been a while since I’ve run a training course alongside a YAPC. By my calculations, the last time was Riga in 2011. But I’ve been talking to the organisers of this year’s conference and we have plan.

I’m going to be running a one-day introductory course on DBIx::Class before the conference (I think it’ll be on 1st September, but that’s not 100% certain yet). Full details are on the conference web site. There’s an early-bird price of 150 Euro and the full price is 200 Euro. The web site says that the early-bird price finishes today, but I wouldn’t be at all surprised if that gets extended for a few days at least.

Of course, readers of this blog will all already be experts in DBIC and won’t need this course. But I’m sure that most of you will have a colleague who would benefit from… well… a refresher on who DBIC works. Why not see if your company will pay for them to attend the course 🙂

The course size is limited. So you might want to think about booking soon.

Hope to see some of you in Granada.

Two updates:

  1. The date has now been confirmed as 1st September.
  2. The early-bird pricing has been extended until 1st June.

Subroutines and Ampersands

I’ve had this discussion several times recently, so I thought it was worth writing a blog post so that I have somewhere to point people the next time it comes up.

Using ampersands on subroutine calls (&my_sub or &my_sub(...)) is never necessary and can have potentially surprising side-effects. It should, therefore, never be used and should particularly be avoided in examples aimed at beginners.

Using an ampersand when calling a subroutine has three effects.

  1. It disambiguates the code so the the Perl compiler knows for sure that it has come across a subroutine call.
  2. It turns off prototype checking.
  3. If you use the &my_sub form (i.e. without parentheses) then the current value of @_ is passed on to the called subroutine.

Let’s look at these three effects in a little more detail.

Disambiguating the code is obviously a good idea. But adding the ampersand is not the only way to do it. Adding a pair of parentheses to the end of the call (my_sub()) has exactly the same effect. And, as a bonus, it looks the same as subroutine calls do in pretty much every other programming language ever invented. I can’t think of a single reason why anyone would pick &my_sub over my_sub().

I hope we’re agreed that prototypes are unnecessary in most Perl code (perhaps that needs to be another blog post at some point). Of course there are a few good reasons to use them, but most of us won’t be using them most of the time. If you’re using them, then turning off prototype checking seems to be a bad idea. And if you’re not using them, then it doesn’t matter whether they’re checked or not. There’s no good argument here for  using ampersands.

Then we come to the invisible passing of @_ to the called subroutine. I have no idea why anyone ever thought this was a good idea. The perlsub documentation calls it “an efficiency mechanism” but admits that is it one “that new users may wish to avoid”. If you want @_ to be available to the called subroutine then just pass it in explicitly. Your maintenance programmer (and remember, that could be you in six months time) will be grateful and won’t waste hours trying to work out what is going on.

So, no, there is no good reason to use ampersands when calling subroutines. Please don’t use them.

There is, of course, one case where ampersands are still useful when dealing with subroutines – when you are taking a reference to an existing, named subroutine. But that’s the only case that I can think of.

What do you think? Have I missed something?

It’s unfortunate that a lot of the older documentation on CPAN (and, indeed, some popular beginners’ books) still perpetuate this outdated style. It would be great if we could remove it from all example code.

Modern Perl Articles

Back in 2011 I wrote a series of three articles about “Modern Perl” for Linux Format. Although I mentioned all three articles here as they were published, I didn’t post the actual contents of the articles as I wasn’t sure about the copyright situation.

But now I suspect that enough time has passed that copyright is no longer going to be an issue, so I’ve added the full text of the articles to this site. The articles are all about writing a simple web application to track your reading. They use DBIx::Class and Dancer.

Let me know if you find them interesting or useful.

Penetration Testing with Perl

I was sent a review copy of Penetration Testing with Perl by Douglas Berdeaux. I really didn’t like it. Here’s the review I’ve been sharing on Amazon and Goodreads.

I’ve been wanting to learn a bit about Penetration Testing for a while and as Perl is my programming language of choice this seemed like a great book to choose. Unfortunately, it wasn’t.

I have no doubt that the author knows what he is talking about when it comes to Penetration Testing, but there were several things that prevented this book from transferring much of that knowledge to me.

Firstly, the typesetting in the book is terrible. I was reading the Amazon eBook edition – it’s possible that the printed version is better. For example, there’s a lot of code in this book and it’s in a proportional font. In order for code to be readable, it needs to be in a fixed-width font. Also, there are two or three places where an equation appears in the text, but it appears in an unreadably small font. I have just checked in the PDF version of the book and neither of these problems appear there. It would seem that this is down to a problem in Packt’s eBook creation process.

Secondly, it’s obvious that English is not the author’s first language. At times this really prevents him from getting his point across clearly. I’m very happy to see non-native speakers publishing books in English. But the publishers need to provide high quality proof-readers to ensure that the language is good enough.

Thirdly, the organisation of the book is a little haphazard. The first couple of chapters are introductions to Perl and Linux, but after that we are dropped immediately into a discussion of network sniffing. Later in the book there are chapters on intelligence gathering, social engineering and password cracking. These are all far simpler topics which could have served as a gentle introduction to the book, getting people up to speed on Perl before delving into the complex internals of network packets. Once again, I think this should be the responsibility of the publisher. There should be a good editor working on the book alongside the author and shaping the manuscript so that the story it tells guides the user through the subject as easily as possible.

Finally, the book falls short in its technical content. I can’t comment on the author’s explanations of Penetration Testing (I was, after all, reading the book to learn about that topic), but the Perl code that he uses throughout the book is really bad. He is obviously someone who only ever learned enough Perl to get his job done and never bothered to learn how Perl really works or to keep his knowledge up to date. As a result, the book is full of the kind of code that gives Perl its reputation as a write-only language. The idioms that he uses are often out of date (using ‘-w’ instead of ‘use warnings’, for example), confusing (predeclaring subroutines unnecessarily, using ampersands on function calls) or just plain wrong (‘my ($x, $y, $z) = 0 x 3’ just doesn’t do what he thinks it does). Actually, it’s worse than that. It’s not just Perl he doesn’t understand, it’s the fundamentals of good software engineering. His code is a confusing mess of global variables and bad design. This is another failure by the publisher. There should have been a competent technical editor checking this stuff.

I’ve read four or five Packt books now. They’re all of this standard. None of them should have been published. But Packt seem to have hit on a good business model. They find unknown authors and produce books as cheaply as possible. Their publishing process omits all of the editing and checking that more reputable publishers use. The books that come out of this process are, of course, terrible. But, for reasons I can’t understand, people still buy them.

Packt books – just say no.

London Perl Jobs Mailing List

London.pm is undergoing one of its periodic reorganisations. We’re in the process of moving our web site over to a new server and as part of that move, we’ve decided that we’ll move our mailing list infrastructure to a third party system. Both the main discussion list and the announcements list will be run on Sympa.

But that’s not all the lists we currently have. In particular, we had a London Perl Jobs list, which anyone could use to post details of Perl jobs in London. It’s been decided that this list is too much hassle to keep up. Apparently, it needs a pretty high level of work from moderators. So that list isn’t going to be migrated and it will quietly die.

I thought that was a bit of a shame. I think it’s a useful list. And, in particular, I think it would be easy for outsiders to misread the reasons for the closure – given the current discussions about the death of Perl. Perhaps the list was killed off because there are no longer any Perl jobs in London (you and I both know that’s not true, but not everyone is following the situation as closely as we are).

So I decided to do something about it. I just happened to have a useful-looking domain sitting around not doing very much, so I’ve set up a jobs mailing list over there. Feel free to subscribe if you’re interested in Perl jobs in London. And, more importantly, please encourage people who are looking for Perl programmers in London to post their jobs to jobs@londonperl.co.uk.

Currently, the list is configured like this:

  • Archives are public
  • By default, replies go to the poster rather than the list
  • Posts are accepted from anyone
  • All posts are moderated

I’ll be happy to reconsider any of those settings once the list has been running for a while. I’m also considering setting up an associated jobs discussion list, if people think that would be useful.

See you on the mailing list.