some time ago I found an article (Roles: Composable Units of Object Behavior) describing the pros of using Roles versus Interfaces or other ways of dealing with behavior requirements. Does any of you knows where I can find more literature about that, or knows more about Roles?
I know that that's almost a research topic, but maybe someone (maybe some Perl programmer) has tried something with it (Moose?).
Note: the reason for adding tag "perl" is that maybe Perl programmers are more likely to give an answer.
For Moose based examples, you should check this and that example and this specification.
ETA: For the theoretical aspects, see this page
Related
I'm using ScalaJS with Play. Many of the models I'd like to use on both JS and JVM platforms involve dates and times. Given the lack of a cross-platform date/time library, how are people approaching this?
Things I know about:
scalajs-java-time project (https://github.com/scala-js/scala-js-java-time) to port JDK8's java.time api to Scala.js. Unfortunately, it's far from complete and judging by the commit logs, seems to have stalled.
https://github.com/mdedetrich/soda-time is a port of JodaTime to Scala/Scala.js. But it's not ready for production use.
An old post at https://groups.google.com/forum/#!topic/scala-js/6JoJ7x-VxLA suggests storing milliseconds in shared code and then doing implicit conversions on each platform to either js.Date or JodaTime. But we really need a common interface, which this doesn't give.
Li Haoyi's excellent "Hands-on Scala.js" has a simple cross-platform library (http://www.lihaoyi.com/hands-on-scala-js/#ASimpleCross-BuiltLibrary) that could, in theory, be extended to come up with an API in /shared that delegates to JodaTime on the jvm and Momento on js -- but that sounds like a lot of work.
(added later) https://github.com/soc/scala-java-time is based on an implementation of java-time that was contributed to OpenJDK. The README claims that most stuff is working. Right now, this looks like the most promising approach for my needs.
Any advice from those who have gone before me? Right now the fourth options seems like my best bet (with the API limited to stuff I actually use). I'm hoping for something better.
I was in the same boat as you, and the best solution I came up with was cquiroz's scala-java-time library. From reading the comments to your question above, it appears you landed at the same place eventually!
I came here from a google search, and given how much better this solution is than the alternatives you mentions above, let's consider marking this question as resolved for future visitors.
The documentation of scala macro is very hard to understand, so I think it must have some background knowledge if one wants to use it in real case.
And I ask help for what these knowledge are.
c.Expr[Unit](Block(treesWithSeparators.toList, Literal(Constant(()))))
it is a code snippet of macro, and there are little info available for what Block means, and other similar terms. It is hard to go deep in if these key points lost.
So if anyone knows where exists a more detailed documentation or tutorial, please tell me, thanks:)
It is hard to go deep in if these key points lost.
Yes that is true but it is good that not everyone can get a way into macros. They are a powerful feature and users that don't understand them fully should not use them.
Diving into macros requires a lot of self learning, there is no easy way to learn how they work and how to work with them.
Nevertheless there is already a lot of useful documentation out there. For example this question wants to know how to understand the AST: Where can I learn about constructing AST's for Scala macros?
This question on the other side gives some value on how to work with reify: What's the easiest way to use reify (get an AST of) an expression in Scala?
On docs.scala-lang.org there is an excellent overview available that describes what macros can do and what not. The official homepage also contains lots of useful information.
And reading further questions here on StackOverflow, looking at source code on GitHub or searching the web for blog posts on macros shouldn't be that difficult.
For the beginning this should be enough to find a way into macro hell.
I've looked into the source code of DBIx::Class recently and found that I don't understand a thing (though I mastered a couple tricks while trying to).
So my question is: which CPAN modules are a must read for someone who wants to learn, and in what order?
If I were doing the same I’d probably start with the ::Tiny space. I’d expect it to be less distracting—fewer edge cases cluttering things—and more idiomatic—terseness lends itself to Perl idiom—in general.
Then I’d attack the medium–large nodes from this excellent document—Map of the CPAN’s authors (large PDF). Update: Web version. Zoom into the bigger nodes then search on search.cpan.org for them. The largest nodes sometimes represent old-school and while exceptional code exists in the old school, not a lot of good teaching examples do (so I say). Authors like Miyagawa, Kennedy, and Kogman come to mind immediately as worth reviewing. There are plenty of others. Basically any module you see recommended here often, look up the author and poke around his or her other packages, as it were.
I learned quite a bit (tie-ing, platform independent filesystem access, etc) by reading the code for File::chdir. It is also a very handy module to use in your scripts, I use it all the time.
I would also add to bvr's list: read the source for modules that you use frequently, since you are already familiar with their expected behavior, you can more clearly see what is being done to achieve that result.
The question is what you want to learn, but it is certainly good idea to study various modules, because you learn to read other people code and learn various tricks. Some random recommendations I can think of
start with smaller modules with clear interface you know and are interested in
once you feel familiar with organization of modules and basics, try something larger
try rather newer modules
look into test suite and into examples
if you don't understand specific piece, try to make reduced example a play with it
It is hard to recommend something specific, but I liked my recent look into Web::Scraper module.
If you're fluent in perl - if don't perldoc ;) - , sugest learn the packages Task::Kensho or Modern::Perl.
These packages do cover comprehensive in culture Perl, since tests until hacks, passing by crawling, modules to developers, e-mail, dates, modern oriented obejct in Perl.
Participe of discussion lists, read the history of list, irc.
Perl have many tricks, the community always responds with enthusiasm =)
I've been asked to run a workshop and coding dojo soon for people to try out Scala and try to build something with it. The attendees are all going to be new to Scala, and could come from any of a number of languages (I'm presuming they can code in at least one mainstream language - I'm including syntax comparisons with Java, C#, Python and Ruby).
Part of the appeal of Scala is that it's practical - you can use it as a drop-in "power Java" (Java with less syntactical clutter, closures, immutability, FP, traits, singleton objects, nifty XML handling, type inference etc.) that still runs on the JVM (and on the .NET CLR supposedly) and doesn't require you to change build tools, server infrastructure, libraries, IDEs and so on. Most of the katas I've seen have been fun but not 'real world' - mathematical challenges like Project Euler and so on. These don't seem appropriate as we're trying to explore the use of it as a practical, real world language that people could consider using for both hacking and work, and because people aren't necessarily going to be too familiar with either the deeper parts of the Scala syntax or necessarily of the concepts behind functional programming.
So, has anyone come across any more practical, everyday katas rather than arithmetical 'problem solving' ones? Katas, that is, that can test whether the language, libraries and tools can satisfy the use cases of the actual day-to-day programming most people have to do rather than testing out. (Not that the impractical ones aren't fun, but just not appropriate for the kind of thing I've been asked to run.)
If I can't find good examples, I'm thinking that it might be useful to try and build something like a library catalogue - the event is for programmers who primarily work on building infrastructure for universities (and in education and culture - museums, galleries, schools, libraries and so on). It's a bit boring though, but it's the sort of thing that the attendees work on in their day-to-day existence. Any suggestions?
There is a creative commons licensed introductory training course with hands-on exercises here:
http://github.com/javaBin/scala-training-slides
http://github.com/javaBin/scala-training-code
The slides are in Open Office format. If you don't have this installed, you can upload them to SlideShare, which will convert them for online viewing.
Most of the programming examples in my blog are, effectively, coding dojo exercises. Particularly the matrices series, but also the puzzles and 99 beers. Now, don't disregard the matrices series as being "mathematical", because the problems I concern myself in it are related to the construction of classes in Scala, not to doing fancy algorithms. In fact, I pretty much skip over the mathematical algorithms themselves.
Now, 99 Scala Problems and pretty much everything from Project Euler are nice exercises for the functional part of Scala, but I understand that not to be your emphasis. I do recommend retronym's answer. Rosetta Code, not being functionally oriented, might have more general examples. There are many with Scala examples, of course, though you may wish to consider other tasks as well, for ideas.
There's lot of cool things to learn about Scala, but one has to be careful at beginner level. For instance, I would not speak of dependency injection (self types and the cake pattern) or of type classes (the pattern that simulates such with implicits).
Do look as well at the material on the Scala Lang site, particularly the Scala by Example document.
EDIT
I have now overseen several Scala dojos, so here's a bit of stuff I've learned from then:
Problems: they have to be fun, not-quite-easy, not-that-hard, and that has to be everyone's opinion.
We use the Dojo Puzzles site, which is in Portuguese so it won't be of use for most people here. If there's a similar site in English, I'd love to hear about it.
The way it works is you ask for a random problem, look it over and discuss to see if you'll pick it up or not, and then indicate by saying you'll use it, you'll not use it, or maybe you'll use it but you'd like to see another one. This vote gets registered and you can see how many people picked up a problem, which helps deciding whether to pick it up or not in first place.
Scala knowledge: it turns out it's not that important to introduce key concepts of Scala language beforehand, particularly if some of the participants have basic knowledge.
In my experience, setting up the testing environment with a trivial "pass" test and explaining how people should write the tests is often enough to get people started. If you feel someone is struggling to write something, give a quick explanation and get on with it.
Teaching Scala: if you do set out to teach Scala, keep lessons short and follow up with a dojo. In this case, keep a set of dojo problems that are adequate to the lesson, and, depending on how many lessons you want in one day, short.
It helps imposing artificial constraints on how one must solve a problem. Some examples of constraints I have put in practice are no classes and single-expression methods (that is, no multiple statements or val/var declarations). The point of these constraints is making it impossible for people to solve the problem in the way they are used to, which gets them to explore the language in search of alternatives.
I have the final results of three dojos done at my current job in this repository.
At the moment we are using the Randori Kata format, but without fixed time or break, and with retrospective at the end of the dojo, not at the beginning of the next. This, however, is just were we are currently at -- we have experimented many variations, and we are still evolving.
Perhaps you could have a look at the Ruby Quiz material for inspiration.
Take a look at Scala by example from Martin Odersky (creator of scala)
I have been using an Object-Oriented MVC architecture for a web project, and all the models are OO Perl. But I have noticed a couple on the team are reverting to procedural techniques and are essentially using "objects" as dumping grounds for related functions. Their functions basically read/write directly to/from the database.
What's the best way to convince them this is the wrong way? Are there some good tutorials I can get them to read?
I can think of three possible reasons why some team members may not produce nice OO code:
They don't care
They care, try to do it right but lack skills to do it right
They are doing it right, or at least right enough! Some matters of design are matters of opinion. Go back and look at some of your own old code, code that you thought was quite good, there's a good chance that you would revise some of it now.
My approach is to make the assumption that everybody wants to do the job right, so I assume (or pretend to assume) that folks care. One tries to build an ethos of wanting to do it right.
So that leaves building our skills, theirs and yours (and mine). Code reviews seem like one obvious way to do this. Talk about alternatives. Also maybe pair-programming?
OOP is just a tool to accomplish some great things like more reliable, usable and maintainable software. If you can not convince your team to write tests give up with strict OOP.
Are they all out of step with you? Perhaps it's just you who is out of step!
Lest I seem facetious, I mean what are the answers to the following questions:
What has the team agreed should be the approach?
Whose responsibility is it to enforce purity? If you don't go for enforced purity, whose responsibility is it to encourage purity? If it's not you, have a look in the mirror and make sure you are not the annoying noob on the team telling the old sweats how to do the jobs they've been doing since you were in Perl baby-clothes.
What mechanisms do you have in place for sorting out such team issues? Regular code reviews, pair programming, bare-knuckle fights ?
Asking them to read some tutorials is likely to be a waste of breath. What are your arguments for doing things the OO way? As Boris has observed, OO is not an end in itself, it is only a means to an end, and not the only means.
There are probably more things you want to consider in your situation, but these should get you started.