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• Writing a DB Python or Ruby

  - by WojonsTech

  I am planning on writing a database. I know it's crazy and people will tell me there is no good reason to do so. I am really using it to get better at programming overall, this database wont be used in production. I am planning on writing it Ruby or Python. I have some experience with both languages, but no job or large project experience. I don't want this to be a this is better than that randomly I really need some facts. The things that I need to know are which of the language are better at the following things. Searching arrays/hashes? Sorting? Threading? Sockets? Memory management? Disk Reads/Writes? base64 encode/decode? Again this is just a project for myself. I will port it on github for the hell of it, but I don't expect it to be amazing or going up against mysql or mongodb any day.

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• Which is a better practice - helper methods as instance or static?

  - by Ilian Pinzon

  This question is subjective but I was just curious how most programmers approach this. The sample below is in pseudo-C# but this should apply to Java, C++, and other OOP languages as well. Anyway, when writing helper methods in my classes, I tend to declare them as static and just pass the fields if the helper method needs them. For example, given the code below, I prefer to use Method Call #2. class Foo { Bar _bar; public void DoSomethingWithBar() { // Method Call #1. DoSomethingWithBarImpl(); // Method Call #2. DoSomethingWithBarImpl(_bar); } private void DoSomethingWithBarImpl() { _bar.DoSomething(); } private static void DoSomethingWithBarImpl(Bar bar) { bar.DoSomething(); } } My reason for doing this is that it makes it clear (to my eyes at least) that the helper method has a possible side-effect on other objects - even without reading its implementation. I find that I can quickly grok methods that use this practice and thus help me in debugging things. Which do you prefer to do in your own code and what are your reasons for doing so?

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• Advice on developing a social network [on hold]

  - by Siraj Mansour

  I am doing research on assembling a team, using the right tools, and the cost to develop a highly responsive social network that is capable of dealing with a lot of users. Similar to the Facebook concept but using the basics package for now. Profile, friends, posts, updates, media upload/download, streaming, chat and Inbox messaging are all in the package. We certainly do not expect it to be as popular as Facebook or handle the same number of users and requests, but in its own game it has to be a monster, and expandable for later on. Neglecting the hosting, and servers part, i am looking for technical advise and opinions, on what kind of team i need ? how many developers ? their expertise ? What are the right tools ? languages ? frameworks ? environments ? Any random ideas about the infrastructure ? Quick thoughts on the development process ? Please use references, if you have any to support your ideas. Development cost mere estimation ? NEGLECTING THE COST OF SERVERS I know my question is too broad but my knowledge is very limited and i need detailed help, for any help you can offer i thank you in advance.

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• How to recover broken dpkg after lucid-bleed ppa-purge?

  - by TryTryAgain

  Did a ppa-purge of lucid-bleed and dpkg didn't downgrade properly and now it is broken. dpkg: PreDepends: tar (>= 1.23) but 1.22-2ubuntu1 is to be installed What scares me is when simulating the removal of dpkg I get: Removing this package may render the system unusable. Are you sure you want to do that? and then the list of packages which depend on it, which will also be removed, is obviously very long. Is it safe for me to remove dpkg just to reinstall it? How would I ensure the list of packages which were also removed are then reinstalled? Will forcing the version of dpkg help? (FYI: simulating a forced version brings up a much smaller list of applications which will also be removed). Any other suggestions? Additional information based on comments: ppa-purge log: http://pastebin.com/1kT8cLvP If I sudo apt-get install dpkg=1.15.5.6ubuntu4.5 I get The following packages have unmet dependencies: libdpkg-perl: Depends: dpkg (= 1.15.8) but 1.15.5.6ubuntu4.5 is to be installed which sucks because that means more would be broken after doing so...but when I force the version through Synaptic I get: To be removed alien, build-essential, cdbs, checkinstall, debhelper, devscripts, dpkg-dev, google-earth-stable, googleearth-package, libdpkg-perl, lintian, lsb, lsb-core, lsb-cxx, lsb-desktop, lsb-graphics, lsb-languages, lsb-multimedia, lsb-printing, lsb-qt4, lsb-security, ubuntu-dev-tools.

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• Hosting several HTTP servers on single domain name

  - by Nakilon

  Several people have got a single domain name server.company.com server, where they are now supposed to host their infrastructure or temporal projects, written in different ways even in different programming languages. How do they divide the domain? Split into subdomains: john.server.company.com, kate.server.company.com, etc. This would need a lot of admins' assistance, time, etc. -- there would be no way for John and Kate to do it themselves. Split into url namespaces: server.company.com/john/, server.company.com/kate/, etc. Pro: They now can make a single welcome page at root with any additional info (if they need?) Con: Each server would need to know their namespace string constant, and hrefs like / whould need patching. Split into ports: server.company.com:8080, server.company.com:8081, etc. and make a single :80 welcome page. Pro: They still can make a single welcome page at :80 Con: ??? I would like to know more pros and cons for 2 and 3 solution.

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• Need theoretical help, how to comprehend an if-else dependency net

  - by macbie

  I am going to face a following issue: I'm writing a program that manages some properties, some of them are general and some are specific. Each property is a pair of key and value, and for example: if it is given a general property and other specific property with exactly the same key and value has been existed before then the general property will swap the specific one in the register. If there are two the same general properties - both will remain in the register. And so on; it is like a net of dependencies. In my case I can handle with it intuitively and foresee all cases, but only because the system is not too vast. What if it would? I have met such problems a few times in many different programs and languages (i.e working with C semaphores) and my question is: How to approach this kind of problem? Is this connected with finite state machine, graph theory or something similar? How to be sure that I have considered the whole system and each possible case? Could you recommend some resources (books, sites) to learn from?

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• Multilingual website without language component in the URL

  - by user359650

  I'm working on a website for Canada which will have French and English versions. For SEO purposes, I would like to avoid using any language tag in URLs because I believe it will have more impact (e.g. example.ca/products better than en.example.ca/products or example.ca/en/products). I believe this is technically possible because the2 languages are sufficiently different that the URLs won't be conflicting with one another (e.g. if you want a "product" page, it will be /products in English, and /produits in French so you know which language the URL is about). Since Google (and most likely others) doesn't rely on the URL (nor HTML tags) to determine the content language I don't see any problems with search engines. To make this possible I've thought about using a cookie distinct from the session cookie (e.g. example.org_language) with long term expiry (e.g. N years) that will memorize the language chosen by the user. That way when people visit the website with a new browser session, they get served the proper language. I have already given up on users being able to switch one page from English to French: when people will chose English or French from the menu they will be redirected to the corresponding version of the home page. Do you foresee any problems with not using a language component in the URL (whether domain or path)? (as long as one makes sure URLS don't conflict).

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• good literature for teaching object oriented thinking in C [closed]

  - by Dipan Mehta

  Quite often C is the primary platform for the development. And when things are large scale, I have seen partitioning of the system as different objects is quite a natural thing. Some or many of the object orientated analysis and design principles are used here very well. This is not a debate question about whether or not C is a good candidate for object oriented programming or not. This is also NOT a question how to do OO in C. You can refer to this question and there are probably many such citations. As far as I am concerned, I have learned some of this things while working with many open source and commercial projects. (libjpeg, ffmpeg, Gstreamer which is based on GObject). I can probably extend a few references that explains some of these concepts such as - 1. Event Helix article, 2. Linux Mag article 3. one of my answers which links Schreiner's reference. Unfortunately, when we induct younger folks, it seems too hard to make them learn all of it the hard way. Usually, when we say it's C, a general reaction is to throw away all of the "Object thinking". Looking for help extending above references from those who have been in the similar areas of work. Are there any good formal literature that explains how Object thinking can be made to use while you are working in C? I have seen tons of book on general "object oriented paradigms" but they all focus on advanced languages mostly not in C. You see most C books - but most focus only on the syntax and the obfuscated corners of C and that's it. There are hardly ANY good reference, specially books or any systematic (I mean formal) literature on how to apply OO in C. This is very surprising given that so many large scale open source projects use C which are truly using this very well; but we hardly see any good formal literature on this subject.

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• where to start and lack of motivation

  - by anoguy

  I have a few questions that have been bothering me for quite a while, maybe you guys can give me some tips. So let me give a very brief explanation about what I am doing at the moment (like someone cares lol). At the moment I am a last year student on computer science. And like most of you already know is that you won't learn deep programming there, you need to learn it yourself. So at the moment I know like the basics of c++, java, html, php. But it's all bits of this and bits of that. I seriously want to dive deeper in the programming world but there are so many programming languages on the web and there is so much information that i don't know where to start any more.. And that's not the biggest issue, I also lost a bit of my motivation for programming and I like to get more motivation for it so that I love what I do (I am also a very lazy person btw, that's also a problem playing here). So can you guys give me some tips for helping me, because I really want to get pumped up and make cool stuff. (sry for my bad english XD)

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• Why are embedded device apps still written in C/C++? Why not Java programming language?

  - by hinkmond

  At the recent Black Hat 2014 conference in Sin City, the Black Hatters were focusing on Embedded Devices and IoT. You know? Make your networked-toaster burn your bread 10,000 miles away, over the Web for grins and giggles. Well, apparently the Black Hatters say it can be done pretty easily these days, which is scary. See: Securing Embedded Devices & IoT Here's a quote: All these devices are still written in C and C++. The challenges associated with developing securely in these languages have been fought for nearly two decades. "You often hear people say, 'Well, why don't we just get rid of the C and C++ language if it's so problematic. Why don't we just write everything in C# or Java, or something that is a little safer to develop in?'," DeMott says. Gah! Why are all these IoT devices still using C/C++? Of course they should be using Java SE Embedded technology! It's a natural fit to use for better security on embedded devices. Or, I guess, developers really don't mind if their networked-toasters do char their breakfast. If it can be burned, it will be... That's what I say. Unless they use Java. Hinkmond

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• What's the proper term for a function inverse to a constructor? Deconstructor, destructor, or something else?

  - by Petr Pudlák

  Edit: I'm rephrasing the question a bit. Apparently I caused some confusion because I didn't realize that the term destructor is used in OOP for something quite different - it's a function invoked when an object is being destroyed. In functional programming we (try to) avoid mutable state so there is no such equivalent to it. (I added the proper tag to the question.) Instead, I've seen that the record field for unwrapping a value (especially for single-valued data types such as newtypes) is sometimes called destructor or perhaps deconstructor. For example, let's have (in Haskell): newtype Wrap = Wrap { unwrap :: Int } Here Wrap is the constructor and unwrap is what? I've seen both, for example: ... Most often, one supplies smart constructors and destructors for these to ease working with them. ... at Haskell wiki, or ... The general theme here is to fuse constructor - deconstructor pairs like ... at Haskell wikibook (here it's probably meant in a bit more general sense). The questions are: How do we call unwrap in functional programming? Deconstructor? Destructor? Or by some other term? And to clarify, is this terminology applicable to other functional languages, or is it used just in the Has

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• Hidden Gems: Accelerating Oracle Data Integrator with SOA, Groovy, SDK, and XML

  - by Alex Kotopoulis

  On the last day of Oracle OpenWorld, we had a final advanced session on getting the most out of Oracle Data Integrator through the use of various advanced techniques. The primary way to improve your ODI processes is to choose the optimal knowledge modules for your load and take advantage of the optimized tools of your database, such as OracleDataPump and similar mechanisms in other databases. Knowledge modules also allow you to customize tasks, allowing you to codify best practices that are consistently applied by all integration developers. ODI SDK is another very powerful means to automate and speed up your integration development process. This allows you to automate Life Cycle Management, code comparison, repetitive code generation and change of your integration projects. The SDK is easily accessible through Java or scripting languages such as Groovy and Jython. Finally, all Oracle Data Integration products provide services that can be integrated into a larger Service Oriented Architecture. This moved data integration from an isolated environment into an agile part of a larger business process environment. All Oracle data integration products can play a part in thisracle GoldenGate can integrate into business event streams by processing JMS queues or publishing new events based on database transactions. Oracle GoldenGate can integrate into business event streams by processing JMS queues or publishing new events based on database transactions. Oracle Data Integrator allows full control of its runtime sessions through web services, so that integration jobs can become part of business processes. Oracle Data Service Integrator provides a data virtualization layer over your distributed sources, allowing unified reading and updating for heterogeneous data without replicating and moving data. Oracle Enterprise Data Quality provides data quality services to cleanse and deduplicate your records through web services.

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• Are R&D mini-projects a good activity for interns?

  - by dukeofgaming

  I'm going to be in charge of hiring some interns for our software department soon (automotive infotainment systems) and I'm designing an internship program. The main productive activity "menu" I'm planning for them consists of: Verification testing Writing Unit Tests (automated, with an xUnit-compliant framework [several languages in our projects]) Documenting Code Updating wiki Updating diagrams & design docs Helping with low priority tickets (supervised/mentored) Hunting down & cleaning compiler/run-time warnings Refactoring/cleaning code against our coding standards But I also have this idea that having them do small R&D projects would be good to test their talent and get them to have fun. These mini-projects would be: Experimental implementations & optimizations Proof of concept implementations for new technologies Small papers (~2-5 pages) doing formal research on the previous two points Apps (from a mini-project pool) These kinds of projects would be pre-defined and very concrete, although new ideas from the interns themselves would be very welcome. Even if a project is too big or is abandoned, the idea would also be to lay the ground work so they can be retaken by another intern or intern team. While I think this is good in concept, I don't know if it could be good in practice, as obviously this would diminish their productivity on "real work" (work with immediate value to the company), but I think it could help bring aboard very bright people and get them to want to stay in the future (which, I think, is the end goal for any internship program). My question here is if these activities are too open ended or difficult for the average intern to accomplish and if R&D is an efficient use of an interns time or if it makes more sense for to assign project work to interns instead.

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• Code base migration - old versioning system to modern

  - by JohnP

  Our current code base is contained in a versioning system that is old and outdated (Visual Sourcesafe 5.0, mid 1990's), and contains a mix of packages that are no longer used, ones that are being used but no longer updated, and newer code. It is also a mix of 4 languages, and includes libraries for some of our systems (Such as Dialogic, Sun Tzu {clipper}) implementations. This breaks down into the following categories: Legacy code - No longer used (Systems that have been retired or replaced, etc) Legacy code - In current use (No intentions for upgrades or minor bug fixes, only major fixes if needed) Current code - In current use, and will be used for future versions/development Support libraries - For both legacy and current code (Some of the legacy libraries are no longer available as well) We would like to migrate this to a newer versioning system as we will be adding more developers, and expanding the reach to include remote programmers. When migrating, how do you structure it? Do you just perform a dump of all the data and then import it into the new system, or do you segregate according to type before you bring it into the new system? Do you set up a separate area for libraries, or keep them with the relevant packages? Do you separate by language, system, both? A general outline and methodology is fine, it doesn't need to be broken down to individual program level.

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• Open Source Projects for Beginning Coders?

  - by MattDMo

  After working as a molecular biologist at the bench for many years, I lost my job last year and am thinking about a career change. I've been using open-source software and doing Linux system administration since the mid 90s, and have written/improved some small shell/Perl/PHP scripts, and am very comfortable building from source, but never progressed to creating non-trivial programs de novo. I want to move to actually learning real programming skills and contributing back to the community, with the possible eventual goal of getting into bioinformatics as a career in the future. I'm a stay-at-home dad now, so I have some time on my hands. I've done a lot of research on languages, and have settled on Python as my major focus for now. I'm set up on GitHub, but haven't forked anything yet. I've looked around OpenHatch some, but nothing really grabbed me. I've heard the advice to work on what you use/love, but that category is so broad that I'm having trouble finding any one thing to get started on. What are your suggestions for getting started? How do you pick a project that will welcome your (possibly amateurish) help? With a fairly limited skill set, how do you find a request that you can handle? What are common newbie mistakes to avoid? Any other advice?

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• That Tool is cURLy

  When you just use IE, Firefox or Chrome it can be easy to forget that HTTP is about more then just going to check the latest tech news at Engadget. It is a full and rich protocol, and a great way to experience that richness is the powerful command line utility cURL. cURL has a lot of options, but the syntax starts out simple. You can retrieve the contents of a web page with a simple curl http://blogs.claritycon.com/. The results should be the full text of the web page, tags and all. From there, you can use X to specify the HTTP verb to use, POST, PUT, DELETE, PATCH, etc and d to specify the payload of a POST or PUT. I have found cURL to be incredibly useful for two scenarios. First, as a good way to test basic web services. Second, while working a bit with CouchDB and another document based database, cURL has helped me learn more about RESTful APIs, including different verbs and response codes. cURL is a mainstay in our environments and programming languages precisely because it is simple, powerful and discoverable. I encourage more .NET developers to take a look, bask on the command line for a while and enjoy the plain text of the web. And this excellent logo:     -- Relevant Links -- Its not always the case with manuals, but the manual for cURL is quite useful: http://curl.haxx.se/docs/manual.html To make your command line look a little nicer (and more powerful) on Windows, check out Console and add some transparency effects: http://sourceforge.net/projects/console/Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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• Composing programs from small simple pieces: OOP vs Functional Programming

  - by Jay Godse

  I started programming when imperative programming languages such as C were virtually the only game in town for paid gigs. I'm not a computer scientist by training so I was only exposed to Assembler and Pascal in school, and not Lisp or Prolog. Over the 1990s, Object-Oriented Programming (OOP) became more popular because one of the marketing memes for OOP was that complex programs could be composed of loosely coupled but well-defined, well-tested, cohesive, and reusable classes and objects. And in many cases that is quite true. Once I learned object-oriented programming my C programs became better because I structured them more like classes and objects. In the last few years (2008-2014) I have programmed in Ruby, an OOP language. However, Ruby has many functional programming (FP) features such as lambdas and procs, which enable a different style of programming using recursion, currying, lazy evaluation and the like. (Through ignorance I am at a loss to explain why these techniques are so great). Very recently, I have written code to use methods from the Ruby Enumerable library, such as map(), reduce(), and select(). Apparently this is a functional style of programming. I have found that using these methods significantly reduce code volume, and make my code easier to debug. Upon reading more about FP, one of the marketing claims made by advocates is that FP enables developers to compose programs out of small well-defined, well-tested, and reusable functions, which leads to less buggy code, and low code volume. QUESTIONS: Is the composition of complex program by using FP techniques contradictory to or complementary to composition of a complex program by using OOP techniques? In which situations is OOP more effective, and when is FP more effective? Is it possible to use both techniques in the same complex program? Do the techniques overlap or contradict each other?

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• Why job postings always looking for "rockstars?"

  - by Xepoch

  I have noticed a recent trend in requesting programmers who are rockstars. I get it, they're looking for someone who is really good at what they do. But why (pray) make the reference to a rockstar? Do these companies really want these traits as a real rockstar? Party all night and wake up to take care of quick business in the morning? Substance abuse, Narcissism with celebrity, Compensation well exceeding their management, Excellent at putting on a short-lived show, Entertainment instead of value, 1 hit (project) wonders or single-genre performers, Et cetera What is wrong with Senior or Principal Software Engineer who has an established and proven passion for the business? Rather do we mean quite the opposite, someone who: rolls up the sleeves and gets to work, takes appropriate direction and helps influence teams, programs in lessons' learned and proper practices, provides timely communication to the whole team, can code and understand multiple languages, understands the science and theory behind computation, Is there a trend to diversify the software engineering ranks? How many software rockstars can you hire before your band starts breaking up? Sure, there are lots of folks doing this stuff on their own, maybe even a rare few who do coding for show, but I wager the majority is for business. I don't see ads for rockstar accountants, or rockstar machinists, or rockstart CFOs. What makes the software programmer and their hiring departments lean towards this kind of job title?

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• How to avoid game objects accidentally deleting themselves in C++

  - by Tom Dalling

  Let's say my game has a monster that can kamikaze explode on the player. Let's pick a name for this monster at random: a Creeper. So, the Creeper class has a method that looks something like this: void Creeper::kamikaze() { EventSystem::postEvent(ENTITY_DEATH, this); Explosion* e = new Explosion; e->setLocation(this->location()); this->world->addEntity(e); } The events are not queued, they get dispatched immediately. This causes the Creeper object to get deleted somewhere inside the call to postEvent. Something like this: void World::handleEvent(int type, void* context) { if(type == ENTITY_DEATH){ Entity* ent = dynamic_cast<Entity*>(context); removeEntity(ent); delete ent; } } Because the Creeper object gets deleted while the kamikaze method is still running, it will crash when it tries to access this->location(). One solution is to queue the events into a buffer and dispatch them later. Is that the common solution in C++ games? It feels like a bit of a hack, but that might just be because of my experience with other languages with different memory management practices. In C++, is there a better general solution to this problem where an object accidentally deletes itself from inside one of its methods?

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• Interview questions for programming tutor?

  - by Emmett Gear

  My family is looking for a programming/computer science tutor. Personally, I want to learn Java or some other brand of web programming. I am best described as a PC "power user." I have never programmed in the past and would like a good jump start. I am a very quick learner and do not expect the tutor to have to teach me the ultra basic stuff that I can learn myself. My son also needs a programming tutor. He just got into Carnegie Mellon as a computer science major. Having done only robotics and mathematics in the past he is very nervous that he does not have the same level of knowledge as his future classmates. I need some help coming up with a list of questions to ask potential tutors and some criteria to judge them by. Thanks! Edit: So far I have come up with just the obvious... Where did you receive your education? What languages are you familiar with? How long have you been tutoring? What made you decide to become a tutor? What software projects have you worked on? What work references can you give me? How much do you charge?

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• Oracle ADF and Simplified UI Apps: I18n Feng Shui on Display

  - by ultan o'broin

  I demoed the Hebrew language version of Oracle Sales Cloud Release 8 live in Israel recently. The crowd was yet again wowed by the simplified UI (SUI). I’ve now spent some time playing around with most of the 23 language versions, or the NLS (Natural Language Support) versions as we’d call them, available in Release 8. Hebrew Oracle Sales Cloud Release 8 The simplified UI is built using 100% Oracle ADF. This framework is a great solution for developers to productively build tablet-first, mobility-driven apps for users who work and live using natural languages other than English. Oracle ADF’s internationalization (i18n) relies on built-in Java and Unicode,  packing in i18n goodness such as Bi-Di (or bi-directional) flipping of pages, locale-enabled resource bundles, date and time support, and so on. Comparing German (left) and Hebrew Bi-Di (right) page components in the simplified UI. Note the change in the direction of the arrows and positions of the text. So, developers who need to build global apps don’t have to do anything special when using Oracle ADF components, all thanks to the baked-in UX Feng Shui, as Grant Ronald of the ADF team would say to the UK Oracle User Group. Find out more  about  ADF i18n from Frédéric Desbiens (@blueberrycoder)  on the ADF Architecture TV channel.

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• Where to Start?

  - by freemann098

  my name is Chase. I've been programming for over 3 years now and I've made very little progress towards game development. I blame myself for it due to reasons. I have experience in many languages such as C++, C#, and Java. I have a little bit of knowledge in JavaScript/HTML and Python. My question is where to start on actually understanding jumping into game development. Whenever I watch game development tutorials it mostly makes sense until points of things like OpenGL or advanced topics that make no sense at all. An example is something like glOrhho Matrix or whatever. Videos either don't explain things like this or they're not explained very well. Do I not know enough basics? I find myself always copying code from a video but understanding very little of it. It's like i'm memorizing things I don't understand which makes it hard to program at all. If I were to want to get to the point where I could write my own game engine or just a game by myself in general in C++ using at the most documentation how would I start at mastering to that level. Should I learn C first, or get really good at basics in general with C++. I know there is a similar posted question on this site but it's not the same due to the fact the person asking the question has a well knowledge level in programming. I'm stuck in a loop of learning the same things but if I go farther I don't understand. I'm stuck in the same spot and need to make progress.

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• Functional programming compared to OOP with classes

  - by luckysmack

  I have been interested in some of the concepts of functional programming lately. I have used OOP for some time now. I can see how I would build a fairly complex app in OOP. Each object would know how to do things that object does. Or anything it's parents class does as well. So I can simply tell Person().speak() to make the person talk. But how do I do similar things in functional programming? I see how functions are first class items. But that function only does one specific thing. Would I simply have a say() method floating around and call it with an equivalent of Person() argument so I know what kind of thing is saying something? So I can see the simple things, just how would I do the comparable of OOP and objects in functional programming, so I can modularize and organize my code base? For reference, my primary experience with OOP is Python, PHP, and some C#. The languages that I am looking at that have functional features are Scala and Haskell. Though I am leaning towards Scala. Basic Example (Python): Animal(object): def say(self, what): print(what) Dog(Animal): def say(self, what): super().say('dog barks: {0}'.format(what)) Cat(Animal): def say(self, what): super().say('cat meows: {0}'.format(what)) dog = Dog() cat = Cat() dog.say('ruff') cat.say('purr')

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• Are first-class functions a substitute for the Strategy pattern?

  - by Prog

  The Strategy design pattern is often regarded as a substitute for first-class functions in languages that lack them. So for example say you wanted to pass functionality into an object. In Java you'd have to pass in the object another object which encapsulates the desired behavior. In a language such as Ruby, you'd just pass the functionality itself in the form of an annonymous function. However I was thinking about it and decided that maybe Strategy offers more than a plain annonymous function does. This is because an object can hold state that exists independently of the period when it's method runs. However an annonymous function by itself can only hold state that ceases to exist the moment the function finishes execution. So my question is: when using a language that features first-class functions, would you ever use the Strategy pattern (i.e. encapsulate the functionality you want to pass around in an explicit object), or would you always use an annonymous function? When would you decide to use Strategy when you can use a first-class function?

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• Can higher-order functions in FP be interpreted as some kind of dependency injection?

  - by Giorgio

  According to this article, in object-oriented programming / design dependency injection involves a dependent consumer, a declaration of a component's dependencies, defined as interface contracts, an injector that creates instances of classes that implement a given dependency interface on request. Let us now consider a higher-order function in a functional programming language, e.g. the Haskell function filter :: (a -> Bool) -> [a] -> [a] from Data.List. This function transforms a list into another list and, in order to perform its job, it uses (consumes) an external predicate function that must be provided by its caller, e.g. the expression filter (\x -> (mod x 2) == 0) [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] selects all even numbers from the input list. But isn't this construction very similar to the pattern illustrated above, where the filter function is the dependent consumer, the signature (a -> Bool) of the function argument is the interface contract, the expression that uses the higher-order is the injector that, in this particular case, injects the implementation (\x -> (mod x 2) == 0) of the contract. More in general, can one relate higher-order functions and their usage pattern in functional programming to the dependency injection pattern in object-oriented languages? Or in the inverse direction, can dependency injection be compared to using some kind of higher-order function?

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