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  • Floating point undesireable in highly critical code?

    - by Kirt Undercoffer
    Question 11 in the Software Quality section of "IEEE Computer Society Real-World Software Engineering Problems", Naveda, Seidman, lists fp computation as undesirable because "the accuracy of the computations cannot be guaranteed". This is in the context of computing acceleration for an emergency braking system for a high speed train. This thinking seems to be invoking possible errors in small differences between measurements of a moving object but small differences at slow speeds aren't a problem (or shouldn't be), small differences between two measurements at high speed are irrelevant - can there be a problem with small roundoff errors during deceleration for an emergency braking system? This problem has been observed with airplane braking systems resulting in hydroplaning but could this actually happen in the context of a high speed train? The concern about fp errors seems to not be well-founded in this context. Any insight? The fp is used for acceleration so perhaps the concern is inching over a speed limit? But fp should be just fine if they use a double in whatever implementation language. The actual problem in the text states: During the inspection of the code for the emergency braking system of a new high speed train (a highly critical, real-time application), the review team identifies several characteristics of the code. Which of these characteristics are generally viewed as undesirable? The code contains three recursive functions (well that one is obvious). The computation of acceleration uses floating point arithmetic. All other computations use integer arithmetic. The code contains one linked list that uses dynamic memory allocation (second obvious problem). All inputs are checked to determine that they are within expected bounds before they are used.

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  • If you had two projects with the same specification and only one was developed using TDD how could you tell?

    - by Andrew
    I was asked this question in an interview and it has been bugging me ever since. You have two projects, both with the same specification but only one of these projects was developed using Test Driven Development. You are given the source for both but with the tests removed from the TDD project. How can you tell which was developed using TDD? All I was able to muster up was something about the classes being more 'broken up' in to smaller chunks and having more visible APIs, not my proudest moment. I would be very interested to hear a good answer to this question.

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  • How can you predict the time it will take for two processes in two different machines in a cluster to communicate?

    - by Dokkat
    I am trying to develop a computing application which needs a lot of memory (500gb). Buying a single machine for that is overly expensive. I can, though, buy ~100 small instances on Digital Ocean or similar, divide the memory in blocks and use TCP to emulate shared memory between the instances. Now, my question is: how can I measure/predict the time it will take for two processes in two different machines like that to share information, in comparison to IPC and shared memory? Are there rules of thumb? I don't want exact values, but knowing more or less how much faster one is would be very helpful in visualising the feasibility of this approach.

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  • Open Source programs for learning C#

    - by dizzytri99er
    I was wondering if there are any good open source programs out there that are basically 'all-skill' encompassing that i could use to develop my skills Im a strong believer in learning by doing so a nice open source program i could load onto my machine to learn C# would be ideal. I have some knowledge with basic C# and a little more advanced techniques so im not a total beginner i realise similar questions have been asked before but i was just trying no see if there is one definitive one rather than lots of little projects hopefully im not asking too much! haha

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  • 0.00006103515625 GB of RAM. Is .NET MicroFramework part of Windows CE?

    - by Rocket Surgeon
    The .NET MicroFramework claims to work on 64K RAM and has list of compatible targets vendors. At the same time, same vendors who ship hardware and create Board Support Packages (vendors like Adeneo) keep releasing something named Windows 7 CE BSP for the same hardware targets. Obviously the OS as heavy as WinCE needs more than 64K RAM. So, somehow .NET MicroFramework is relevant to WinCE, but how ? Is it part of bigger OS or is it base of it, or are both mutually exclusive ? Background: 0.00006103515625 GByte of RAM is same as 64Kbyte of RAM. I am looking for possiblity to use Microsoft development tools for small target like BeagleBone. http://www.adeneo-embedded.com/About-Us/News/Release-of-TI-BeagleBone Nice. Now .. where is a MicroFramework for the same beaglebone ? Is it inside the released pile ?

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  • Implementing a bit shift using AND, NOT, ADD [closed]

    - by fdart17
    I'm implementing a 16-bit left bit shift by r bits, and I only have access to AND, NOT and ADD. There are 3 condition codes, negative, zero and positive, which are set when you use any of these operations. How I went about it was : (1) And the number with 1000 0000 0000 0000 to set condition codes to positive if the most significant bit is 1. (2) Add the number with itself. This shifts bits one to the left. (3) If the MSB was 1, add 1 to the result. (4) Loop threw (1)-(3) r times. I'm wondering if anyone has any hints to some more efficient methods? Thanks!

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  • .Net Application & Database Modularity/Reuse

    - by Martaver
    I'm looking for some guidance on how to architect an app with regards to modularity, separation of concerns and re-usability. I'm working on an application (ASP.Net, C#) that has distinctly generic chunks of functionality, that I'd love to be able to lift out, all layers, into re-usable components. This means the module handles the database schema, data access, API, everything so that the next time I want to use it I can just register the module and hook into it. Developing modules of re-usable functionality is a no-brainer, but what is really confusing me is what to do when it comes to handling a core re-usable database schema that serves the module's functionality. In an ideal world, I would register a module and it would ensure that the associated database schema exists in the DB. I would code on the assumption that the tables exist, calling the module's functionality through the DLL, agnostic of the database layer. Kind of like Enterprise Library's Caching/Logging Application Block, which can create a DB schema in the target DB to use as a data store. My Questions is: What do you think is the best way to achieve this, firstly, in terms design architecture, and secondly solution structure. What patterns/frameworks do you know that exist & support this kind of thing? My thoughts so far: I mostly use Entity Framework and SQL Server DB Projects. I thought about a 'black box' approach to modules of functionality. I could use use a code-first approach in EF4, and use the ObjectContext to create a database when the module is initialized. However this means that all of the entities that my module encapsulates would be disconnected from the rest of the application because they belonged to an abstracted ObjectContext. Further - Creating appropriate indexes and references between domain entities and the module's entities would be impossible to do practically. I've thought of adopting Enterprise Library and creating my own Application Blocks. I'm not sure how this would play nice with Entity Framework (if at all) though. I like the idea of building on proven patterns & practices to encapsulate established, reusable functionality. I thought of abandoning Entity Framework for the Module, and just creating a separate DB schema for the module with its own set of stored procedures & ADO.Net. Then deploying the script at run-time if interrogation shows that it doesn't exist. But once again, for application developing outside of the application, I would want to use Entity Framework and I would have to use the module separately, disconnected from the domain ObjectContext. Has anyone had experience developing these sorts of full-stack modules? What advice can you offer? Am I biting off more than I can chew?

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  • Masters vs. PhD - long [closed]

    - by Sterling
    I'm 21 years old and a first year master's computer science student. Whether or not to continue with my PhD has been plaguing me for the past few months. I can't stop thinking about it and am extremely torn on the issue. I have read http://www.cs.unc.edu/~azuma/hitch4.html and many, many other masters vs phd articles on the web. Unfortunately, I have not yet come to a conclusion. I was hoping that I could post my ideas about the issue on here in hopes to 1) get some extra insight on the issue and 2) make sure that I am correct in my assumptions. Hopefully having people who have experience in the respective fields can tell me if I am wrong so I don't make my decision based on false ideas. Okay, to get this topic out of the way - money. Money isn't the most important thing to me, but it is still important. It's always been a goal of mine to make 6 figures, but I realize that will probably take me a long time with either path. According to most online salary calculating sites, the average starting salary for a software engineer is ~60-70k. The PhD program here is 5 years, so that's about 300k I am missing out on by not going into the workforce with a masters. I have only ever had ~1k at one time in my life so 300k is something I can't even really accurately imagine. I know that I wouldn't have at once obviously, but just to know I would be earning that is kinda crazy to me. I feel like I would be living quite comfortably by the time I'm 30 years old (but risk being too content too soon). I would definitely love to have at least a few years of my 20s to spend with that kind of money before I have a family to spend it all on. I haven't grown up very financially stable so it would be so nice to just spend some money…get a nice car, buy a new guitar or two, eat some good food, and just be financially comfortable. I have always felt like I deserved to make good money in my life, even as a kid growing up, and I just want to have it be a reality. I know that either path I take will make good money by the time I'm ~40-45 years old, but I guess I'm just sick of not making money and am getting impatient about it. However, a big idea pushing me towards a PhD is that I feel the masters path would give me a feeling of selling out if I have the capability to solve real questions in the computer science world. (pretty straight-forward - not much to elaborate on, but this is a big deal) Now onto other aspects of the decision. I originally got into computer science because of programming. I started in high school and knew very soon that it was what I wanted to do for a career. I feel like getting a masters and being a software engineer in the industry gives me much more time to program in my career. In research, I feel like I would spend more time reading, writing, trying to get grant money, etc than I would coding. A guy I work with in the lab just recently published a paper. He showed it to me and I was shocked by it. The first two pages was littered with equations and formulas. Then the next page or so was followed by more equations and formulas that he derived from the previous ones. That was his work - breaking down and creating all of these formulas for robotic arm movement. And whenever I read computer science papers, they all seem to follow this pattern. I always pictured myself coding all day long…not proving equations and things of that nature. I know that's only one part of computer science research, but that part bores me. A couple cons on each side - Phd - I don't really enjoy writing or feel like I'm that great at technical writing. Whenever I'm in groups to make something, I'm always the one who does the large majority of the work and then give it to my team members to write up a report. Presenting is different though - I don't mind presenting at all as long as I have a good grasp on what I am presenting. But writing papers seems like such a chore to me. And because of this, the "publish or perish" phrase really turns me off from research. Another bad thing - I feel like if I am doing research, most of it would be done alone. I work best in small groups. I like to have at least one person to bounce ideas off of when I am brainstorming. The idea of being a part of some small elite group to build things sounds ideal to me. So being able to work in small groups for the majority of my career is a definite plus. I don't feel like I can get this doing research. Masters - I read a lot online that most people come in as engineers and eventually move into management positions. As of now, I don't see myself wanting to be a part of management. Lets say my company wanted to make some new product or system - I would get much more pride, enjoyment, and overall satisfaction to say "I made this" rather than "I managed a group of people that made this." I want to be a big part of the development process. I want to make things. I think it would be great to be more specialized than other people. I would rather know everything about something than something about everything. I always have been that way - was a great pitcher during my baseball years, but not so good at everything else, great at certain classes in school, but not so good at others, etc. To think that my career would be the same way sounds okay to me. Getting a PhD would point me in this direction. It would be great to be some guy who is someone that people look towards and come to ask for help because of being such an important contributor to a very specific field, such as artificial neural networks or robotic haptic perception. From what I gather about the software industry, being specialized can be a very bad thing because of the speed of the new technology. I When it comes to being employed, I have pretty conservative views. I don't want to change companies every 5 years. Maybe this is something everyone wishes, but I would love to just be an important person in one company for 10+ (maybe 20-25+ if I'm lucky!) years if the working conditions were acceptable. I feel like that is more possible as a PhD though, being a professor or researcher. The more I read about people in the software industry, the more it seems like most software engineers bounce from company to company at rapid paces. Some even work like a hired gun from project to project which is NOT what I want AT ALL. But finding a place to make great and important software would be great if that actually happens in the real world. I'm a very competitive person. I thrive on competition. I don't really know why, but I have always been that way even as a kid growing up. Competition always gave me a reason to practice that little extra every night, always push my limits, etc. It seems to me like there is no competition in the research world. It seems like everyone is very relaxed as long as research is being conducted. The only competition is if someone is researching the same thing as you and its whoever can finish and publish first (but everyone seems to careful to check that circumstance). The only noticeable competition to me is just with yourself and your own discipline. I like the idea that in the industry, there is real competition between companies to put out the best product or be put out of business. I feel like this would constantly be pushing me to be better at what I do. One thing that is really pushing me towards a PhD is the lifetime of the things you make. I feel like if you make something truly innovative in the industry…just some really great new application or system…there is a shelf-life of about 5-10 years before someone just does it faster and more efficiently. But with research work, you could create an idea or algorithm that last decades. For instance, the A* search algorithm was described in 1968 and is still widely used today. That is amazing to me. In the words of Palahniuk, "The goal isn't to live forever, its to create something that will." Over anything, I just want to do something that matters. I want my work to help and progress society. Seriously, if I'm stuck programming GUIs for the next 40 years…I might shoot myself in the face. But then again, I hate the idea that less than 1% of the population will come into contact with my work and even less understand its importance. So if anything I have said is false then please inform me. If you think I come off as a masters or PhD, inform me. If you want to give me some extra insight or add on to any point I made, please do. Thank you so much to anyone for any help.

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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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  • Techniques and methods to improve and speedup development

    - by Jlouro
    I just got a new project. It’s a WinForm app. And it’s interesting because I will have the possibility to learn how fish farms work and are managed. I will have to develop touch interfaces, and use datasnap to communicate and sync data between farm and office. The development will be done in DELPHI win32, still not sure about the database, but maybe SQLlite. So now comes the difficult part of the project, building it. I am just finishing one. It took me a lot of time to do it and I am a bit “burned out”. I will have time to relax, not much, but a few days. What I am looking is some tips and tricks and possibly tools to be able to speed up the development. It must be up and running in 2 months. So what tricks do you use to speed up things?

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  • Should I limit my type name suffix vocabulary when using OOP?

    - by Den
    My co-workers tend to think that it is better to limit non-domain type suffixes to a small fixed set of OOP-pattern inspired words, e.g.: *Service *Repository *Factory *Manager *Provider I believe there is no reason to not extend that set with more names, e.g. (some "translation" to the previous vocabulary is given in brackets): *Distributor (= *DistributionManager or *SendingService) *Generator *Browser (= *ReadonlyRepositoryService) *Processor *Manipulator (= *StateMachineManager) *Enricher (= *EnrichmentService) (*) denotes some domain word, e.g. "Order", "Student", "Item" etc. The domain is probably not complex enough to use specialized approaches such as DDD which could drive the naming.

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  • How to add precedence to LALR parser like in YACC?

    - by greenoldman
    Please note, I am asking about writing LALR parser, not writing rules for LALR parser. What I need is... ...to mimic YACC precedence definitions. I don't know how it is implemented, and below I describe what I've done and read so far. For now I have basic LALR parser written. Next step -- adding precedence, so 2+3*4 could be parsed as 2+(3*4). I've read about precedence parsers, however I don't see how to fit such model into LALR. I don't understand two points: how to compute when insert parenthesis generator how to compute how many parenthesis the generator should create I insert generators when the symbols is taken from input and put at the stack, right? So let's say I have something like this (| denotes boundary between stack and input): ID = 5 | + ..., at this point I add open, so it gives ID = < 5 | + ..., then I read more input ID = < 5 + | 5 ... and more ID = < 5 + 5 | ; ... and more ID = < 5 + 5 ; | ... At this point I should have several reduce moves in normal LALR, but the open parenthesis does not match so I continue reading more input. Which does not make sense. So this was when problem. And about count, let's say I have such data < 2 + < 3 * 4 >. As human I can see that the last generator should create 2 parenthesis, but how to compute this? After all there could be two scenarios: ( 2 + ( 3 *4 )) -- parenthesis is used to show the outcome of generator or (2 + (( 3 * 4 ) ^ 5) because there was more input Please note that in both cases before 3 was open generator, and after 4 there was close generator. However in both cases, after reading 4 I have to reduce, so I have to know what generator "creates".

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  • How should I practice web server administration?

    - by Astyanax
    Security students can practice their skills with software like OWASP's webgoat or something similar to "hackthissite". Students interested in Operating Systems can study MINIX and PintOS, write shell scripts or study POSIX system calls. What would be the best course of action in order to practice Server Administration? Is there any such software/resource available, teaching you such skills with small lessons, or it is totally up to you? I've practiced live FreeBSD server administration and management of VMs (CentOS, Gentoo, Debian) under VirtualBox, but I always feel that this isn't enough and I must push myself harder. So, what would you recommend? What has worked for you?

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  • Spring + JSR 303 Validation group is ignored [closed]

    - by nsideras
    we have a simple bean with JSR annotations public class CustomerDTO { private static final long serialVersionUID = 1L; private Integer id; @NotEmpty(message = "{customer.firstname.empty}") private String firstName; @NotEmpty(message = "{customer.lastname.empty}") private String lastName; @NotEmpty(groups={PasswordChange.class}, message="{password.empty}") private String password; @NotEmpty(groups={PasswordChange.class}, message="{confirmation.password.empty}") private String password2; } and we have a Spring Controller @RequestMapping(value="/changePassword", method = RequestMethod.POST) public String changePassword(@Validated({ PasswordChange.class }) @ModelAttribute("customerdto") CustomerDTO customerDTO, BindingResult result, Locale locale) { logger.debug("Change Password was submitted with information: " + customerDTO.toString()); try { passwordStrengthPolicy.checkPasswordStrength(locale, customerDTO.getPassword()); if (result.hasErrors()) { return "changePassword"; } logger.debug("Calling customer service changePassword: " + customerDTO); customerOnlineNewService.changePassword(customerDTO); } catch (PasswordNotChangedException e) { logger.error("Could not change password PasswordNotChangedException: " + customerDTO.toString()); return "changePassword"; } catch (PasswordNotSecureException e) { return "changePassword"; } return createRedirectViewPath("changePassword"); } Our problem is that when changePassword is invoked the validator ignores the group(PasswordChange.class) and validates only firstName and lastName which are not in the group. Any idea? Thank you very much for your time.

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  • Nested entities in Google App Engine. Do I do it right?

    - by Aleksandr Makov
    Trying to make most of the GAE Datastore entities concept, but some doubts drill my head. Say I have the model: class User(ndb.Model): email = ndb.StringProperty(indexed=True) password = ndb.StringProperty(indexed=False) first_name = ndb.StringProperty(indexed=False) last_name = ndb.StringProperty(indexed=False) created_at = ndb.DateTimeProperty(auto_now_add=True) @classmethod def key(cls, email): return ndb.Key(User, email) @classmethod def Add(cls, email, password, first_name, last_name): user = User(parent=cls.key(email), email=email, password=password, first_name=first_name, last_name=last_name) user.put() UserLogin.Record(email) class UserLogin(ndb.Model): time = ndb.DateTimeProperty(auto_now_add=True) @classmethod def Record(cls, user_email): login = UserLogin(parent=User.key(user_email)) login.put() And I need to keep track of times of successful login operations. Each time user logs in, an UserLogin.Record() method will be executed. Now the question — do I make it right? Thanks. EDIT 2 Ok, used the typed arguments, but then it raised this: Expected Key instance, got User(key=Key('User', 5418393301680128), created_at=datetime.datetime(2013, 6, 27, 10, 12, 25, 479928), email=u'[email protected]', first_name=u'First', last_name=u'Last', password=u'password'). It's clear to understand, but I don't get why the docs are misleading? They implicitly propose to use: # Set Employee as Address entity's parent directly... address = Address(parent=employee) But Model expects key. And what's worse the parent=user.key() swears that key() isn't callable. And I found out the user.key works. EDIT 1 After reading the example form the docs and trying to replicate it — I got type error: TypeError('Model constructor takes no positional arguments.'). This is the exacto code used: user = User('[email protected]', 'password', 'First', 'Last') user.put() stamp = UserLogin(parent=user) stamp.put() I understand that Model was given the wrong argument, BUT why it's in the docs?

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  • Advice for a distracted, unhappy, recently graduated programmer? [closed]

    - by Re-Invent
    I graduated 4 months ago. I had offers from a few good places to work at. At the same time I wanted to stick to building a small software business of my own, still have some ideas with good potential, some half done projects frozen in my github. But due to social pressures, I chose a job, the pay is great, but I am half-passionate about it. A small team of smart folks building useful product, working out contracts across the world. I've started finding it extremely boring. Boring to the extent that I skip 2-3 days a week together not doing work. Neither do I spend that time progressing any of my own projects. Yes, I feel stupid at the way I'm wasting time, but I don't understand exactly why is it happening. It's as if all the excitement has been drained. What can I do about it? Long version: School - I was in third standard. Only students, 6th grade had access to computer labs. I once peeked into the lab from the little door opening. No hard-disks, MS DOS on 5 1/2 inch floppies. I asked a senior student to play some sound in BASIC. He used PLAY to compose a tune. Boy! I was so excited, I was jumping from within. Back home, asked my brother to teach me some programming. We bought a book "MODERN All About GW-BASIC for Schools & Colleges". The book had everything, right from printing, to taking input, file i/o, game programming, machine level support, etc. I was in 6th standard, wrote my first game - a wheel of fortune, rotated the wheel by manipulating 16 color palette's definition. Got internet soon, got hooked to QuickBasic programming community. Made some more games "007 in Danger", "Car Crush 2" for submission to allbasiccode archives. I was extremely excited about all this. My interests now swayed into "hacking" (computer security). Taught myself some perl, found it annoying, learnt PHP and a bit of SQL. Also taught myself Visual Basic one of the winters and wrote a pacman clone with Direct X. By the time I was in 10th standard, I created some evil tools using visual basic, php and mysql and eventually landed myself into an unpaid side-job at a government facility, building evil tools for them. It was a dream come true for crackers of that time. And so was I, still very excited. Things changed soon, last two years of school were not so great as I was balancing preps for college, work at govt. and studies for school at same time. College - College was opposite of all I had wished it to be. I imagined it to be a place where I'd spend my 4 years building something awesome. It was rather an epitome of rote learning, attendance, rules, busy schedules, ban on personal laptops, hardly any hackers surrounding you and shit like that. We had to take permissions to even introduce some cultural/creative activities in our annual schedule. The labs won't be open on weekends because the lab employees had to have their leaves. Yes, a horrible place for someone like me. I still managed to pull out a project with a friend over 2 months. Showed it to people high in the academia hierarchy. They were immensely impressed, we proposed to allow personal computers for students. They made up half-assed reasons and didn't agree. We felt frustrated. And so on, I still managed to teach myself new languages, do new projects of my own, do an intern at the same govt. facility, start a small business for sometime, give a talk at a conference I'm passionate about, win game-dev and hacking contest at most respected colleges, solve good deal of programming contest problems, etc. At the same time I was not content with all these restrictions, great emphasis on rote learning, and sheer wastage of time due to college. I never felt I was overdoing, but now I feel I burnt myself out. During my last days at college, I did an intern at a bigco. While I spent my time building prototypes for certain LBS, the other interns around me, even a good friend, was just skipping time. I thought maybe, in a few weeks he would put in some serious efforts at work assigned to him, but all he did was to find creative ways to skip work, hide his face from manager, engage people in talks if they try to question his progress, etc. I tried a few time to get him on track, but it seems all he wanted was to "not to work hard at all and still reap the fruits". I don't know how others take such people, but I find their vicinity very very poisonous to one's own motivation and productivity. Over that, the place where I come from, HRs don't give much value to what have you done past 4 years. So towards the end of out intern, we all were offered work at the bigco, but the slacker, even after not writing more than 200 lines of code was made a much better offer. I felt enraged instantly - "Is this how the corp world treats someone who does fruitful, if not extra-ordinary work form them for past 6 months?". Yes, I did try to negotiate and debate. The bigcos seem blind due to departmentalization of responsibilities and many layers of management. I decided not to be in touch with any characters of that depressing play. Probably the busy time I had at college, ignoring friends, ignoring fun and squeezing every bit of free time for myself is also responsible. Probably this is what has drained all my willingness to work for anyone. I find my day job boring, at the same time I with to maintain it for financial reasons. I feel a bit burnt out, unsatisfied and at the same time an urge to quit working for someone else and start finishing my frozen side-projects (which may be profitable). Though I haven't got much to support myself with food, office, internet bills, etc in savings. I still have my day job, but I don't find it very interesting, even though the pay is higher than the slacker, I don't find money to be a great motivator here. I keep comparing myself to my past version. I wonder how to get rid of this and reboot myself back to the way I was in school days - excited about it, tinkering, building, learning new things daily, and NOT BORED?

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  • Is nesting types considered bad practice?

    - by Rob Z
    As noted by the title, is nesting types (e.g. enumerated types or structures in a class) considered bad practice or not? When you run Code Analysis in Visual Studio it returns the following message which implies it is: Warning 34 CA1034 : Microsoft.Design : Do not nest type 'ClassName.StructueName'. Alternatively, change its accessibility so that it is not externally visible. However, when I follow the recommendation of the Code Analysis I find that there tend to be a lot of structures and enumerated types floating around in the application that might only apply to a single class or would only be used with that class. As such, would it be appropriate to nest the type sin that case, or is there a better way of doing it?

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  • How to estimate freight / shipping costs ??

    - by Vani
    Hi, I am working on a PHP web application and want to know the best way to estimate freight costs in USA. The site deals with construction materials that uses LTL or Truck loads. I found a few sites like www.freightCenter.com that provide quotes using webservice. Two drawbacks, its paid service and the other, my site response time is slow if I use the webservice. Is there a open source tool/logic avaliable for estimating shipping / freight costs?? Or a way to determine the rate per mile per pound for different freight classes? Thank you, Vani

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  • Decorator not calling the decorated instance - alternative design needed

    - by Daniel Hilgarth
    Assume I have a simple interface for translating text (sample code in C#): public interface ITranslationService { string GetTranslation(string key, CultureInfo targetLanguage); // some other methods... } A first simple implementation of this interface already exists and simply goes to the database for every method call. Assuming a UI that is being translated at start up this results in one database call per control. To improve this, I want to add the following behavior: As soon as a request for one language comes in, fetch all translations from this language and cache them. All translation requests are served from the cache. I thought about implementing this new behavior as a decorator, because all other methods of that interface implemented by the decorater would simple delegate to the decorated instance. However, the implementation of GetTranslation wouldn't use GetTranslation of the decorated instance at all to get all translations of a certain language. It would fire its own query against the database. This breaks the decorator pattern, because every functionality provided by the decorated instance is simply skipped. This becomes a real problem if there are other decorators involved. My understanding is that a Decorator should be additive. In this case however, the decorator is replacing the behavior of the decorated instance. I can't really think of a nice solution for this - how would you solve it? Everything is allowed, even a complete re-design of ITranslationService itself.

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  • How to determine the source of a request in a distributed service system?

    - by Kabumbus
    Map/Reduce is a great concept for sorting large quantities of data at once. What to do if you have small parts of data and you need to reduce it all the time? Simple example - choosing a service for request. Imagine we have 10 services. Each provides services host with sets of request headers and post/get arguments. Each service declares it has 30 unique keys - 10 per set. service A: name id ... Now imagine we have a distributed services host. We have 200 machines with 10 services on each. Each service has 30 unique keys in there sets. but now to find to which service to map the incoming request we make our services post unique values that map to that sets. We can have up to or more than 10 000 such values sets on each machine per each service. service A machine 1 name = Sam id = 13245 ... service A machine 1 name = Ben id = 33232 ... ... service A machine 100 name = Ron id = 777888 ... So we get 200 * 10 * 30 * 30 * 10 000 == 18 000 000 000 and we get 500 requests per second on our gateway each containing 45 items 15 of which are just noise. And our task is to find a service for request (at least a machine it is running on). On all machines all over cluster for same services we have same rules. We can first select to which service came our request via rules filter 10 * 30. and we will have 200 * 30 * 10 000 == 60 000 000. So... 60 mil is definitely a problem... I hope to get on idea of mapping 30 * 10 000 onto some artificial neural network alike Perceptron that outputs 1 if 30 words (some hashes from words) from the request are correct or if less than Perceptron should return 0. And I’ll send each such Perceptron for each service from each machine to gateway. So I would have a map Perceptron <-> machine for each service. Can any one tall me if my Perceptron idea is at least “sane”? Or normal people do it some other way? Or if there are better ANNs for such purposes?

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  • Programming methodologies at stackoverflow

    - by Prototype Stark
    I am in the middle of starting up a software company where we would use ASP.NET MVC and ASP.NET WebAPI extensively at shop. We will be a group of 4 and no more than 10 will work on any particular project at any point in time(these are ground rules). I would like to know, what programming methodologies best suit a small(guerilla) team. Specifically, I would also like to know which ones are being used at famous ASP.NET MVC shops like Stackoverflow. The ones I know are: Scrum and Waterfall(I know its bad). But what's the recommended way of development for smaller, group of 9-10 team. Also, will Test Driven Development help such a team in producing quality software? Are there any other techniques the team will have to know to be good at producing quality software?

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  • Searching integer sequences

    - by David Gibson
    I have a fairly complex search problem that I've managed to reduce to the following description. I've been googling but haven't been able to find an algorithm that seems to fit my problem cleanly. In particular the need to skip arbitrary integers. Maybe someone here can point me to something? Take a sequence of integers A, for example (1 2 3 4) Take various sequences of integers and test if any of them match A such that. A contains all of the integers in the tested sequence The ordering of the integers in the tested sequence are the same in A We don't care about any integers in A that are not in the test sequence We want all matching test sequences, not just the first. An example A = (1 2 3 4) B = (1 3) C = (1 3 4) D = (3 1) E = (1 2 5) B matches A C matches A D does not match A as the ordering is different E does not match A as it contains an integer not in A I hope that this explanation is clear enough. The best I've managed to do is to contruct a tree of the test sequences and iterate over A. The need to be able to skip integers leads to a lot of unsuccessful search paths. Thanks Reading some suggestions I feel that I have to clarify a couple of points that I left too vague. Repeated numbers are allowed, in fact this is quite important as it allows a single test sequence to match A is multiple ways A = (1234356), B = (236), matches could be either -23---6 or -2--3-6 I expect there to be a very large number of test sequences, in the thousands at least and sequence A will tend to have a max length of maybe 20. Thus simply trying to match each test sequence one by one by iterating becomes extremely inefficient. Sorry if this wasn't clear.

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  • Switch or a Dictionary when assigning to new object

    - by KChaloux
    Recently, I've come to prefer mapping 1-1 relationships using Dictionaries instead of Switch statements. I find it to be a little faster to write and easier to mentally process. Unfortunately, when mapping to a new instance of an object, I don't want to define it like this: var fooDict = new Dictionary<int, IBigObject>() { { 0, new Foo() }, // Creates an instance of Foo { 1, new Bar() }, // Creates an instance of Bar { 2, new Baz() } // Creates an instance of Baz } var quux = fooDict[0]; // quux references Foo Given that construct, I've wasted CPU cycles and memory creating 3 objects, doing whatever their constructors might contain, and only ended up using one of them. I also believe that mapping other objects to fooDict[0] in this case will cause them to reference the same thing, rather than creating a new instance of Foo as intended. A solution would be to use a lambda instead: var fooDict = new Dictionary<int, Func<IBigObject>>() { { 0, () => new Foo() }, // Returns a new instance of Foo when invoked { 1, () => new Bar() }, // Ditto Bar { 2, () => new Baz() } // Ditto Baz } var quux = fooDict[0](); // equivalent to saying 'var quux = new Foo();' Is this getting to a point where it's too confusing? It's easy to miss that () on the end. Or is mapping to a function/expression a fairly common practice? The alternative would be to use a switch: IBigObject quux; switch(someInt) { case 0: quux = new Foo(); break; case 1: quux = new Bar(); break; case 2: quux = new Baz(); break; } Which invocation is more acceptable? Dictionary, for faster lookups and fewer keywords (case and break) Switch: More commonly found in code, doesn't require the use of a Func< object for indirection.

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  • When does implementing MVVM not make sense

    - by Kelly Sommers
    I am a big fan of various patterns and enjoy learning new ones all the time however I think with all the evangelism around popular patterns and anti-patterns sometimes this causes blind adoption. I think most things have individual pros and cons and it's important to educate what the cons are and when it doesn't make sense to make a particular choice. The pros are constantly advocated. "It depends" I think applies most times but the industry does a poor job at communicating what it depends ON. Also many patterns surfaced from inheriting values from previous patterns or have derivatives, which each one brings another set of pros and cons to the table. The sooner we are more aware of the trade off's of decisions we make in software architecture the sooner we make better decisions. This is my first challenge to the community. Even if you are a big fan of said pattern, I challenge you to discover the cons and when you shouldn't use it. Define when MVVM (Model-View-ViewModel) may not make sense in a particular piece of software and based on what reasons. MVVM has a set of pros and cons. Let's try to define them. GO! :)

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  • Any enlightenment for understanding Object Oriented Programming? [closed]

    - by ????
    I studied computer science near the end of 1980s, and wasn't taught OOP that formally. With Pascal or C, when I understand the top-down design of functions, and the idea of black box, then everything just seem to make sense, as if there is a "oh I get it!" -- some kind of totally getting it and enlightenment feeling. But with OOP, all I know was the mechanics: the class, instance, method, inheritance, polymorphism, encapsulation. It was like, I knew all the "this is how it is", but never had the feeling of "I totally get it", the enlightened feeling. Would somebody be able to describe it, or point to a chapter in some book or paper which talks about OOP so that the reader can feel: "I totally get it!" on OOP?

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