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• Is software development an engineering discipline?

  - by Vaibhav Garg

  Can software development be considered engineering? If no, what are the things that it lacks in order to be qualified as an engineering discipline? Related to this is this question on Stack Overflow about the difference between a programmer and a software engineer. There is the Software Engineering Institute at Carnigie Mellon University that prescribes and maintains the CMMI standards. Is this something that will turn development into engineering?

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• Ways to ensure unique instances of a class?

  - by Peanut

  I'm looking for different ways to ensure that each instance of a given class is a uniquely identifiable instance. For example, I have a Name class with the field name. Once I have a Name object with name initialised to John Smith I don't want to be able to instantiate a different Name object also with the name as John Smith, or if instantiation does take place I want a reference to the orginal object to be passed back rather than a new object. I'm aware that one way of doing this is to have a static factory that holds a Map of all the current Name objects and the factory checks that an object with John Smith as the name doesn't already exist before passing back a reference to a Name object. Another way I could think of off the top of my head is having a static Map in the Name class and when the constructor is called throwing an exception if the value passed in for name is already in use in another object, however I'm aware throwing exceptions in a constructor is generally a bad idea. Are there other ways of achieving this?

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• What are the best resources for learning about concurrency and multi-threaded applications?

  - by Zepee

  I realised I have a massive knowledge gap when it comes to multi-threaded applications and concurrent programming. I've covered some basics in the past, but most of it seems to be gone from my mind, and it is definitely a field that I want, and need, to be more knowledgeable about. What are the best resources for learning about building concurrent applications? I'm a very practical oriented person, so if said book contains concrete examples the better, but I'm open to suggestions. I personally prefer to work in pseudocode or C++, and a slant toward game development would be best, but not required.

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• Is Debug.Assert obsolete if you write unit tests?

  - by Justin Pihony

  Just like the question asks, is there a need to add Debug.Assert into your code if you are writing unit tests (which has its own assertions)? I could see that this might make the code more obvious without having to go into the tests, however it just seems that you might end up with duplicated asserts. It seems to me that Debug.Assert was helpful before unit-testing became more prevalent, but is now unnecessary. Or, am I not thinking of some use case?

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• Roo gem .xlsx files performance problems [closed]

  - by alvaritogf

  I am getting unacceptable performace problems by using the roo gem for reading a file by using XLSX or XLS library from this gem. Someone may suggest me an alternative about how to parse an .XLSX file? parsed_file = Excel.new(filename,false, :ignore) if (file_format.upcase == "XLS") parsed_file = Excelx.new(filename,false, :ignore) if (file_format.upcase == "XLSX") raise t "#{filename} is not an Excel file!" if (!parsed_file) parsed_file.default_sheet = parsed_file.sheets[0]#'Sheet2'#oo.sheets[1] first_row = parsed_file.first_row last_row = parsed_file.last_row first_column = parsed_file.first_column last_column = parsed_file.last_column #logger.info "#### Total Rows:#{last_row}, first_row:#{first_row}, last_row:#{last_row}, first_column:#{first_column}, last_column:#{last_column}" first_row.upto(last_row) do |current_line| # Stuff .... end Thanks

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• Best Books of C

  - by Patrick

  Hi, I realy want to get high skills in C programming and I know that the best and only way is hard work and lots of practice. though I found so many tutorials and books available on the net about learning the C language. I'm just looking for one or two good books in C that I can learn from and get high skills in C. Anyone knows such a great book/books for C programming pls? (sorry for replication if the question exists already in the forum) Regards!

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• Is it wise to store a big lump of json on a database row

  - by Ieyasu Sawada

  I have this project which stores product details from amazon into the database. Just to give you an idea on how big it is: [{"title":"Genetic Engineering (Opposing Viewpoints)","short_title":"Genetic Engineering ...","brand":"","condition":"","sales_rank":"7171426","binding":"Book","item_detail_url":"http://localhost/wordpress/product/?asin=0737705124","node_list":"Books > Science & Math > Biological Sciences > Biotechnology","node_category":"Books","subcat":"","model_number":"","item_url":"http://localhost/wordpress/wp-content/ecom-plugin-redirects/ecom_redirector.php?id=128","details_url":"http://localhost/wordpress/product/?asin=0737705124","large_image":"http://localhost/wordpress/wp-content/plugins/ecom/img/large-notfound.png","medium_image":"http://localhost/wordpress/wp-content/plugins/ecom/img/medium-notfound.png","small_image":"http://localhost/wordpress/wp-content/plugins/ecom/img/small-notfound.png","thumbnail_image":"http://localhost/wordpress/wp-content/plugins/ecom/img/thumbnail-notfound.png","tiny_img":"http://localhost/wordpress/wp-content/plugins/ecom/img/tiny-notfound.png","swatch_img":"http://localhost/wordpress/wp-content/plugins/ecom/img/swatch-notfound.png","total_images":"6","amount":"33.70","currency":"$","long_currency":"USD","price":"$33.70","price_type":"List Price","show_price_type":"0","stars_url":"","product_review":"","rating":"","yellow_star_class":"","white_star_class":"","rating_text":" of 5","reviews_url":"","review_label":"","reviews_label":"Read all ","review_count":"","create_review_url":"http://localhost/wordpress/wp-content/ecom-plugin-redirects/ecom_redirector.php?id=132","create_review_label":"Write a review","buy_url":"http://localhost/wordpress/wp-content/ecom-plugin-redirects/ecom_redirector.php?id=19186","add_to_cart_action":"http://localhost/wordpress/wp-content/ecom-plugin-redirects/add_to_cart.php","asin":"0737705124","status":"Only 7 left in stock.","snippet_condition":"in_stock","status_class":"ninstck","customer_images":["http://localhost/wordpress/wp-content/uploads/2013/10/ecom_images/51M2vvFvs2BL.jpg","http://localhost/wordpress/wp-content/uploads/2013/10/ecom_images/31FIM-YIUrL.jpg","http://localhost/wordpress/wp-content/uploads/2013/10/ecom_images/51M2vvFvs2BL.jpg","http://localhost/wordpress/wp-content/uploads/2013/10/ecom_images/51M2vvFvs2BL.jpg"],"disclaimer":"","item_attributes":[{"attr":"Author","value":"Greenhaven Press"},{"attr":"Binding","value":"Hardcover"},{"attr":"EAN","value":"9780737705126"},{"attr":"Edition","value":"1"},{"attr":"ISBN","value":"0737705124"},{"attr":"Label","value":"Greenhaven Press"},{"attr":"Manufacturer","value":"Greenhaven Press"},{"attr":"NumberOfItems","value":"1"},{"attr":"NumberOfPages","value":"224"},{"attr":"ProductGroup","value":"Book"},{"attr":"ProductTypeName","value":"ABIS_BOOK"},{"attr":"PublicationDate","value":"2000-06"},{"attr":"Publisher","value":"Greenhaven Press"},{"attr":"SKU","value":"G0737705124I2N00"},{"attr":"Studio","value":"Greenhaven Press"},{"attr":"Title","value":"Genetic Engineering (Opposing Viewpoints)"}],"customer_review_url":"http://localhost/wordpress/wp-content/ecom-customer-reviews/0737705124.html","flickr_results":["http://localhost/wordpress/wp-content/uploads/2013/10/ecom_images/5105560852_06c7d06f14_m.jpg"],"freebase_text":"No around the web data available yet","freebase_image":"http://localhost/wordpress/wp-content/plugins/ecom/img/freebase-notfound.jpg","ebay_related_items":[{"title":"Genetic Engineering (Introducing Issues With Opposing Viewpoints), , Good Book","image":"http://localhost/wordpress/wp-content/uploads/2013/10/ecom_images/140.jpg","url":"http://localhost/wordpress/wp-content/ecom-plugin-redirects/ecom_redirector.php?id=12165","currency_id":"$","current_price":"26.2"},{"title":"Genetic Engineering Opposing Viewpoints by DAVID BENDER - 1964 Hardcover","image":"http://localhost/wordpress/wp-content/uploads/2013/10/ecom_images/140.jpg","url":"http://localhost/wordpress/wp-content/ecom-plugin-redirects/ecom_redirector.php?id=130","currency_id":"AUD","current_price":"11.99"}],"no_follow":"rel=\"nofollow\"","new_tab":"target=\"_blank\"","related_products":[],"super_saver_shipping":"","shipping_availability":"","total_offers":"7","added_to_cart":""}] So the structure for the table is: asin title details (the product details in json) Will the performance suffer if I have to store like 10,000 products? Is there any other way of doing this? I'm thinking of the following, but the current setup is really the most convenient one since I also have to use the data on the client side: store the product details in a file. So something like ASIN123.json store the product details in one big file. (I'm guessing it will be a drag to extract data from this file) store each of the fields in the details in its own table field Thanks in advance!

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• Do you develop with security in mind?

  - by MattyD

  I was listening to a podcast on Security Now and they mentioned about how a lot of the of the security problems found in Flash were because when flash was first developed it wasdn't built with security in mind because it didn't need to thus flash has major security flaws in its design etc. I know best practices state that you should build secure first etc. Some people or companies don't always follow 'best practice'... My question is do you develop to be secure or do you build with all the desired functionality etc then alter the code to be secure (Whatever the project maybe) (I realise that this question could be a possible duplicate of Do you actively think about security when coding? but it is different in the fact of actually process of building the software/application and design of said software/application)

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• How do you keep code with continuations/callbacks readable?

  - by Heinzi

  Summary: Are there some well-established best-practice patterns that I can follow to keep my code readable in spite of using asynchronous code and callbacks? I'm using a JavaScript library that does a lot of stuff asynchronously and heavily relies on callbacks. It seems that writing a simple "load A, load B, ..." method becomes quite complicated and hard to follow using this pattern. Let me give a (contrived) example. Let's say I want to load a bunch of images (asynchronously) from a remote web server. In C#/async, I'd write something like this: disableStartButton(); foreach (myData in myRepository) { var result = await LoadImageAsync("http://my/server/GetImage?" + myData.Id); if (result.Success) { myData.Image = result.Data; } else { write("error loading Image " + myData.Id); return; } } write("success"); enableStartButton(); The code layout follows the "flow of events": First, the start button is disabled, then the images are loaded (await ensures that the UI stays responsive) and then the start button is enabled again. In JavaScript, using callbacks, I came up with this: disableStartButton(); var count = myRepository.length; function loadImage(i) { if (i >= count) { write("success"); enableStartButton(); return; } myData = myRepository[i]; LoadImageAsync("http://my/server/GetImage?" + myData.Id, function(success, data) { if (success) { myData.Image = data; } else { write("error loading image " + myData.Id); return; } loadImage(i+1); } ); } loadImage(0); I think the drawbacks are obvious: I had to rework the loop into a recursive call, the code that's supposed to be executed in the end is somewhere in the middle of the function, the code starting the download (loadImage(0)) is at the very bottom, and it's generally much harder to read and follow. It's ugly and I don't like it. I'm sure that I'm not the first one to encounter this problem, so my question is: Are there some well-established best-practice patterns that I can follow to keep my code readable in spite of using asynchronous code and callbacks?

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• How to name an subclass that add a minor, detailed thing?

  - by Louis Rhys

  What is the most concise (yet descriptive) way of naming a subclass that only add a specific minor thing to the parent? I encountered this case a lot in WPF, where sometime I have to add a small functionality to an out-of-the-box control for specific cases. Example: TreeView doesn't change the SelectedItem on right-click, but I have to make one that does in my application. Some possible names are TreeViewThatChangesSelectedItemOnRightClick (way too wordy and maybe difficult to read because there is so many words concantenated together) TreeView_SelectedItemChangesOnRightClick (slightly more readable, but still too wordy and the underscore also breaks the normal convention for class names) TreeViewThatChangesSIOnRC (non-obvious acronym), ExtendedTreeView (more concise, but doesn't describe what it is doing. Besides, I already found a class called this in the library, that I don't want to use/modify in my application). LouisTreeView, MyTreeView, etc. (doesn't describe what it is doing). It seems that I can't find a name which sounds right. What do you do in situation like this?

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• Formalizing a requirements spec written in narrative English

  - by ProfK

  I have a fairly technical functionality requirements spec, expressed in English prose, produced by my project manager. It is structured as a collection of UI tabs, where the requirements for each tab are expressed as a lit of UI fields and a list of business rules for the tab. Most business rules are for UI fields on a tab, e.g: a) Must be alphanumeric, max length 20. b) Must be a dropdown, with values from table x. c) Is mandatory. d) Is mandatory under certain conditions, e.g. another field is just populated, or has a specific value. Then other business rules get a little more complex. The spec is for a job application, so the central business object (table) is the Applicant, and we have several other tables with one-to-many relationships with applicant, such as Degree, HighSchool, PreviousEmployer, Diploma, etc. e) One such complex rule says a status field can only be assigned a certain value if a many-side record exists in at least one of the many-side tables. E.g. the Applicant has at least one HighSchool or at least one Diploma record. I am looking for advice on how to codify these requirements into a more structured specification defined in terms of tables, fields, and relationships, especially for the conditional rules for fields and for the presence of related records. Any suggestions and advice will be most welcome, but I would be overjoyed if i could find an already defined system or structure for expressing things like this.

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• Merge sort versus quick sort performance

  - by Giorgio

  I have implemented merge sort and quick sort using C (GCC 4.4.3 on Ubuntu 10.04 running on a 4 GB RAM laptop with an Intel DUO CPU at 2GHz) and I wanted to compare the performance of the two algorithms. The prototypes of the sorting functions are: void merge_sort(const char **lines, int start, int end); void quick_sort(const char **lines, int start, int end); i.e. both take an array of pointers to strings and sort the elements with index i : start <= i <= end. I have produced some files containing random strings with length on average 4.5 characters. The test files range from 100 lines to 10000000 lines. I was a bit surprised by the results because, even though I know that merge sort has complexity O(n log(n)) while quick sort is O(n^2), I have often read that on average quick sort should be as fast as merge sort. However, my results are the following. Up to 10000 strings, both algorithms perform equally well. For 10000 strings, both require about 0.007 seconds. For 100000 strings, merge sort is slightly faster with 0.095 s against 0.121 s. For 1000000 strings merge sort takes 1.287 s against 5.233 s of quick sort. For 5000000 strings merge sort takes 7.582 s against 118.240 s of quick sort. For 10000000 strings merge sort takes 16.305 s against 1202.918 s of quick sort. So my question is: are my results as expected, meaning that quick sort is comparable in speed to merge sort for small inputs but, as the size of the input data grows, the fact that its complexity is quadratic will become evident? Here is a sketch of what I did. In the merge sort implementation, the partitioning consists in calling merge sort recursively, i.e. merge_sort(lines, start, (start + end) / 2); merge_sort(lines, 1 + (start + end) / 2, end); Merging of the two sorted sub-array is performed by reading the data from the array lines and writing it to a global temporary array of pointers (this global array is allocate only once). After each merge the pointers are copied back to the original array. So the strings are stored once but I need twice as much memory for the pointers. For quick sort, the partition function chooses the last element of the array to sort as the pivot and scans the previous elements in one loop. After it has produced a partition of the type start ... {elements <= pivot} ... pivotIndex ... {elements > pivot} ... end it calls itself recursively: quick_sort(lines, start, pivotIndex - 1); quick_sort(lines, pivotIndex + 1, end); Note that this quick sort implementation sorts the array in-place and does not require additional memory, therefore it is more memory efficient than the merge sort implementation. So my question is: is there a better way to implement quick sort that is worthwhile trying out? If I improve the quick sort implementation and perform more tests on different data sets (computing the average of the running times on different data sets) can I expect a better performance of quick sort wrt merge sort? EDIT Thank you for your answers. My implementation is in-place and is based on the pseudo-code I have found on wikipedia in Section In-place version: function partition(array, 'left', 'right', 'pivotIndex') where I choose the last element in the range to be sorted as a pivot, i.e. pivotIndex := right. I have checked the code over and over again and it seems correct to me. In order to rule out the case that I am using the wrong implementation I have uploaded the source code on github (in case you would like to take a look at it). Your answers seem to suggest that I am using the wrong test data. I will look into it and try out different test data sets. I will report as soon as I have some results.

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• Ongoing confusion about ivars and properties in objective C

  - by Earl Grey

  After almost 8 months being in ios programming, I am again confused about the right approach. Maybe it is not the language but some OOP principle I am confused about. I don't know.. I was trying C# a few years back. There were fields (private variables, private data in an object), there were getters and setters (methods which exposed something to the world) ,and properties which was THE exposed thing. I liked the elegance of the solution, for example there could be a class that would have a property called DailyRevenue...a float...but there was no private variable called dailyRevenue, there was only a field - an array of single transaction revenues...and the getter for DailyRevenue property calculated the revenue transparently. If somehow the internals of daily revenue calculation would change, it would not affect somebody who consumed my DailyRevenue property in any way, since he would be shielded from getter implementation. I understood that sometimes there was , and sometimes there wasn't a 1-1 relationship between fields and properties. depending on the requirements. It seemed ok in my opinion. And that properties are THE way to acces the data in object. I know the difference betweeen private, protected, and public keyword. Now lets get to objectiveC. On what factor should I base my decision about making someting only an ivar or making it as a property? Is the mental model the same as I describe above? I know that ivars are "protected" by default, not "private" asi in c#..But thats ok I think, no big deal for my presnet level of understanding the whole ios development. The point is ivars are not accesible from outside (given i don't make them public..but i won't). The thing that clouds my clear understanding is that I can have IBOutlets from ivars. Why am I seeing internal object data in the UI? *Why is it ok?* On the other hand, if I make an IBOutlet from property, and I do not make it readonly, anybody can change it. Is this ok too? Let's say I have a ParseManager object. This object would use a built in Foundation framework class called NSXMLParser. Obviously my ParseManager will utilize this nsxmlparser's capabilities but will also do some additional work. Now my question is, who should initialize this NSXMLParser object and in which way should I make a reference to it from the ParseManager object, when there is a need to parse something. A) the ParseManager -1) in its default init method (possible here ivar - or - ivar+ppty) -2) with lazyloading in getter (required a ppty here) B) Some other object - who will pass a reference to NSXMLParser object to the ParseManager object. -1) in some custom initializer (initWithParser:(NSXMLPArser *) parser) when creating the ParseManager object.. A1 - the problem is, we create a parser and waste memory while it is not yet needed. However, we can be sure that all methods that are part ot ParserManager object, can use the ivar safely, since it exists. A2 - the problem is, the nsxmlparser is exposed to outside world, although it could be read only. Would we want a parser to be exposed in some scenario? B1 - this could maybe be useful when we would want to use more types of parsers..i dont know... I understand that architectural requirements and and language is not the same. But clearly the two are in relation. How to get out of that mess of my? Please bear with me, I wasn't able to come up with a single ultimate question. And secondly, it's better to not scare me with some superadvanced newspeak that talks about some crazy internals (what the compiler does) and edge cases.

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• Task ownership with Wordpress - CSS - Designer or Developer?

  - by Syed Absar

  We have a dispute regarding who owns which tasks when it comes to the CSS on our live site. Our designer argues that he is not responsible to log-in to word press and modify the css or use ftp for any changes because that's not his job description while developer argues that since it is css, it belongs to designer and that he is to update the changes to the server and then compare and correct the output. I'd like experienced people working in professional development environment to put a light on this scenario. I'm not sure if this is the right place to ask this question, or is there a separate forum for business development or project management specific questions?

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• Is it reasonable to expect knowing the whole stack bottom up?

  - by Vaibhav Garg

  I am an Sr. developer/architect/Product Manager for embedded systems. The systems that I have had experience with have typically been small to medium size codebases - typically close to 25-30K LOC in C, using 8-16 and 32 bit low end microcontrollers. The systems have been entirely bootstrapped by our team - meaning right from the start-up code to the end application code has either been written by the team, or at the very least, is thoroughly understood and maintained by us. Now, if we were to start developing more complex systems with complex peripherals, such as USB OTG et al. (think, low end cell phones), there are libraries and stacks available commercially and from chip vendors that reduce the task to just calling the right APIs and being able to use those peripherals. Now, from a habit point of view, this does not give me and the team a comfortable feeling, not being able to comprehend the entire code tree, with virtual black boxes at the lower layers. Is it reasonable to devote, and reserve, time getting into the details of how the APIs are implemented, assuming that the same would also entail getting into details of relevant standards (again, for USB as an example)? Or, alternatively, should a thorough understanding of the top level usage of the APIs be sufficient? This of course assumes that the source codes to all libraries are available, which they are, in almost all cases. Edit: In partial response to @Abhi Beckert, the documentation is refreshingly very comprehensive and meticulously maintained, AFAIK and been able to judge. I have not had a long experience with the same.

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• Is it necessary to read every single byte to check if a copied file is identical to the original?

  - by Koen027

  I recently learned of a program called Total Commander. It's a Windows Explorer replacement and has its own stuff to copy files. To check whether the files are identical, instead of calculation a CRC, it literally checks every single byte, one at a time, on both the original and the copy. My question is: Is this necessary? Can CRC or any other such technique go wrong? Should you, as a programmer, try and implement this perfect but slow system, or is it too extreme?

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• Strategies for browser compatibility on web applications in a corporate environment

  - by TiagoBrenck

  With the new CSS 3 and HTML 5 technology, web applications have gained a lot of new tools for a better UI (user interface) interaction, beautiful templates and even responsive layout to fit into tablets and smartphones. Within a corporate environment, those new technologies are required so the company can "follow" the IT evolution and their concurrent, but they also want that those new web applications supports old browsers. How should I deal with this situation? By one side we are asked to follow the the evolution of technology, create responsive layouts and use a lot of cool jQuery plugins. On the other hand, we are asked to support old browsers that do not support those new responsive features, plugins or components. I would like advice and strategies on how to create "modern" web applications that are also supported on old browsers. How does your company deal with this situation? Is it possible to have the same web application run well and beautifully on old browsers, and be responsive and interactive on newer browsers?

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• Is there an established convention for separating Windows file names in a string?

  - by Heinzi

  I have a function which needs to output a string containing a list of file paths. I can choose the separation character but I cannot change the data type (e.g. I cannot return a List<string> or something like that). Wanting to use some well-established convention, my first intuition was to use the semicolon, similar to what Windows's PATH and Java's CLASSPATH (on Windows) environment variables do: C:\somedir\somefile.txt;C:\someotherdir\someotherfile.txt However, I was surprised to notice that ; is a valid character in an NTFS file name. So, is the established best practice to just ignore this fact (i.e. "no sane person should use ; in a file name and if they do, it's their own fault") or is there some other established character for separating Windows paths or files? (The pipe (|) might be a good choice, but I have not seen it used anywhere yet for this purpose.)

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• MVC data binding

  - by user441521

  I'm using MVC but I've read that MVVM is sort of about data binding and having pure markup in your views that data bind back to the backend via the data-* attributes. I've looked at knockout but it looks pretty low level and I feel like I can make a library that does this and is much easier to use where basically you only need to call 1 javascript function that will data bind your entire page because of the data-* attributes you assign to html elements. The benefits of this (that I see) is that your view is 100% decoupled from your back-end so that a given view never has to be changed if your back-end changes (ie for asp.net people no more razor in your view that makes your view specific to MS). My question would be, I know there is knockout out there but are there any others that provide this data binding functionality for MVC type applications? I don't want to recreate something that may already exist but I want to make something "better" and easier to use than knockout. To give an example of what I mean here is all the code one would need to get data binding in my library. This isn't final but just showing the idea that all you have to do is call 1 javascript function and set some data-* attribute values and everything ties together. Is this worth seeing through? <script> $(function () { // this is all you have to call to make databinding for POST or GET to work DataBind(); }); </script> <form id="addCustomer" data-bind="Customer" data-controller="Home" data-action="CreateCustomer"> Name: <input type="text" data-bind="Name" data-bind-type="text" /> Birthday: <input type="text" data-bind="Birthday" data-bind-type="text" /> Address: <input type="text" data-bind="Address" data-bind-type="text" /> <input type="submit" value="Save" id="btnSave" /> </form> ================================================= // controller action [HttpPost] public string CreateCustomer(Customer customer) { if(customer.Name == "Rick") return "success"; return "failure"; } // model public class Customer { public string Name { get; set; } public DateTime Birthday { get; set; } public string Address { get; set; } }

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• A talk about observer pattern

  - by Martin

  As part of a university course I'm taking, I have to hold a 10 minute talk about the observer pattern. So far these are my points: What is it? (defenition) Polling is an alternative Polling VS Observer When Observer is better When Polling is better (taken from here) A statement that Mediator pattern is worth checking out. (I won't have time to cover it in 10 minutes) I would be happy to hear about: Any suggestions to add something? Another alternative (if exists)

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• Project structure: where to put business logic

  - by Mister Smith

  First of all, I'm not asking where does business logic belong. This has been asked before and most answers I've read agree in that it belongs in the model: Where to put business logic in MVC design? How much business logic should be allowed to exist in the controller layer? How accurate is "Business logic should be in a service, not in a model"? Why put the business logic in the model? What happens when I have multiple types of storage? However people disagree in the way this logic should be distributed across classes. There seem to exist three major currents of thought: Fat model with business logic inside entity classes. Anemic model and business logic in "Service" classes. It depends. I find all of them problematic. The first option is what most Fowlerites stick to. The problem with a fat model is that sometimes a business logic funtion is not only related to a class, and instead uses a bunch of other classes. If, for example, we are developing a web store, there should be a function that calcs an order's total. We could think of putting this function inside the Order class, but what actually happens is that the logic needs to use different classes, not only data contained in the Order class, but also in the User class, the Session class, and maybe the Tax class, Country class, or Giftcard, Payment, etc. Some of these classes could be composed inside the Order class, but some others not. Sorry if the example is not very good, but I hope you understand what I mean. Putting such a function inside the Order class would break the single responsibility principle, adding unnecesary dependences. The business logic would be scattered across entity classes, making it hard to find. The second option is the one I usually follow, but after many projects I'm still in doubt about how to name the class or classes holding the business logic. In my company we usually develop apps with offline capabilities. The user is able to perform entire transactions offline, so all validation and business rules should be implemented in the client, and then there's usually a background thread that syncs with the server. So we usually have the following classes/packages in every project: Data model (DTOs) Data Access Layer (Persistence) Web Services layer (Usually one class per WS, and one method per WS method). Now for the business logic, what is the standard approach? A single class holding all the logic? Multiple classes? (if so, what criteria is used to distribute the logic across them?). And how should we name them? FooManager? FooService? (I know the last one is common, but in our case it is bad naming because the WS layer usually has classes named FooWebService). The third option is probably the right one, but it is also devoid of any useful info. To sum up: I don't like the first approach, but I accept that I might have been unable to fully understand the Zen of it. So if you advocate for fat models as the only and universal solution you are welcome to post links explaining how to do it the right way. I'd like to know what is the standard design and naming conventions for the second approach in OO languages. Class names and package structure, in particular. It would also be helpful too if you could include links to Open Source projects showing how it is done. Thanks in advance.

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• scrapy cannot find div on this website [on hold]

  - by Jaspal Singh Rathour

  I am very new at this and have been trying to get my head around my first selector can somebody help? i am trying to extract data from page http://groceries.asda.com/asda-webstore/landing/home.shtml?cmpid=ahc--ghs-d1--asdacom-dsk-_-hp#/shelf/1215337195041/1/so_false all the info under div class = listing clearfix shelfListing but i cant seem to figure out how to format response.xpath(). I have managed to launch scrapy console but no matter what I type in response.xpath() i cant seem to select the right node. I know it works because when I type response.xpath('//div[@class="container"]') I get a response but don't know how to navigate to the listsing cleardix shelflisting. I am hoping that once i get this bit I can continue working my way through the spider. Thank you in advance! PS I wonder if it is not possible to scan this site - is it possible for the owners to block spiders?

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• org.apache.sling.scripting.jsp.jasper.JasperException: Unable to load tag handler class [migrated]

  - by Babak Behzadi

  I'm developing an Apache Sling WCMS and using java tag libs to rendering some data. I defined a jsp tag lib with following descriptor and handler class: TLD file contains: <?xml version="1.0" encoding="UTF-8"?> <taglib version="2.1" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-jsptaglibrary_2_1.xsd"> <tlib-version>1.0</tlib-version> <short-name>taglibdescriptor</short-name> <uri>http://bob/taglibs</uri> <tag> <name>testTag</name> <body-content>tagdependent</body-content> <tag-class>org.bob.taglibs.test.TestTagHandler</tag-class> </tag> </taglib> Tag handler class: package org.bob.taglibs.test; import javax.servlet.jsp.tagext.TagSupport; public class TestTagHandler extends TagSupport{ @Override public int doStartTag(){ try { pageContext.getOut().print("<h1>Helloooooooo</h1>"); } catch(Exception e) { return SKIP_BODY; } return EVAL_BODY_INCLUDE; } } I packaged the tag lib as BobTagLib.jar and deployed it as a bundle using Sling Web Console. I used this tag lib in a jsp page deployed in my Sling repository: index.jsp: <%@ page contentType="text/html;charset=UTF-8" language="java" %> <%@ taglib prefix="bob" uri="http://bob/taglibs" %> <html> <head><title>Simple jsp page</title></head> <body> <bob:testTag/> </body> </html> Calling the page cause the following exception: org.apache.sling.scripting.jsp.jasper.JasperException: /apps/TagTest/index.jsp(7,5) Unable to load tag handler class "org.bob.taglibs.test.TestTagHandler" for tag "bob:testTag" ... Can any one get me a solution? In advance, any help is apreciated.

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• What are algorithmic paradigms?

  - by Vaibhav Agarwal

  We generally talk about paradigms of programming as functional, procedural, object oriented, imperative etc but what should I reply when I am asked the paradigms of algorithms? For example are Travelling Salesman Problem, Dijkstra Shortest Path Algorithm, Euclid GCD Algorithm, Binary search, Kruskal's Minimum Spanning Tree, Tower of Hanoi paradigms of algorithms? Should I answer the data structures I would use to design these algorithms?

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• Is eval the defmacro of javascript?

  - by Florian Margaine

  In Common Lisp, defmacro basically allows us to build our own DSL. I read this page today and it explains something cleverly done: But I wasn't about to write out all these boring predicates myself, so I defined a function that, given a list of words, builds up the text for such a predicate automatically, and then evals it to produce a function. Which just looks like defmacro to me. Is eval the defmacro of javascript? Could it be used as such?

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