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  • Inheritance vs specific types in Financial Modelling for cashflows

    - by BlueTrin
    Hello, I have to program some financial applications where I have to represent a schedule of flows. The flows can be of 3 types: - fee flow (just a lump payment at some date) - floating rate flow (the flow is dependant of an interest rate to be determined at a later date) - fixed rate flow (the flow is dependant of an interest rate determined when the deal is done) I need to keep the whole information and I need to represent a schedule of these flows. Originally I wanted to use inheritance and create three classes FeeFlow, FloatingFlow, FixedFlow all inheriting from ICashFlow and implement some method GetFlowType() returning an enum then I could dynamic_cast the object to the correct type. That would allow me to have only one vector to represent my schedule. What do you think of this design, should I rather use three vectors vector, vector and vector to avoid the dynamic casts ?

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  • Field Members vs Method Variables?

    - by Braveyard
    Recently I've been thinking about performance difference between class field members and method variables. What exactly I mean is in the example below : Lets say we have a DataContext object for Linq2SQL class DataLayer { ProductDataContext context = new ProductDataContext(); public IQueryable<Product> GetData() { return context.Where(t=>t.ProductId == 2); } } In the example above, context will be stored in heap and the GetData method variables will be removed from Stack after Method is executed. So lets examine the following example to make a distinction : class DataLayer { public IQueryable<Product> GetData() { ProductDataContext context = new ProductDataContext(); return context.Where(t=>t.ProductId == 2); } } (*1) So okay first thing we know is if we define ProductDataContext instance as a field, we can reach it everywhere in the class which means we don't have to create same object instance all the time. But lets say we are talking about Asp.NET and once the users press submit button the post data is sent to the server and the events are executed and the posted data stored in a database via the method above so it is probable that the same user can send different data after one another.If I know correctly after the page is executed, the finalizers come into play and clear things from memory (from heap) and that means we lose our instance variables from memory as well and after another post, DataContext should be created once again for the new page cycle. So it seems the only benefit of declaring it publicly to the whole class is the just number one text above. Or is there something other? Thanks in advance... (If I told something incorrect please fix me.. )

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  • Ruby/Rails - Add records to an object with each loop iteration / Object vs Arrays

    - by ChrisWesAllen
    I'm trying to figure out how to add records to an existing object for each iteration of a loop. I'm having a hard time discovering the difference between an object and an array. I have this @events = Event.find(1) @loops = Choices.find(:all, :limit => 5) #so loop for 5 instances of choice model for loop in @loops @events = Event.find(:all,:conditions => ["event.id = ?", loop.event_id ]) end I'm trying to add a new events to the existing @events object based on the id of whatever the loop variable is. But the ( = ) operator just creates a new instance of the @events object. I tried ( += ) and ( << ) as operators but got the error "You have a nil object when you didn't expect it! You might have expected an instance of Array. The error occurred while evaluating nil" I tried created an array events = [] events << Event.find(1) @loops = Choices.find(:all, :limit => 5) #so loop for 5 instances of choice model for loop in @loops events << Event.find(:all,:conditions => ["event.id = ?", loop.event_id ]) end But I dont know how to call that arrays attributes within the view With objects I was able do create a loop within the view and call all the attributes of that object as well... <table> <% for event in @events %> <tr> <td><%= link_to event.title, event %></td> <td><%= event.start_date %></td> <td><%= event.price %></td> </tr> <% end %> </table> How could i do this with an array set? So the questions are 1) Whats the difference between arrays and objects? 2) Is there a way to add into the existing object for each iteration? 3) If I use an array, is there a way to call the attributes for each array record within the view?

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  • Appropriate uses of Monad `fail` vs. MonadPlus `mzero`

    - by jberryman
    This is a question that has come up several times for me in the design code, especially libraries. There seems to be some interest in it so I thought it might make a good community wiki. The fail method in Monad is considered by some to be a wart; a somewhat arbitrary addition to the class that does not come from the original category theory. But of course in the current state of things, many Monad types have logical and useful fail instances. The MonadPlus class is a sub-class of Monad that provides an mzero method which logically encapsulates the idea of failure in a monad. So a library designer who wants to write some monadic code that does some sort of failure handling can choose to make his code use the fail method in Monad or restrict his code to the MonadPlus class, just so that he can feel good about using mzero, even though he doesn't care about the monoidal combining mplus operation at all. Some discussions on this subject are in this wiki page about proposals to reform the MonadPlus class. So I guess I have one specific question: What monad instances, if any, have a natural fail method, but cannot be instances of MonadPlus because they have no logical implementation for mplus? But I'm mostly interested in a discussion about this subject. Thanks! EDIT: One final thought occured to me. I recently learned (even though it's right there in the docs for fail) that monadic "do" notation is desugared in such a way that pattern match failures, as in (x:xs) <- return [] call the monad's fail. It seems like the language designers must have been strongly influenced by the prospect of some automatic failure handling built in to haskell's syntax in their inclusion of fail in Monad.

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  • Stored procedures vs. parameter binding

    - by Gagan
    I am using SQL server and ODBC in visual c++ for writing to the database. Currently i am using parameter binding in SQL queries ( as i fill the database with only 5 - 6 queries and same is true for retrieving data). I dont know much about stored procedures and I am wondering how much if any performance increase stored procedures have over parameter binding as in parameter binding we prepare the query only once and just execute it later in the program for diferent set of values of variables.

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  • Build server polling vs. event-driven builds

    - by Daniel T.
    Why do build servers poll for changes instead of SVN firing off an event (or a post-commit step) that tells the build server to start a build? It seems terribly inefficient to poll for changes, especially when the number of projects increases and the polling period is set to a very low value (for example, 30 seconds).

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  • Chrome vs Safari - CSS the mystery pixel

    - by Aji
    I have an issue of the mysterious pixel in CSS. Site in question: http://www.lymphcareri.com/about/ The idea is that under the menu is a line, which gets highlighted upon hover and blends in with the line under the header. However, Safari and Chrome both interpret the CSS different in such a way, that I cannot get those lines to line up in both browsers (no pun intended). It is either on the mark, or off. Chrome shaves off one pixel on the bottom margin of the nav link, making the line appear just above. Any idea why that is?

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  • <asp:Table> Vs html <table>

    - by keith
    What are the pros and cons between using the ASP.Net control compared to the old reliable table html implementation. I know that the asp:Table will end up on the returned page as a html table, and from looking into it so far people are saying its easier to work with the asp:Table in the server side code, but I'd love to hear what the stackoverflow community has to say about the matter.

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  • Interview Question: .Any() vs if (.Length > 0) for testing if a collection has elements

    - by Chris
    In a recent interview I was asked what the difference between .Any() and .Length > 0 was and why I would use either when testing to see if a collection had elements. This threw me a little as it seems a little obvious but feel I may be missing something. I suggested that you use .Length when you simply need to know that a collection has elements and .Any() when you wish to filter the results. Presumably .Any() takes a performance hit too as it has to do a loop / query internally.

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  • Tellurium vs Selenium : Compare

    - by Rajasankar
    I am using selenium for sometime and doing good with it. I would like to try Tellurium. Searched and find only few questions about that. I would like to know the following What is the main advantages of using Tellurium? How it is different Selenium+Groovy?

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  • Good concurrency example of Java vs. Clojure

    - by Michiel Borkent
    Clojure is said to be a language that makes multi-thread programming easier. From the Clojure.org website: Clojure simplifies multi-threaded programming in several ways. Now I'm looking for a non-trivial problem solved in Java and in Clojure so I can compare/contrast their simplicity. Anyone?

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  • assignment vs std::swap and merging and keeping duplicates in seperate object

    - by rubenvb
    Say I have two std::set<std::string>s. The first one, old_options, needs to be merged with additional options, contained in new_options. I can't just use std::merge (well, I do, but not only that) because I also check for doubles and warn the user about this accordingly. To this effect, I have void merge_options( set<string> &old_options, const set<string> &new_options ) { // find duplicates and create merged_options, a stringset containing the merged options // handle duplicated the way I want to // ... old_options = merged_options; } Is it better to use std::swap( merged_options, old_options ); or the assignment I have? Is there a better way to filter duplicates and return the merged set than consecutive calls to std::set_intersection and std::set_union to detect dupes and merge the sets? I know it's slower than one traversal and doing both at once, but these sets are small (performance is not critical) and I trust the Standard more than I trust myself.

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  • Android Calendar API vs Calendar Provider API

    - by John Roberts
    I'm a little bit confused about the difference between the two. An example of the Calendar API is supposedly located here: http://samples.google-api-java-client.googlecode.com/hg/calendar-android-sample/instructions.html, but the author himself suggests using the Calendar Provider API, details about which are here: http://developer.android.com/guide/topics/providers/calendar-provider.html. Can someone explain to me the difference between the two, and which would be better for me to use for a simple calendar app?

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  • Java: Tracking a user login session - Session EJBs vs HTTPSession

    - by bguiz
    If I want to keep track of a conversational state with each client using my web application, which is the better alternative - a Session Bean or a HTTP Session - to use? Using HTTP Session: //request is a variable of the class javax.servlet.http.HttpServletRequest //UserState is a POJO HttpSession session = request.getSession(true); UserState state = (UserState)(session.getAttribute("UserState")); if (state == null) { //create default value .. } String uid = state.getUID(); //now do things with the user id Using Session EJB: In the implementation of ServletContextListener registered as a Web Application Listener in WEB-INF/web.xml: //UserState NOT a POJO this this time, it is //the interface of the UserStateBean Stateful Session EJB @EJB private UserState userStateBean; public void contextInitialized(ServletContextEvent sce) { ServletContext servletContext = sce.getServletContext(); servletContext.setAttribute("UserState", userStateBean); ... In a JSP: public void jspInit() { UserState state = (UserState)(getServletContext().getAttribute("UserState")); ... } Elsewhere in the body of the same JSP: String uid = state.getUID(); //now do things with the user id It seems to me that the they are almost the same, with the main difference being that the UserState instance is being transported in the HttpRequest.HttpSession in the former, and in a ServletContext in the case of the latter. Which of the two methods is more robust, and why?

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  • self.window.rootViewController vs window addSubview

    - by Gazzer
    I've noticed a lot of examples for iPhone apps in the Application Delegate - (void)applicationDidFinishLaunching:(UIApplication *)application have [window addSubview: someController.view]; (1) as opposed to self.window.rootViewController = self.someController; (2) Is there any practical reason to use one over the other? Is one technically correct? Do controller's have the an equivalent command to number (2) like self.someController.rootController = self.someOtherController; // pseudocode

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  • selenium vs phpunit/lime?

    - by fayer
    i have seen the power of selenium and that it can give you the tests in different languages. so the question is, why should i use phpunit or lime (for symfony) when a solution like selenium is available? isn't it time-consuming to write all the tests by hand, when you can just use selenium? thanks.

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  • Zend Framework Relations vs. Table Select

    - by rtmilker
    Hey! I just want to know your guys opinion on using join tables within the zend framework. Of course you can use relations by defining a referenceMap and dependentTables and stuff, or using setIntegrityCheck(false) within a db select(). The setIntegrityCheck version seems a little bit dirty to me, but the other version is not very suitable for big querys and joining many tables... I'm a PHP developer for 5 years now and new to the zend framework and just want get a direction for my first project. Thanks!!!

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  • Sun webstack vs Installing PHP, MySQL, Apache individually

    - by Vincent
    Is it possible to install PHP, MySQL, Apache individually on Solaris instead of installing them through a webstack? What are the advantages and disadvantages? I seem to frequently get a CURL error on Solaris when dealing with HTTPS sites. (error:81072080:lib(129):func(114):reason(128). I have no clue why that error is occuring and thought it might solve it, if I upgrade to latest PHP,MySQL,Apache versions. At this point I am not even sure if it's a Solaris issue. Any advice? Thanks

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  • align li tags with an auto width vs hard coding

    - by Diver Dan
    I am having trouble trying to get a group of li tags to align how I want. I have some basic html <div class="menu"> <ul> <li>Item 1</li> <li>Item 2</li> <li>Item 3</li> </ul> </div>? and some css .menu { border:solid 2px red; width:520px; } ul { border:solid 1px #e5e5e5; height:40px; margin:0 auto; list-style:none; width:500px; } li{ text-align:center; display:inline; margin:10px; } I dont want to hard code li widths for each of the elements but I would like for the li elements to take up all available space with the ul element. What do I need to change to get the result I am looking for? My attempt on jsfiddle

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  • Proc.new vs Lambda in Ruby

    - by piemesons
    Plese check this: def foo f = Proc.new { return "return from foo from inside proc" } f.call # control leaves foo here return "return from foo" end def bar f = lambda { return "return from lambda" } f.call # control does not leave bar here return "return from bar" end puts foo # prints "return from foo from inside proc" puts bar # prints "return from bar" Can anybody tell me what lambda is and what is Proc and whats the difference.

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  • Stateless singleton VS Static methods

    - by Sebastien Lorber
    Hey, Don't find any good answer to this simple question about helper/utils classes: Why would i create a singleton (stateless) rather than static methods? Why an object instance could be needed while the object has no state? Sometimes i really don't know what to use...

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