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  • Practical rules for premature optimization

    - by DougW
    It seems that the phrase "Premature Optimization" is the buzz-word of the day. For some reason, iphone programmers in particular seem to think of avoiding premature optimization as a pro-active goal, rather than the natural result of simply avoiding distraction. The problem is, the term is beginning to be applied more and more to cases that are completely inappropriate. For example, I've seen a growing number of people say not to worry about the complexity of an algorithm, because that's premature optimization (eg http://stackoverflow.com/questions/2190275/help-sorting-an-nsarray-across-two-properties-with-nssortdescriptor/2191720#2191720). Frankly, I think this is just laziness, and appalling to disciplined computer science. But it has occurred to me that maybe considering the complexity and performance of algorithms is going the way of assembly loop unrolling, and other optimization techniques that are now considered unnecessary. What do you think? Are we at the point now where deciding between an O(n^n) and O(n!) complexity algorithm is irrelevant? What about O(n) vs O(n*n)? What do you consider "premature optimization"? What practical rules do you use to consciously or unconsciously avoid it? This is a bit vague, but I'm curious to hear other peoples' opinions on the topic.

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  • Simplest PHP Routing framework .. ?

    - by David
    I'm looking for the simplest implementation of a routing framework in PHP, in a typical PHP environment (Running on Apache, or maybe nginx) .. It's the implementation itself I'm mostly interested in, and how you'd accomplish it. I'm thinking it should handle URL's, with the minimal rewriting possible, (is it really a good idea, to have the same entrypoint for all dynamic requests?!), and it should not mess with the querystring, so I should still be able to fetch GET params with $_GET['var'] as you'd usually do.. So far I have only come across .htaccess solutions that puts everything through an index.php, which is sort of okay. Not sure if there are other ways of doing it. How would you "attach" what URL's fit to what controllers, and the relation between them? I've seen different styles. One huge array, with regular expressions and other stuff to contain the mapping. The one I think I like the best is where each controller declares what map it has, and thereby, you won't have one huge "global" map, but a lot of small ones, each neatly separated. So you'd have something like: class Root { public $map = array( 'startpage' => 'ControllerStartPage' ); } class ControllerStartPage { public $map = array( 'welcome' => 'WelcomeControllerPage' ); } // Etc ... Where: 'http://myapp/' // maps to the Root class 'http://myapp/startpage' // maps to the ControllerStartPage class 'http://myapp/startpage/welcome' // maps to the WelcomeControllerPage class 'http://myapp/startpage/?hello=world' // Should of course have $_GET['hello'] == 'world' What do you think? Do you use anything yourself, or have any ideas? I'm not interested in huge frameworks already solving this problem, but the smallest possible implementation you could think of. I'm having a hard time coming up with a solution satisfying enough, for my own taste. There must be something pleasing out there that handles a sane bootstrapping process of a PHP application without trying to pull a big magic hat over your head, and force you to use "their way", or the highway! ;)

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  • Is -1 a magic number? An anti-pattern? A code smell? Quotes and guidelines from authorities

    - by polygenelubricants
    I've seen -1 used in various APIs, most commonly when searching into a "collection" with zero-based indices, usually to indicate the "not found" index. This "works" because -1 is never a legal index to begin with. It seems that any negative number should work, but I think -1 is almost always used, as some sort of (unwritten?) convention. I would like to limit the scope to Java at least for now. My questions are: What are the official words from Sun regarding using -1 as a "special" return value like this? What quotes are there regarding this issue, from e.g. James Gosling, Josh Bloch, or even other authoritative figures outside of Java? What were some of the notable discussions regarding this issue in the past?

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  • When should I be cautious using data binding in .NET?

    - by Ben McCormack
    I just started working on a small team of .NET programmers about a month ago and recently got in a discussion with our team lead regarding why we don't use databinding at all in our code. Every time we work with a data grid, we iterate through a data table and populate the grid row by row; the code usually looks something like this: Dim dt as DataTable = FuncLib.GetData("spGetTheData ...") Dim i As Integer For i = 0 To dt.Rows.Length - 1 '(not sure why we do not use a for each here)' gridRow = grid.Rows.Add() gridRow(constantProductID).Value = dt("ProductID").Value gridRow(constantProductDesc).Value = dt("ProductDescription").Value Next '(I am probably missing something in the code, but that is basically it)' Our team lead was saying that he got burned using data binding when working with Sheridan Grid controls, VB6, and ADO recordsets back in the nineties. He's not sure what the exact problem was, but he remembers that binding didn't work as expected and caused him some major problems. Since then, they haven't trusted data binding and load the data for all their controls by hand. The reason the conversation even came up was because I found data binding to be very simple and really liked separating the data presentation (in this case, the data grid) from the in-memory data source (in this case, the data table). "Loading" the data row by row into the grid seemed to break this distinction. I also observed that with the advent of XAML in WPF and Silverlight, data-binding seems like a must-have in order to be able to cleanly wire up a designer's XAML code with your data. When should I be cautious of using data-binding in .NET?

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  • Password reset by email without a database table

    - by jpatokal
    The normal flow for resetting a user's password by mail is this: Generate a random string and store it in a database table Email string to user User clicks on link containing string String is validated against database; if it matches, user's pw is reset However, maintaining a table and expiring old strings etc seems like a bit of an unnecessary hassle. Are there any obvious flaws in this alternative approach? Generate a MD5 hash of the user's existing password Email hash string to user User clicks on link containing string String is validated by hashing existing pw again; if it matches, user's pw is reset Note that the user's password is already stored in a hashed and salted form, and I'm just hashing it once more to get a unique but repeatable string. And yes, there is one obvious "flaw": the reset link thus generated will not expire until the user changes their password (clicks the link). I don't really see why this would be a problem though -- if the mailbox is compromised, the user is screwed anyway.

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  • Best strategy for synching data in iPhone app

    - by iamj4de
    I am working on a regular iPhone app which pulls data from a server (XML, JSON, etc...), and I'm wondering what is the best way to implement synching data. Criteria are speed (less network data exchange), robustness (data recovery in case update fails), offline access and flexibility (adaptable when the structure of the database changes slightly, like a new column). I know it varies from app to app, but can you guys share some of your strategy/experience? For me, I'm thinking of something like this: 1) Store Last Modified Date in iPhone 2) Upon launching, send a message like getNewData.php?lastModifiedDate=... 3) Server will process and send back only modified data from last time. 4) This data is formatted as so: <+><data id="..."></data></+> // add this to SQLite/CoreData <-><data id="..."></data></-> // remove this <%><data id="..."><attribute>newValue</attribute></data></%> // new modified value I don't want to make <+, <-, <%... for each attribute as well, because it would be too complicated, so probably when receive a <% field, I would just remove the data with the specified id and then add it again (assuming id here is not some automatically auto-incremented field). 5) Once everything is downloaded and updated, I will update the Last Modified Date field. The main problem with this strategy is: If the network goes down when I am updating something = the Last Modified Date is not yet updated = next time I relaunch the app, I will have to go through the same thing again. Not to mention potential inconsistent data. If I use a temporary table for update and make the whole thing atomic, it would work, but then again, if the update is too long (lots of data change), the user has to wait a long time until new data is available. Should I use Last-Modified-Date for each of the data field and update data gradually?

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  • Another answer to the CAPTCHA problem?

    - by Xeoncross
    Most sites at least employ server access log checking and banning along with some kind of bot prevention measure like a CAPTCHA (those messed-up text images). The problem with CAPTCHAs is that they poss a threat to the user experience. Luckily they now come with user friendly features like refresh and audio versions. Anyway, like linux vs windows, it isn't worth the time of a spammer to customize and/or build a script to handle a custom CAPTCHA example that only pertains to one site. Therefore, I was wondering if there might be better ways to handle the whole CAPTCHA thing. In A Better CAPTCHA Peter Bromberg mentions that one way would be to convert the image to HTML and display it embedded in the page. On http://shiflett.org/ Chris simply asks users to type his name into an input. Examples like this are ways to simplifying the CAPTCHA experience while decreasing the value for spammers. Does anyone know of more good examples I could use or see any problem with the embedded image idea?

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  • Should ActionResult perform other tasks too

    - by Ori
    In Asp.net MVC one is encouraged to derive custom ActionResults, however should these classes handle other tasks unrelated to views, perhaps a EmailActionResult would render a view then send an email. What is best practice for the class ActionResult, is it only view specific? I want to keep things DRY too. Should the sending of the email be factored into a service class? perhaps using a filter would work. what are your thoughts?

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  • Avoid loading unnecessary data from db into objects (web pages)

    - by GmGr
    Really newbie question coming up. Is there a standard (or good) way to deal with not needing all of the information that a database table contains loaded into every associated object. I'm thinking in the context of web pages where you're only going to use the objects to build a single page rather than an application with longer lived objects. For example, lets say you have an Article table containing id, title, author, date, summary and fullContents fields. You don't need the fullContents to be loaded into the associated objects if you're just showing a page containing a list of articles with their summaries. On the other hand if you're displaying a specific article you might want every field loaded for that one article and maybe just the titles for the other articles (e.g. for display in a recent articles sidebar). Some techniques I can think of: Don't worry about it, just load everything from the database every time. Have several different, possibly inherited, classes for each table and create the appropriate one for the situation (e.g. SummaryArticle, FullArticle). Use one class but set unused properties to null at creation if that field is not needed and be careful. Give the objects access to the database so they can load some fields on demand. Something else? All of the above seem to have fairly major disadvantages. I'm fairly new to programming, very new to OOP and totally new to databases so I might be completely missing the obvious answer here. :)

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  • Avoid writing SQL queries altogether in SSIS

    - by Jonn
    Working on a Data Warehouse project, the guy that gave us the tutorial advised that we stick to using SQL queries over defining a lot of data flow transformations, citing points like it'll consume a lot of memory on the ETL box so we'd rather leave the processing to the DB box. Is this really advisable? Where's the balance between relying on GUI tools over executing a bunch of SQL scripts on your Integration package? And honestly, I'd like to avoid writing SQL queries as much as I can.

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  • If terminating a hung thread is a good idea, how do I do it safely?

    - by Steve
    My Delphi program relies heavily on Outlook automation. Outlook versions prior to 2007-SP2 tend to get stuck in memory due to badly written addins and badly written Outlook code. If Outlook is stuck, calling CreateOleObject('Outlook.Application') or GetActiveObject ... doesn't return and keeps my application hanging till Outlook.exe is closed in the task manager. I've thought of a solution, but I'm unsure whether it's good practice or not. I'd start Outlook with CreateOleObject in a separate thread, wait 10 seconds in my main thread and if Outlook hangs (CreateOleObject doesn't return), offer the user to kill the Outlook.exe process from my program. But since I don't want to force the user to kill the Outlook.exe process, as an alternative I also need a way to kill the new thread in my program which keeps hanging now. Is this good practice? How can I terminate a hanging thread in Delphi without leaking memory?

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  • What is the Proper approach for Constructing a PhysicalAddress object from Byte Array

    - by Paul Farry
    I'm trying to understand what the correct approach for a constructor that accepts a Byte Array with regard to how it stores it's data (specifically with PhysicalAddress) I have an array of 6 bytes (theAddress) that is constructed once. I have a source array of 18bytes (theAddresses) that is loaded from a TCP Connection. I then copy the 6bytes from theAddress+offset into theAddress and construct the PhysicalAddress from it. Problem is that the PhysicalAddress just stores the Reference to the array that was passed in. Therefore if you subsequently check the addresses they only ever point to the last address that was copied in. When I took a look inside the PhysicalAddress with reflector it's easy to see what's going on. public PhysicalAddress(byte[] address) { this.changed = true; this.address = address; } Now I know this can be solved by creating theAddress array on each pass, but I wanted to find out what really is the best practice for this. Should the constructor of an object that accepts a byte array create it's own private Variable for holding the data and copy it from the original Should it just hold the reference to what was passed in. Should I just created theAddress on each pass in the loop

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  • SOAP - Why do I need to query for the values for an update?

    - by Phill Pafford
    I'm taking over a project and wanted to understand if this is common practice using SOAP. The process that is currently in place I have to query all the values before I do an update cause I need to pass back all the values that are not being updated. Does this sound right? Example Values: fname=phill lname=pafford address=123 main phone:222-555-1212 So if I just wanted to update the phone number I need to query for the record, get all the values and submit these values for an update. Example Update Values: fname=phill lname=pafford address=123 main phone:111-555-1212 I just want to know if this is common practice or should I change the functionality of this?

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  • How to document object-oriented MATLAB code?

    - by jjkparker
    I'm writing a sizable application using object-oriented MATLAB, and this has gotten me thinking about how to document the code. If this was C, I would use Doxygen. For Java, I'd use JavaDoc. Both have mostly agreed-upon standards for how class and method documentation should look and what it should contain. But what about MATLAB code? The most I've seen in TMW's own classes is a short sentence or two at the top of the class, and I can't find any topics devoted to documenting sizable MATLAB applications. So how do you document your MATLAB classes? Any particular style issues or additional tools?

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  • Should a Unit-test replicate functionality or Test output?

    - by Daniel Beardsley
    I've run into this dilemma several times. Should my unit-tests duplicate the functionality of the method they are testing to verify it's integrity? OR Should unit tests strive to test the method with numerous manually created instances of inputs and expected outputs? I'm mainly asking the question for situations where the method you are testing is reasonably simple and it's proper operation can be verified by glancing at the code for a minute. Simplified example (in ruby): def concat_strings(str1, str2) return str1 + " AND " + str2 end Simplified functionality-replicating test for the above method: def test_concat_strings 10.times do str1 = random_string_generator str2 = random_string_generator assert_equal (str1 + " AND " + str2), concat_strings(str1, str2) end end I understand that most times the method you are testing won't be simple enough to justify doing it this way. But my question remains; is this a valid methodology in some circumstances (why or why not)?

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  • Should I define a single "DataContext" and pass references to it around or define muliple "DataConte

    - by Nate Bross
    I have a Silverlight application that consists of a MainWindow and several classes which update and draw images on the MainWindow. I'm now expanding this to keep track of everything in a database. Without going into specifics, lets say I have a structure like this: MainWindow Drawing-Surface Class1 -- Supports Drawing DataContext + DataServiceCollection<T> w/events Class2 -- Manages "transactions" (add/delete objects from drawing) Class3 Each "Class" is passed a reference to the Drawing Surface so they can interact with it independently. I'm starting to use WCF Data Services in Class1 and its working well; however, the other classes are also going to need access to the WCF Data Services. (Should I define my "DataContext" in MainWindow and pass a reference to each child class?) Class1 will need READ access to the "transactions" data, and Class2 will need READ access to some of the drawing data. So my question is, where does it make the most sense to define my DataContext? Does it make sense to: Define a "global" WCF Data Service "Context" object and pass references to that in all of my subsequent classes? Define an instance of the "Context" for each Class1, Class2, etc Have each method that requires access to data define its own instance of the "Context" and use closures handle the async load/complete events? Would a structure like this make more sense? Is there any danger in keeping an active "DataContext" open for an extended period of time? Typical usecase of this application could range from 1 minute to 40+ minutes. MainWindow Drawing-Surface DataContext Class1 -- Supports Drawing DataServiceCollection<DrawingType> w/events Class2 -- Manages "transactions" (add/delete objects from drawing) DataServiceCollection<TransactionType> w/events Class3 DataServiceCollection<T> w/events

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  • What are the worst examples of moral failure in the history of software engineering?

    - by Amanda S
    Many computer science curricula include a class or at least a lecture on disasters caused by software bugs, such as the Therac-25 incidents or Ariane 5 Flight 501. Indeed, Wikipedia has a list of software bugs with serious consequences, and a question on StackOverflow addresses some of them too. We study the failures of the past so that we don't repeat them, and I believe that rather than ignoring them or excusing them, it's important to look at these failures squarely and remind ourselves exactly how the mistakes made by people in our profession cost real money and real lives. By studying failures caused by uncaught bugs and bad process, we learn certain lessons about rigorous testing and accountability, and we make sure that our innocent mistakes are caught before they cause major problems. There are kinds of less innocent failure in software engineering, however, and I think it's just as important to study the serious consequences caused by programmers motivated by malice, greed, or just plain amorality. Thus we can learn about the ethical questions that arise in our profession, and how to respond when we are faced with them ourselves. Unfortunately, it's much harder to find lists of these failures--the only one I can come up with is that apocryphal "DOS ain't done 'til Lotus won't run" story. What are the worst examples of moral failure in the history of software engineering?

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  • Design patterns to avoid

    - by Brian Rasmussen
    A lot of people seem to agree, that the Singleton pattern has a number of drawbacks and some even suggest to avoid the pattern all together. There's an excellent discussion here. Please direct any comments about the Singleton pattern to that question. Are there other design patterns, that should be avoided or used with great care?

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  • Specification: Use cases for CRUD

    - by Mario Ortegón
    I am writing a Product requirements specification. In this document I must describe the ways that the user can interact with the system in a very high level. Several of these operations are "Create-Read-Update-Delete" on some objects. The question is, when writing use cases for these operations, what is the right way to do so? Can I write only one Use Case called "Manage Object x" and then have these operations as included Use Cases? Or do I have to create one use case per operation, per object? The problem I see with the last approach is that I would be writing quite a few pages that I feel do not really contribute to the understanding of the problem. What is the best practice?

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  • Repository vs Data Access

    - by vdh_ant
    Hi guys In the context of the n-tier application, is there a difference between what you would consider your data access classes to be and your repositories? I tend to think yes but I just wanted to see what other thought. My thinking is that the job of the repository is just to contain and execute the raw query itself, where as the data access class would create the context, execute the repository (passing in the context), handle mapping the data model to the domain model and return the result back up... What do you guys think? Also do you see any of this changing in a Linq to XML scenario (assuming that you change the context for the relevant XDocument)? Cheers Anthony

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  • What is the advantage of the 'src/main/java'' convention?

    - by Chris
    I've noticed that a lot of projects have the following structure: Project-A bin lib src main java RootLevelPackageClass.java I currently use the following convention (as my projects are 100% java): Project-A bin lib src RootLevelPackageClass.java I'm not currently using Maven but am wondering if this is a Maven convention or not or if there is another reason. Can someone explain why the first version is so popular these days and if I should adopt this new convention or not? Chris

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