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  • How to write curiously recurring templates with more than 2 layers of inheritance?

    - by Kyle
    All the material I've read on Curiously Recurring Template Pattern seems to one layer of inheritance, ie Base and Derived : Base<Derived>. What if I want to take it one step further? #include <iostream> using std::cout; template<typename LowestDerivedClass> class A { public: LowestDerivedClass& get() { return *static_cast<LowestDerivedClass*>(this); } void print() { cout << "A\n"; } }; template<typename LowestDerivedClass> class B : public A<LowestDerivedClass> { public: void print() { cout << "B\n"; } }; class C : public B<C> { public: void print() { cout << "C\n"; } }; int main() { C c; c.get().print(); // B b; // Intentionally bad syntax, // b.get().print(); // to demonstrate what I'm trying to accomplish return 0; } How can I rewrite this code to compile without errors (and output "C\nB\n")?

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  • shell script segment to avoid overwriting files

    - by johndashen
    I have a perl script (or any executable) E which will take a file foo.xml and write a file foo.txt. I use a Beowulf cluster to run E for a large number of XML files, but I'd like to write a simple job server script in shell (bash) which doesn't overwrite existing txt files. I'm currently doing something like #!/bin/sh PATTERN="[A-Z]*0[1-2][a-j]"; # this matches foo in all cases todo=`ls *.xml | grep $PATTERN`; isdone=`ls *.foo | grep $PATTERN`; whatsleft=todo - isdone; # what's the unix magic? #and then call the job server; jobserve E "$whatsleft"; and then I don't know how to get the difference between $todo and $isdone. I'd prefer using sort/uniq to something like a for loop with grep inside, but I'm not sure how to do it (pipes? temporary files?) As a bonus question, is there a way to do lookahead search in bash grep?

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  • Expandable columns in a datagrid

    - by Jobe
    Im working on a WPF-applications to present and correct large amounts of data. Im about to implement a datagrid containing data from 3 different sources that are populated from external services. To start with I will only populate the grid with data from one source, the master source. However, sometimes an automated validator will trigger a validation warning or error on one cell and the requirement states that the user should be able to view data from the additional 2 sources in columns next to the selected one. Something like this: Standard view: | col1 src1 | col2 src1 | col3 src1 | | | | | | |faulty | | | | | | User want to show data from source 2 and 3 next to the column "col2 src1" like this: | col1 src1 | col2 src1 | col2 src2 | col2 src3 | col3 src1 | | | | | | | | |corrected | | | | | | | | | | and then be able to correct the faulty formatted cell with data from the other 2 soruces, and then collapse the columns again. I am trying to use the mvvm pattern on this one so I have populated the DataGrid with a ListCollectionView so far. The list contains items with properties like this: MyRowItem {string col1, string col2, string col3} I will then have 2 additional collections with items of type like above but from 2 other sources. I have no idea how to implement this functionality and could use some help on the logics. What approach should I head for?

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  • Pick up relevant information from a string using regular expression C#3.0

    - by Newbie
    Hi, I have a situation. I have been given some file name which can be like <filename>YYYYMMDD<fileextension> some valid file names that will satisfy the above pattern are as under xxx20100326.xls, xxx2v20100326.csv, x_20100326.xls, xy2z_abc_20100326_xyz.csv, abc.xyz.20100326.doc, ab2.v.20100326.doc, abc.v.20100326_xyz.xls In what ever be the above defined case, I need to pick up the dates only. So for all the cases, the output will be 20100326. I am trying to achieve the same but no luck. Here is what I have done so far string testdata = "x2v20100326.csv"; string strYYYY = @"\d{4}"; string strMM = @"(1[0-2]|0[1-9])"; string strDD = @"(3[0-1]|[1-2][0-9]|0[1-9])"; string regExPattern = @"\A" + strYYYY + strMM + strDD + @"\Z"; Regex regex = new Regex(regExPattern); Match match = regex.Match(testdata); if (match.Success) { string result = match.Groups[0].Value; } I am using c#3.0 and dotnet framework 3.5 Please help. It is very urgent Thanks in advance.

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  • Mono Develop 2.4.1 + linq error.

    - by Nev_Rahd
    I just started to learn Mono Develop Installed Mono Develop 2.4.1 and trial version of Mono Touch. my Code: using System; using System.Xml.Linq; using System.Collections.Generic; namespace RSSReader { public static class RSSRepository { public static IList<FeedItem> GetFeeds(string url) { XDocument rssFeed = XDocument.Load(url); Console.Write(rssFeed.ToString()); var feeds = new List<FeedItem>(); try { var query = from item in rssFeed.Descendants("item") select new FeedItem { Title = item.Element("title").Value, Published = DateTime.Parse(item.Element("pubDate").Value), Url = item.Element("link").Value }; feeds = query.ToList(); } catch (Exception ex){ Console.WriteLine(ex.Message); } return feeds; } } } This is throwing an error: An implementation of 'select' query expression pattern could not be found. Are you missing 'System.linq' using directive or 'System.Core.dll' assembly reference? I got both references to System.Xml.Linq and System.Core What am i missing ?

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  • Is it OK to set state within Event Raising methods?

    - by Greg
    I ran across this pattern in the code of a library I'm using. It sets state within the event raising method, but only if the event is not null. protected virtual void OnMyEvent(EventArgs e) { if(MyEvent != null) { State = "Executing"; // Only sets state if MyEvent != null. MyEvent(this,e); } } Which means that the state is not set when overriding the method: protected override void OnMyEvent(EventArgs e) { base.OnMyEvent(e); Debug.Assert( State == "Executing" ); // This fails } but is only set when handling the event: foo.MyEvent += (o, args) => Debug.Assert(State == "Executing"); // This passes Setting state within the if(MyEvent != null) seems like bad form, but I've checked the Event Design Guidelines and it doesn't mention this. Do you think this code is incorrect? If so, why? (Reference to design guidelines would be helpful). Edit for Context: It's a Control, I'm trying to create subclass of it, and the state that it's setting is calling EnsureChildControls() conditionally based upon there being an event handler. I can call EnsureChildControls() myself, but I consider that something of a hack.

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  • Zend_Router requirements mismatch

    - by elbicho
    Hello you all: I have two routes that match a url with the same apparent pattern, the difference lies in the $actionRoute, this should only be matched if the variable :action on it equals 'myaction'. If I go to /en/mypage/whatever/myaction it goes as expected through $actionRoute. If I go to /en/mypage/whatever/blahblah it gets rejected by $actionRoute and matched by $genRoute. If I go to /en/mypage/whatever it should be matched by $genRoute but it gets matched by $actionRoute instead throwing and exception because the action noactionAction() does not exist. Don't know what I'm doing wrong, I'd appreciate your help. $genRoute = new Zend_Controller_Router_Route( ':lang/mypage/:var1/:var2', array( 'lang' => '', 'module' => 'mymodule', 'controller' => 'index', 'action' => 'index', 'var1' => 'noone', 'var2' => 'no' ), array( 'var1' => '[a-z\-]+?', 'lang' => '(es|en|fr|de){1}' ) ); $actionRoute = new Zend_Controller_Router_Route( ':lang/mypage/:var1/:action', array( 'lang' => '', 'module' => 'mymodule', 'controller' => 'index', 'action' => 'noaction', 'var1' => 'noone', ), array( 'action' => '(myaction)+?', 'var' => '[a-z\-]+?', 'lang' => '(es|en|fr|de){1}', ) ); $router->addRoute('genroute',$genRoute); $router->addRoute('actionroute',$actionRoute);

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  • Caching vector addition over changing collections

    - by DRMacIver
    I have the following setup: I have a largish number of uuids (currently about 10k but expected to grow unboundedly - they're user IDs) and a function f : id - sparse vector with 32-bit integer values (no need to worry about precision). The function is reasonably expensive (not outrageously so, but probably on the order of a few 100ms for a given id). The dimension of the sparse vectors should be assumed to be infinite, as new dimensions can appear over time, but in practice is unlikely to ever exceed about 20k (and individual results of f are unlikely to have more than a few hundred non-zero values). I want to support the following operations efficiently: add a new ID to the collection invalidate an existing ID retrieve sum f(id) in O(changes since last retrieval) i.e. I want to cache the sum of the vectors in a way that's reasonable to do incrementally. One option would be to support a remove ID operation and treat invalidation as a remove followed by an add. The problem with this is that it requires us to keep track of all the old values of f, which is expensive in space. I potentially need to use many instances of this sort of cached structure, so I would like to avoid that. The likely usage pattern is that new IDs are added at a fairly continuous rate and are frequently invalidated at first. Ids which have been invalidated recently are much more likely to be invalidated again than ones which have remained valid for a long time, but in principle an old Id can still be invalidated. Ideally I don't want to do this in memory (or at least I want a way that lets me save the result to disk efficiently), so an idea which lets me piggyback off an existing DB implementation of some sort would be especially appreciated.

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  • Creating mock Objects in PHP unit

    - by Mike
    Hi, I've searched but can't quite find what I'm looking for and the manual isn't much help in this respect. I'm fairly new to unit testing, so not sure if I'm on the right track at all. Anyway, onto the question. I have a class: <?php class testClass { public function doSomething($array_of_stuff) { return AnotherClass::returnRandomElement($array_of_stuff); } } ?> Now, clearly I want the AnotherClass::returnRandomElement($array_of_stuff); to return the same thing every time. My question is, in my unit test, how do I mockup this object? I've tried adding the AnotherClass to the top of the test file, but when I want to test AnotherClass I get the "Cannot redeclare class" error. I think I understand factory classes, but I'm not sure how I would apply that in this instance. Would I need to write an entirely seperate AnotherClass class which contained test data and then use the Factory class to load that instead of the real AnotherClass? Or is using the Factory pattern just a red herring. I tried this: $RedirectUtils_stub = $this->getMockForAbstractClass('RedirectUtils'); $o1 = new stdClass(); $o1->id = 2; $o1->test_id = 2; $o1->weight = 60; $o1->data = "http://www.google.com/?ffdfd=fdfdfdfd?route=1"; $RedirectUtils_stub->expects($this->any()) ->method('chooseRandomRoot') ->will($this->returnValue($o1)); $RedirectUtils_stub->expects($this->any()) ->method('decodeQueryString') ->will($this->returnValue(array())); in the setUp() function, but these stubs are ignored and I can't work out whether it's something I'm doing wrong, or the way I'm accessing the AnotherClass methods. Help! This is driving me nuts.

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  • Zend Framework: How to display multiple actions, each requiring different authorizations levels, on

    - by Iain
    Imagine I have 4 database tables, and an interface that presents forms for the management of the data in each of these tables on a single webpage (using the accordion design pattern to show only one form at a time). Each form is displayed with a list of rows in the table, allowing the user to insert a new row or select a row to edit or delete. AJAX is then used to send the request to the server. A different set of forms must be displayed to different users, based on the application ACL. My question is: In terms of controllers, actions, views, and layouts, what is the best architecture for this interface? For example, so far I have a controller with add, edit and delete actions for each table. There is an indexAction for each, but it's an empty function. I've also extended Zend_Form for each table. To display the forms, I then in the IndexController pass the Forms to it's view, and echo each form. Javascript then takes care of populating the form and sending requests to the appropraite add/edit/delete action of the appropriate controller. This however doesn't allow for ACL to control the display or not of Forms to different users. Would it be better to have the indexAction instantiate the form, and then use something like $this-render(); to render each view within the view of the indexAction of the IndexController? Would ACL then prevent certain views from being rendered? Cheers.

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  • Managing a log stream in C++ in a cout-like notation

    - by Andry
    Hello! I have a class in c++ in order to write log files for an application of mine. I have already built the class and it works, it is something like this: class Logger { std::string _filename; public: void print(std::string tobeprinted); } Well, it is intuitive that, in order to print a line in the log file, for an object of Logger, it is simply necessary to do the following: Logger mylogger("myfile.log"); mylogger.print(std::string("This is a log line")); Well. Using a method approach is not the same as using a much better pattern like << is. I would like to do the following: Logger mylogger("myfile.log"); mylogger << "This is a log line"; That's all. I suppose I must overload the << operator... But overloading using this signature (the classic one): ostream& operator<<(ostream& output, const MyObj& o); But I do not have a ostream... So, should I do as follows? Logger& operator<<(Logger& output, const std::string& o); Is this the right way? Thanks

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  • Design patterns for Caching Images in a MVC?

    - by Onema
    Hi, I'm designing an image cache system that will be used in an MVC CMS. The main purpose of the image cacher is to modify images: scale, crop, etc and cache them in the client site. I have created an image cache Model and Mapper that interact with the Database, to keep track of the images and know what kind of actions have been applied to them (scale, crop, etc). In addition to the Model and Mapper I have created a ImageCacher Class that is used by the API to manage the Model and image creation based on arguments passed by the client site, this class creates the images and generates the links to the images for the View. A coworker argued that I need to include the functionality of this last Class inside the Model, as the bulk of the logic should go in the model. I respectfully disagree with him since I feel the model's responsibility is to deal with the information about the images cached at the database level, and the responsibility of the ImageCacher Class is to create the url/image that we will be caching (keeping the single responsibility principle). In addition to this I believe that a model should not have Presentation-related features, like creating or showing images. Does anyone have any insight on this? is there a particular design pattern that would make this division of tasks clear and and the image cacher reusable? Should I add all the logic in the Model? Thank you.

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  • Manual Linq to SQL entity framework mapping

    - by kprobst
    I've been playing with the O/R designer in VS and I was wondering if someone could shed come light on this. I'm used to OR mappers that are largely manual (homegrown and e.g., NHibernate). I don't mind encoding the entity classes myself, since they don't change all that often to begin with, and I have this irrational fear of designers and auto generated code as it is. I have noticed that the generated entity classes contain a lot of boilerplate extensibility methods, e.g. On[Property]Changed() and so on where [Property] is a mapped member of the class. These are placed in the setters of the property accessors. I assume it's OK if I don't include these when I do my hand coding, correct? They would be nice if I needed some sort of interception pattern but that's certainly not the case. I guess I just need to know if any of those methods are required by the entity framework to keep track of changes to the mapping types in order for things to work when updating the database. Thanks!

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  • Wouldn't it be nice to have a type variable referring to the class's instance.

    - by user93197
    I often have a pattern like this: class VectorBase<SubClass, Element> where SubClass : VectorBase<SubClass, Element>, new() where Element : Addable<Element> { Element[] data; public VectorBase(Element[] data) { this.data = data; } public SubClass add(SubClass second) { Element[] newData = new Element[data.Length]; for (int i = 0; i < newData.Length; i++) { newData[i] = data[i].add(second.data[i]); } SubClass result = new SubClass(); result.data = newData; return result; } } class VectorInt : VectorBase<VectorInt, Int32> { } class MyInt : Addable<MyInt> { int data; public MyInt(int data) { this.data = data; } public MyInt add(MyInt t) { return new MyInt(data + t.data); } } interface Addable<T> { T add(T t); } But I would rather just have: class VectorBase2<Element> where Element : Addable<Element> { Element[] data; public VectorBase(Element[] data) { this.data = data; } public SubClass add(SubClass second) { Element[] newData = new Element[data.Length]; for (int i = 0; i < newData.Length; i++) { newData[i] = data[i].add(second.data[i]); } SubClass result = new SubClass(data); return result; } } class VectorInt2 : VectorBase2<Int32> { } Why not make the subclass type available to all classes? Is this technically impossible?

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  • Refactoring. Your way to reduce code complexity of big class with big methods

    - by Andrew Florko
    I have a legacy class that is rahter complex to maintain: class OldClass { method1(arg1, arg2) { ... 200 lines of code ... } method2(arg1) { ... 200 lines of code ... } ... method20(arg1, arg2, arg3) { ... 200 lines of code ... } } methods are huge, unstructured and repetitive (developer loved copy/paste aprroach). I want to split each method into 3-5 small functions, whith one pulic method and several helpers. What will you suggest? Several ideas come to my mind: Add several private helper methods to each method and join them in #region (straight-forward refactoring) Use Command pattern (one command class per OldClass method in a separate file). Create helper static class per method with one public method & several private helper methods. OldClass methods delegate implementation to appropriate static class (very similiar to commands). ? Thank you in advance!

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  • Memory allocation patterns in C++

    - by Mahatma
    I am confused about the memory allocation in C++ in terms of the memory areas such as Const data area, Stack, Heap, Freestore, Heap and Global/Static area. I would like to understand the memory allocation pattern in the following snippet. Can anyone help me to understand this. If there any thing more apart from the variable types mentioned in the example to help understand the concept better please alter the example. class FooBar { int n; //Stored in stack? public: int pubVar; //stored in stack? void foo(int param) //param stored in stack { int *pp = new int; //int is allocated on heap. n = param; static int nStat; //Stored in static area of memory int nLoc; //stored in stack? string str = "mystring"; //stored in stack? .. if(CONDITION) { static int nSIf; //stored in static area of memory int loopvar; //stored in stack .. } } } int main(int) { Foobar bar; //bar stored in stack? or a part of it? Foobar *pBar; //pBar is stored in stack pBar = new Foobar(); //the object is created in heap? What part of the object is stored on heap } EDIT: What confuses me is, if pBar = new Foobar(); stores the object on the heap, how come int nLoc; and int pubVar;, that are components of the object stored on stack? Sounds contradictory to me. Shouldn't the lifetime of pubvar and pBar be the same?

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  • perl DateTime now() problem

    - by Sergey Sinkovskiy
    Having this script use DateTime; use DateTime::Format::Strptime; my $p = DateTime::Format::Strptime->new(pattern => '%F %T', time_zone => 'local'); my $dt1 = DateTime->now(time_zone=>'local')->set_time_zone('UTC'); my $dt2 = $p->parse_datetime('2010-10-23 14:10:02')->set_time_zone('UTC'); print Dumper($dt1->hms); print Dumper($dt2->hms); print Dumper($dt1 > $dt2); The problem is that $dt1 is off by 1 hour. Like $VAR1 = '12:09:55'; $VAR1 = '11:10:02'; $VAR1 = 1; If I remove set_time_zone('UTC') in both cases - dumped values are okay. My feel is that somewhere DST is taken into account unnecessarily, but can't find out. Update: I dumped $dt-time_zone-name and $dt-offset for both and that's what i get. $VAR1 = 'Europe/Kiev'; $VAR1 = 7200; $VAR1 = 'Europe/Kiev'; $VAR1 = 10800; How this could be possible?

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  • Implementing a Version check between an Abstract class and it's implementation

    - by Michael Stum
    I have this abstract class and concrete implementation (they are in different assemblies): public abstract class MyAbstractClass { private static readonly int MyAbstractClassVersion = 1; public abstract int ImplementedVersion { get; } protected MyAbstractClass() { CheckVersion(); } private void CheckVersion() { var message = string.Format( "MyAbstractClass implements Version {0}, concrete is Version {1}", RepositoryVersion, ImplementedVersion); if (!MyAbstractClassVersion.Equals(ImplementedVersion)) throw new InvalidOperationException(message); } } public class ConcreteClass : MyAbstractClass { public ConcreteClass() : base() { // ConcreteClass is guaranteed to have // a constructor that calls the base constructor // I just simplified the example } public override int ImplementedVersion { get { return 2; } } } As you see, I call CheckVersion() from the abstract constructor, to get rid of the "virtual member call in base constructor" message, but I am not sure if that's really the way to do it. Sure, it works, but that doesn't mean it will always work, will it? Also, I wonder if I can get the name of the Concrete Type from the CheckVersion() function? I know that adding new abstract members will force an error anyway (System.TypeLoadException) and I'm not sure if I want this type of strict Versioning, but I'm just curious how it would be done properly given only the abstract class and an implementation (I know I could do it by using interfaces and/or a Factory pattern).

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  • What's the best practice for make username check like Twitter ?

    - by Space Cracker
    I develop registration form and it have username field, and it's required to be like twitter username check ( real time check ) .. i already develop as in every textbox key up I use jquery to pass textbox.Text to page that return if is username exist or not as following code : function Check() { var userName = $('#<%= TextBox1.ClientID %>').val(); if (userName.length < 3) { $('#checkUserNameDIV').html("user name must be between 3 and 20"); return; } $('#checkUserNameDIV').html('<img src="loader.gif" />'); //setTimeout("CheckExistance('" + userName + "')", 5000); CheckExistance(userName); } function CheckExistance(userName) { $.get( "JQueryPage.aspx", { name: userName }, function(result) { var msg = ""; if (result == "1") msg = "Not Exist " + '<img src="unOK.gif" />'; else if (result == "0") msg = "Exist" ; else if (result == "error") msg = "Error , try again"; $('#checkUserNameDIV').html(msg); } ); } but i don't know if is it the best way to do that ? specially i do check every keyup .. is there any design pattern for this problem or nay good practice for doing that ?

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  • Complexity of subset product

    - by threenplusone
    I have a set of numbers produced using the following formula with integers 0 < x < a. f(x) = f(x-1)^2 % a For example starting at 2 with a = 649. {2, 4, 16, 256, 636, 169, 5, 25, 649, 576, 137, ...} I am after a subset of these numbers that when multiplied together equals 1 mod N. I believe this problem by itself to be NP-complete (based on similaries to Subset-Sum problem). However starting with any integer (x) gives the same solution pattern. Eg. a = 649 {2, 4, 16, 256, 636, 169, 5, 25, 649, 576, 137, ...} = 16 * 5 * 576 = 1 % 649 {3, 9, 81, 71, 498, 86, 257, 500, 135, 53, 213, ...} = 81 * 257 * 53 = 1 % 649 {4, 16, 256, 636, 169, 5, 25, 649, 576, 137, 597, ...} = 256 * 25 * 137 = 1 % 649 I am wondering if this additional fact makes this problem solvable faster? Or if anyone has run into this problem previously or has any advice?

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  • HTML5 Canvas and Game Programming

    - by LemonBeagle
    I hope this isn't too open ended. I'm wondering if there is a better (more battery-friendly) way of doing this -- I have a small HTML 5 game, drawn in a canvas (let's say 500x500). I have some objects whose positions I update every 50ms or so. My current implementation re-draws the entire canvas every 50ms. I can't imagine that being very good for battery life on mobile platforms. Is there a better way to do this? This must be a common pattern with games. EDIT: as requested, here are some more updates: Right now, the objects are geometric primitives drawn via arcs and lines. I'm not opposed to making these small png/jpg/gif files instead of that'd help out. These are small graphics -- just 15x15 or so. As the game progresses, more and more of the screen changes at a time. However, at the start, the screen changes relatively slowly (the objects randomly moved a few pixels every 50ms).

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  • How to determine if a target will be executed?

    - by Scott Langham
    Hi, I'm writing an msbuild file and have something like this: <ValidateDependsOn>$(ValidateDependsOn);ValidateA</ValidateDependsOn> <ValidateDependsOn>$(ValidateDependsOn);ValidateB</ValidateDependsOn> <Target Name="BuildA"> <!-- stuff --> </Target> <Target Name="BuildB"> <!-- stuff --> </Target> <Target Name="ValidateA"> <Error /> <!-- check properties and machine environment are suitable to run BuildA --> </Target> <Target Name="ValidateB"> <Error /> <!-- check properties and machine environment are suitable to run BuildB --> </Target> Builds can take a while. Originally we had the Build steps depending on the Validate steps, but sometimes a validate step wouldn't run until the middle of the build and you would have wasted time getting there. So, we moved the validate steps to the start by using the ValidateDependsOn pattern to insert the targets to run up front. The problem now though is that sometimes during a build BuildB may not actually run, and this means I don't need and in fact, don't want ValidateB to run. Is there any way I can selectively update ValidateDependsOn by conditionally knowing which targets will actually be run? I'm looking for something equivalent to: <ValidateDependsOn Condition="TargetWillRun(BuildB)">$(ValidateDependsOn);ValidateB</ValidateDependsOn>

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  • SQL Server 2008 Prior String Extract

    - by Saidur Rahman
    I have strings like the ones below in a SQL column. I want to extract them as a Gigabyte amount in aggregate. Example: Original Column ---------> Expected Output from a TSQL function ------------------------------------------- $15 / 1GB 24m + Intern 120MB ----------> 1.12 GB $19.95 / 500MB + $49.95 / 9GB Blackberry -----> 9.5GB $174.95 Blackberry 24GB + $10 / 1GB Datapack ----> 25GB $79 / 6GB --> 6GB Null --> Null $20 Plan --> 0GB Note: for our purpose, 1000MB = 1 GB (not 1024). The pattern is numbers followed by GB/MB, usually they are combined like 1GB (without any space but may sometimes may contain a space, it is not particularly important if hard to implement for this exception). Sometimes there are up to three or four instances of GB/MB occurring in the same string which are usually separated by a + sign (see row 2 and 3 of my example above). I have seen how we extract the dollar values in one of the answers where numbers were followed by $ or extract all integers in a string but I don't want to extract the dollar values or all the integers in a string. I just want the sum of GB/MB in the string.

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  • Ways to make (relatively) safe assumptions about the type of concrete subclasses?

    - by Kylotan
    I have an interface (defined as a abstract base class) that looks like this: class AbstractInterface { public: bool IsRelatedTo(const AbstractInterface& other) const = 0; } And I have an implementation of this (constructors etc omitted): class ConcreteThing { public: bool IsRelatedTo(const AbstractInterface& other) const { return m_ImplObject.has_relationship_to(other.m_ImplObject); } private: ImplementationObject m_ImplObject; } The AbstractInterface forms an interface in Project A, and the ConcreteThing lives in Project B as an implementation of that interface. This is so that code in Project A can access data from Project B without having a direct dependency on it - Project B just has to implement the correct interface. Obviously the line in the body of the IsRelatedTo function cannot compile - that instance of ConcreteThing has an m_ImplObject member, but it can't assume that all AbstractInterfaces do, including the other argument. In my system, I can actually assume that all implementations of AbstractInterface are instances of ConcreteThing (or subclasses thereof), but I'd prefer not to be casting the object to the concrete type in order to get at the private member, or encoding that assumption in a way that will crash without a diagnostic later if this assumption ceases to hold true. I cannot modify ImplementationObject, but I can modify AbstractInterface and ConcreteThing. I also cannot use the standard RTTI mechanism for checking a type prior to casting, or use dynamic_cast for a similar purpose. I have a feeling that I might be able to overload IsRelatedTo with a ConcreteThing argument, but I'm not sure how to call it via the base IsRelatedTo(AbstractInterface) method. It wouldn't get called automatically as it's not a strict reimplementation of that method. Is there a pattern for doing what I want here, allowing me to implement the IsRelatedTo function via ImplementationObject::has_relationship_to(ImplementationObject), without risky casts? (Also, I couldn't think of a good question title - please change it if you have a better one.)

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  • Need an advice for ASP.NET MVC2 Newsletter Project

    - by ck3g
    I'm new in ASP.NET MVC2. But I want to develop a simply Newsletter site. The main problem which stuck me is how correctly use MVC pattern in News details and comments list. For example: I have a NewsController and action Details inside. And two model classes News and Comments. I want show all comments belongs to this News record and textarea for adding new comments. I wand display all this content in /News/Details/ How can i do it? I tried use PartialViews in Details View: one for Adding Comment and another for Comment list. I have passed comment object thorough ViewData["Comment"]. But i have problems with my models (think I cant use two models in View) Again. How can I display Single Post + Comments + add comment view at single page using ASP.NET MVC2? Another Example is stackoverflow.com. Here is an question + answers + write answer. I need same structure

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