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  • F# pattern matching

    - by Roger Alsing
    What would be the most effective way to express the following code? match cond.EvalBool() with | true -> match body.Eval() with | :? ControlFlowModifier as e -> match e with | Break(scope) -> e :> obj //Break is a DU element of ControlFlowModifier | _ -> next() //other members of CFM should call next() | _ -> next() | false -> null cond.EvalBool returns a boolean result where false should return null and true should either run the entire block again (its wrapped in a func called next) or if the special value of break is found, then the loop should exit and return the break value. Is there any way to compress that block of code to something smaller?

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  • Observer pattern and violation of Single Principality Rule

    - by Devil Jin
    I have an applet which repaints itself once the text has changed Design 1: //MyApplet.java public class MyApplet extends Applet implements Listener{ private DynamicText text = null; public void init(){ text = new DynamicText("Welcome"); } public void paint(Graphics g){ g.drawString(text.getText(), 50, 30); } //implement Listener update() method public void update(){ repaint(); } } //DynamicText.java public class DynamicText implements Publisher{ // implements Publisher interface methods //notify listeners whenever text changes } Isn't this a violation of Single Responsibility Principle where my Applet not only acts as Applet but also has to do Listener job. Same way DynamicText class not only generates the dynamic text but updates the registered listeners. Design 2: //MyApplet.java public class MyApplet extends Applet{ private AppletListener appLstnr = null; public void init(){ appLstnr = new AppletListener(this); // applet stuff } } // AppletListener.java public class AppletListener implements Listener{ private Applet applet = null; public AppletListener(Applet applet){ this.applet = applet; } public void update(){ this.applet.repaint(); } } // DynamicText public class DynamicText{ private TextPublisher textPblshr = null; public DynamicText(TextPublisher txtPblshr){ this.textPblshr = txtPblshr; } // call textPblshr.notifyListeners whenever text changes } public class TextPublisher implments Publisher{ // implements publisher interface methods } Q1. Is design 1 a SPR violation? Q2. Is composition a better choice here to remove SPR violation as in design 2.

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  • Comparing two date ranges within the same table

    - by Danny Herran
    I have a table with sales per store as follows: SQL> select * from sales; ID ID_STORE DATE TOTAL ---------- -------- ---------- -------------------------------------------------- 1 1 2010-01-01 500.00 2 1 2010-01-02 185.00 3 1 2010-01-03 135.00 4 1 2009-01-01 165.00 5 1 2009-01-02 175.00 6 5 2010-01-01 130.00 7 5 2010-01-02 135.00 8 5 2010-01-03 130.00 9 6 2010-01-01 100.00 10 6 2010-01-02 12.00 11 6 2010-01-03 85.00 12 6 2009-01-01 135.00 13 6 2009-01-02 400.00 14 6 2009-01-07 21.00 15 6 2009-01-08 45.00 16 8 2009-01-09 123.00 17 8 2009-01-10 581.00 17 rows selected. What I need to do is to compare two date ranges within that table. Lets say I need to know the differences in sales between 01 Jan 2009 to 10 Jan 2009 AGAINST 01 Jan 2010 to 10 Jan 2010. I'd like to build a query that returns something like this: ID_STORE_A DATE_A TOTAL_A ID_STORE_B DATE_B TOTAL_B ---------- ---------- --------- ---------- ---------- ------------------- 1 2010-01-01 500.00 1 2009-01-01 165.00 1 2010-01-02 185.00 1 2009-01-02 175.00 1 2010-01-03 135.00 1 NULL NULL 5 2010-01-01 130.00 5 NULL NULL 5 2010-01-02 135.00 5 NULL NULL 5 2010-01-03 130.00 5 NULL NULL 6 2010-01-01 100.00 6 2009-01-01 135.00 6 2010-01-02 12.00 6 2009-01-02 400.00 6 2010-01-03 85.00 6 NULL NULL 6 NULL NULL 6 2009-01-07 21.00 6 NULL NULL 6 2009-01-08 45.00 6 NULL NULL 8 2009-01-09 123.00 6 NULL NULL 8 2009-01-10 581.00 So, even if there are no sales in one range or another, it should just fill the empty space with NULL. So far, I've come up with this quick query, but I the "dates" from sales to sales2 sometimes are different in each row: SELECT sales.*, sales2.* FROM sales LEFT JOIN sales AS sales2 ON (sales.id_store=sales2.id_store) WHERE sales.date >= '2010-01-01' AND sales.date <= '2010-01-10' AND sales2.date >= '2009-01-01' AND sales2.date <= '2009-01-10' ORDER BY sales.id_store ASC, sales.date ASC, sales2.date ASC What am I missing?

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  • Calling a method on an unitialized object (null pointer)

    - by Florin
    What is the normal behavior in Objective-C if you call a method on an object (pointer) that is nil (maybe because someone forgot to initialize it)? Shouldn't it generate some kind of an error (segmentation fault, null pointer exception...)? If this is normal behavior, is there a way of changing this behavior (by configuring the compiler) so that the program raises some kind of error / exception at runtime? To make it more clear what I am talking about, here's an example. Having this class: @interface Person : NSObject { NSString *name; } @property (nonatomic, retain) NSString *name; - (void)sayHi; @end with this implementation: @implementation Person @synthesize name; - (void)dealloc { [name release]; [super dealloc]; } - (void)sayHi { NSLog(@"Hello"); NSLog(@"My name is %@.", name); } @end Somewhere in the program I do this: Person *person = nil; //person = [[Person alloc] init]; // let's say I comment this line person.name = @"Mike"; // shouldn't I get an error here? [person sayHi]; // and here [person release]; // and here

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  • spl_object_hash for PHP < 5.2 (unique ID for object instances)

    - by Rowan
    I'm trying to get unique IDs for object instances in PHP 5+. The function, spl_object_hash() is available from PHP 5.2 but I'm wondering if there's a workaround for older versions. There are a couple of functions in the comments on php.net but they're not working for me. The first (simplified): function spl_object_hash($object){ if (is_object($object)){ return md5((string)$object); } return null; } does not work with native objects (such as DOMDocument), and the second: function spl_object_hash($object){ if (is_object($object)){ ob_start(); var_dump($object); $dump = ob_get_contents(); ob_end_clean(); if (preg_match('/^object\(([a-z0-9_]+)\)\#(\d)+/i', $dump, $match)) { return md5($match[1] . $match[2]); } } return null; } looks like it could be a major performance buster! Does anybody have anything up their sleeve?

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  • F# pattern matching when mixing DU's and other values

    - by Roger Alsing
    What would be the most effective way to express the following code? match cond.EvalBool() with | true -> match body.Eval() with | :? ControlFlowModifier as e -> match e with | Break(scope) -> e :> obj //Break is a DU element of ControlFlowModifier | _ -> next() //other members of CFM should call next() | _ -> next() //all other values should call next() | false -> null cond.EvalBool returns a boolean result where false should return null and true should either run the entire block again (its wrapped in a func called next) or if the special value of break is found, then the loop should exit and return the break value. Is there any way to compress that block of code to something smaller?

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  • Passing NULL value

    - by FFXIII
    Hi. I use an instance of NSXMLParser. I store found chars in NSMutableStrings that are stored in an NSMutableDictionary and these Dicts are then added to an NSMutableArray. When I test this everything seems normal: I count 1 array, x dictionnaries and x strings. In a detailview controller file I want to show my parsed results. I call the class where everthing is stored but I get (null) returned. This is what I do (wrong): XMLParser.h @interface XMLParser : NSObject { NSMutableArray *array; NSMUtableDictionary *dictionary; NSSMutabletring *element; } @property (nonatomic, retain) NSMutableArray *array; @property (nonatomic, retain) NSMutableDictionary *dictionary; @property (nonatomic, retain) NSMutableString *element; XMLParser.m @synthesize array, dictionary, element; //parsing goes on here & works fine //so 'element' is filled with content and stored in a dict in an array //and released at the end of the file In my controller file I do this: controller.h @class XMLParser; @interface controller : UIViewController { XMLParser *aXMLParser; } @property (nonatomic, retain) XMLParser *aXMLParser; controller.m #import "XMLParser.h" @synthesize aXMLParser; - (void)viewDidLoad { NSLog(@"test array: %@", aXMLParser.array); NSLog(@"test dict: %@", aXMLParser.dictionary); NSLog(@"test element: %@", aXMLParser.element); } When I test the value of my array, a dict or an element in the XMLParser.h file I get my result. What am I doing wrong so I can't call my results in my controller file? Any help is welcome, because I'm pretty stuck right now :/

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  • Observer pattern and violation of Single Responsibility Principle

    - by Devil Jin
    I have an applet which repaints itself once the text has changed Design 1: //MyApplet.java public class MyApplet extends Applet implements Listener{ private DynamicText text = null; public void init(){ text = new DynamicText("Welcome"); } public void paint(Graphics g){ g.drawString(text.getText(), 50, 30); } //implement Listener update() method public void update(){ repaint(); } } //DynamicText.java public class DynamicText implements Publisher{ // implements Publisher interface methods //notify listeners whenever text changes } Isn't this a violation of Single Responsibility Principle where my Applet not only acts as Applet but also has to do Listener job. Same way DynamicText class not only generates the dynamic text but updates the registered listeners. Design 2: //MyApplet.java public class MyApplet extends Applet{ private AppletListener appLstnr = null; public void init(){ appLstnr = new AppletListener(this); // applet stuff } } // AppletListener.java public class AppletListener implements Listener{ private Applet applet = null; public AppletListener(Applet applet){ this.applet = applet; } public void update(){ this.applet.repaint(); } } // DynamicText public class DynamicText{ private TextPublisher textPblshr = null; public DynamicText(TextPublisher txtPblshr){ this.textPblshr = txtPblshr; } // call textPblshr.notifyListeners whenever text changes } public class TextPublisher implments Publisher{ // implements publisher interface methods } Q1. Is design 1 a SPR violation? Q2. Is composition a better choice here to remove SPR violation as in design 2.

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  • PHP: How do I access child properties from a method in a base object?

    - by Nick
    I'd like for all of my objects to be able to return a JSON string of themselves. So I created a base class for all of my objects to extend, with an AsJSON() method: class BaseObject { public function AsJSON() { $JSON=array(); foreach ($this as $key = $value) { if(is_null($value)) continue; $JSON[$key] = $value; } return json_encode($JSON); } } And then extend my child classes from that: class Package extends BaseObject { ... } So in my code, I expect to do this: $Box = new Package; $Box-SetID('123'); $Box-SetName('12x8x6'); $Box-SetBoxX('12'); $Box-SetBoxY('8'); $Box-SetBoxZ('6'); echo $Box-AsJSON(); But the JSON string it returns only contains the BaseClass's properties, not the child properties. How do I modify my AsJSON() function so that $this refers to the child's properties, not the parent's?

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  • ASP.NET MVC ViewModel Pattern

    - by Omu
    EDIT: I made something much better to fill and read data from a view using ViewModels, called it ValueInjecter. http://valueinjecter.codeplex.com/documentation using the ViewModel to store the mapping logic was not such a good idea because there was repetition and SRP violation, but now with the ValueInjecter I have clean ViewModels and dry mapping code I made a ViewModel pattern for editing stuff in asp.net mvc this pattern is usefull when you have to make a form for editing an entity and you have to put on the form some dropdowns for the user to choose some values public class OrganisationViewModel { //paramterless constructor required, cuz we are gonna get an OrganisationViewModel object from the form in the post save method public OrganisationViewModel() : this(new Organisation()) {} public OrganisationViewModel(Organisation o) { Organisation = o; Country = new SelectList(LookupFacade.Country.GetAll(), "ID", "Description", CountryKey); } //that's the Type for whom i create the viewmodel public Organisation Organisation { get; set; } #region DropDowns //for each dropdown i have a int? Key that stores the selected value public IEnumerable<SelectListItem> Country { get; set; } public int? CountryKey { get { if (Organisation.Country != null) { return Organisation.Country.ID; } return null; } set { if (value.HasValue) { Organisation.Country = LookupFacade.Country.Get(value.Value); } } } #endregion } and that's how i use it public ViewResult Edit(int id) { var model = new OrganisationViewModel(organisationRepository.Get(id)); return View(model); } [AcceptVerbs(HttpVerbs.Post)] public ActionResult Edit(OrganisationViewModel model) { organisationRepository.SaveOrUpdate(model.Organisation); return RedirectToAction("Index"); } and the markup <p> <label for="Name"> Name:</label> <%= Html.Hidden("Organisation.ID", Model.Organisation.ID)%> <%= Html.TextBox("Organisation.Name", Model.Organisation.Name)%> <%= Html.ValidationMessage("Organisation.Name", "*")%> </p> <p> ... <label for="CountryKey"> Country:</label> <%= Html.DropDownList("CountryKey", Model.Country, "please select") %> <%= Html.ValidationMessage("CountryKey", "*") %> </p> so tell me what you think about it

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  • Refactor Regex Pattern - Java

    - by UK
    Hello All, I have the following aaaa_bb_cc string to match and written a regex pattern like \\w{4}+\\_\\w{2}\\_\\w{2} and it works. Is there any simple regex which can do this same ?

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  • Pattern Matching with XSLT

    - by genesis11
    I'm trying to match a pattern into a string in XSLT/XPath using the matches function, as follows: <xsl:when test="matches('awesome','awe')"> ... </xsl:when> However, in both Firefox 3.5.9 and IE8, it doesn't show up. IE8 tells me that "'matches' is not a valid XSLT or XPath function." Is this due to XSLT 2.0 not being supported, and is there a way around this?

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  • java filenames filter pattern

    - by Sergey
    Hello, I need to implement File[] files = getFiles( String folderName, String ptrn ); Where ptrn is a command prompt style pattern like "*2010*.txt" I'm familar with FilenameFilter class, but can't implement public boolean accept(File dir, String filename) because String.matches() doesn't accept such patterns. Thanks!

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  • Java - is this an idiom or pattern, behavior classes with no state

    - by Berlin Brown
    I am trying to incorporate more functional programming idioms into my java development. One pattern that I like the most and avoids side effects is building classes that have behavior but they don't necessarily have any state. The behavior is locked into the methods but they only act on the parameters passed in. The code below is code I am trying to avoid: public class BadObject { private Map<String, String> data = new HashMap<String, String>(); public BadObject() { data.put("data", "data"); } /** * Act on the data class. But this is bad because we can't * rely on the integrity of the object's state. */ public void execute() { data.get("data").toString(); } } The code below is nothing special but I am acting on the parameters and state is contained within that class. We still may run into issues with this class but that is an issue with the method and the state of the data, we can address issues in the routine as opposed to not trusting the entire object. Is this some form of idiom? Is this similar to any pattern that you use? public class SemiStatefulOOP { /** * Private class implies that I can access the members of the <code>Data</code> class * within the <code>SemiStatefulOOP</code> class and I can also access * the getData method from some other class. * * @see Test1 * */ class Data { protected int counter = 0; public int getData() { return counter; } public String toString() { return Integer.toString(counter); } } /** * Act on the data class. */ public void execute(final Data data) { data.counter++; } /** * Act on the data class. */ public void updateStateWithCallToService(final Data data) { data.counter++; } /** * Similar to CLOS (Common Lisp Object System) make instance. */ public Data makeInstance() { return new Data(); } } // End of Class // Issues with the code above: I wanted to declare the Data class private, but then I can't really reference it outside of the class: I can't override the SemiStateful class and access the private members. Usage: final SemiStatefulOOP someObject = new SemiStatefulOOP(); final SemiStatefulOOP.Data data = someObject.makeInstance(); someObject.execute(data); someObject.updateStateWithCallToService(data);

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  • Is scala's cake pattern possible with parametrized components?

    - by Nicolas
    Parametrized components work well with the cake pattern as long as you are only interested in a unique component for each typed component's, example: trait AComponent[T] { val a:A[T] class A[T](implicit mf:Manifest[T]) { println(mf) } } class App extends AComponent[Int] { val a = new A[Int]() } new App Now my application requires me to inject an A[Int] and an A[String], obviously scala's type system doesn't allow me to extends AComponent twice. What is the common practice in this situation ?

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  • Command Design Pattern

    - by pchajer
    After reading command design pattern, I have a couple of question - Why we are creating concrete command and receiver object on client. Can't this initialization on invoker class? I think client should create invoker and pass it's request to invoker. Invoker should take care of all the stuff. By doing this, We have less dependency on client. The design of class diagram is totally different from actual design.

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  • Is loose coupling w/o use cases an anti-pattern?

    - by dsimcha
    Loose coupling is, to some developers, the holy grail of well-engineered software. It's certainly a good thing when it makes code more flexible in the face of changes that are likely to occur in the foreseeable future, or avoids code duplication. On the other hand, efforts to loosely couple components increase the amount of indirection in a program, thus increasing its complexity, often making it more difficult to understand and often making it less efficient. Do you consider a focus on loose coupling without any use cases for the loose coupling (such as avoiding code duplication or planning for changes that are likely to occur in the foreseeable future) to be an anti-pattern? Can loose coupling fall under the umbrella of YAGNI?

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  • Is there a pattern to restrict which classes can update another class?

    - by Mike
    Say I have a class ImportantInfo with a public writable property Data. Many classes will read this property but only a few will ever set it. Basically, if you want to update Data you should really know what you're doing. Is there a pattern I could use to make this explicit other than by documenting it? For example, some way to enforce that only classes that implement IUpdateImportantData can do it (this is just an example)? I'm not talking about security here, but more of a "hey, are you sure you want to do that?" kind of thing.

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  • Associating an object with another object for GC clearup

    - by thecoop
    Is there any way of associating an object instance (object A) with a second object (object B) in a generalised way, so that when B gets collected A becomes eligable for collection? The same behaviour that would happen if B had an instance variable pointing to A, but without explicitly changing the class definition of B, and being able to do this in a dynamic way? The same sort of effect could be done by using the Component.Disposed event in a funky way, but I don't want to make B disposable EDIT I'm basically creating a cache of objects that are associated with a single 'root' object, and I don't want the cache to be static, as there can be lots of root objects using different caches, so lots of memory will be used up when a root object is no longer used but the cached objects are still around. So, I want a collection of cached objects to be associated with each 'root' object, without changing the root object definition. Sort of like metadata of an extra object reference attached to each root object instance. That way, each collection will get collected when the root object is collected, and not hang around like they would if a static cache was used.

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  • ASP.Net repeater item.DataItem is null

    - by mattgcon
    Within a webpage, upon loading, I fill a dataset with two table with a relation between those tables and then load the data into a repeater with a nested repeater. This can also occur after the user clicks on a button. The data gets loaded from a SQL database and the repeater datasource is set to the dataset after a postback. However, when ItemDataBound occurs the Item.Dataitem is always null. Why would this occur? below is my HTML repeater code <asp:Repeater ID="rptCustomSpaList" runat="server" onitemdatabound="rptCustomSpaList_ItemDataBound"> <HeaderTemplate> </HeaderTemplate> <ItemTemplate> <table> <tr> <td> <asp:Label ID="Label3" runat="server" Text="Spa Series:"></asp:Label> </td> <td> <asp:Label ID="Label4" runat="server" Text='<%#DataBinder.Eval(Container.DataItem, "SPASERIESVALUE") %>'></asp:Label> </td> </tr> <tr> <td> <asp:Label ID="Label5" runat="server" Text="Spa Model:"></asp:Label> </td> <td> <asp:Label ID="Label6" runat="server" Text='<%#DataBinder.Eval(Container.DataItem, "SPAMODELVALUE") %>'></asp:Label> </td> </tr> <tr> <td> <asp:Label ID="Label9" runat="server" Text="Acrylic Color:"></asp:Label> </td> <td> <asp:Label ID="Label10" runat="server" Text='<%#DataBinder.Eval(Container.DataItem, "ACRYLICCOLORVALUE") %>'></asp:Label> </td> </tr> <tr> <td> <asp:Label ID="Label11" runat="server" Text="Cabinet Color:"></asp:Label> </td> <td> <asp:Label ID="Label12" runat="server" Text='<%#DataBinder.Eval(Container.DataItem, "CABPANCOLORVALUE") %>'></asp:Label> </td> </tr> <tr> <td> <asp:Label ID="Label17" runat="server" Text="Cabinet Type:"></asp:Label> </td> <td> <asp:Label ID="Label18" runat="server" Text='<%#DataBinder.Eval(Container.DataItem, "CABINETVALUE") %>'></asp:Label> </td> </tr> <tr> <td> <asp:Label ID="Label13" runat="server" Text="Cover Color:"></asp:Label> </td> <td> <asp:Label ID="Label14" runat="server" Text='<%#DataBinder.Eval(Container.DataItem, "COVERCOLORVALUE") %>'></asp:Label> </td> </tr> </table> <asp:Label ID="Label15" runat="server" Text="Options:"></asp:Label> <asp:Repeater ID="rptCustomSpaItem" runat="server"> <HeaderTemplate> <table> </HeaderTemplate> <ItemTemplate> <tr> <td> <asp:Label ID="Label1" runat="server" Text='<%#DataBinder.Eval(Container.DataItem, "PROPERTY") %>'></asp:Label> </td> <td> <asp:Label ID="Label2" runat="server" Text='<%#DataBinder.Eval(Container.DataItem, "VALUE") %>'></asp:Label> </td> </tr> </ItemTemplate> <FooterTemplate> </table> </FooterTemplate> </asp:Repeater> <table> <tr> <td style="padding-top:15px;padding-bottom:30px;"> <asp:Label ID="Label7" runat="server" Text="Configured Price:"></asp:Label> </td> <td style="padding-top:15px;padding-bottom:30px;"> <asp:Label ID="Label8" runat="server" Text='<%#DataBinder.Eval(Container.DataItem, "SPAVALUEVALUE") %>'></asp:Label> </td> </tr> </table> <asp:Label ID="Label16" runat="server" Text="------"></asp:Label> </ItemTemplate> <FooterTemplate></FooterTemplate> </asp:Repeater>

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