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  • How can I define an empty array in a Perl construtor?

    - by Laimoncijus
    I am just beginner with Perl, so if it sounds stupid - sorry for that :) My problem is - I am trying to write a class, which has an empty array, defined in constructor of a class. So I am doing this like this: package MyClass; use strict; sub new { my ($C) = @_; my $self = { items => () }; bless $self, ref $C || $C; } sub get { return $_[0]->{items}; } 1; Later I am testing my class with simple script: use strict; use Data::Dumper; use MyClass; my $o = MyClass->new(); my @items = $o->get(); print "length = ", scalar(@items), "\n", Dumper(@items); And while running the script I get following: $ perl my_test.pl length = 1 $VAR1 = undef; Why am I doing wrong what causes that I get my items array filled with undef? Maybe someone could show me example how the class would need to be defined so I would not get any default values in my array?

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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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  • Events in Classes (VB.NET)

    - by Otaku
    I find that I write a lot of code within my classes to keep properties in sync with each other. I've read about Events in Classes, but have not been able to wrap my head around how to make them work for what I'm looking for. I could use some advice here. For example, in this one I always want to keep myColor up to date with any change whatsoever in any or all of the Red, Green or Blue properties. Class myColors Private Property Red As Byte Private Property Green As Byte Private Property Blue As Byte Private Property myColor As Color Sub New() myColor = Color.FromArgb(0, 0, 0) End Sub Sub ChangeRed(ByVal r As Byte) Red = r myColor = Color.FromArgb(Red, Green, Blue) End Sub Sub ChangeBlue(ByVal b As Byte) Blue = b myColor = Color.FromArgb(Red, Green, Blue) End Sub End Class If one or more of those changes, I want myColor to be updated. Easy enough as above, but is there a way to work with events that would automatically do this so I don't have to put myColor = Color.FromArgb(Red, Green, Blue) in every sub routine?

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  • domain modeling naming problem

    - by cherouvim
    Hello There are some simple entities in an application (e.g containing only id and title) which rarely change and are being referenced by the more complex entities of the application. These are usually entities such as Country, City, Language etc. How are these called? I've used the following names for those in the past but I'm not sure which is the best way to call them: reference data lookup values dictionaries thanks

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  • Is the a pattern for iterating over lists held by a class (dynamicly typed OO languages)

    - by Roman A. Taycher
    If I have a class that holds one or several lists is it better to allow other classes to fetch those lists(with a getter) or to implement a doXList/eachXList type method for that list that take a function and call that function on each element of the list contained by that object. I wrote a program that did a ton of this and I hated passing around all these lists sometimes with method in class a calling method in class B to return lists contained in class C, B contains a C or multiple C's (note question is about dynamically typed OO languages languages like ruby or smalltalk) ex. (that came up in my program) on a Person class containing scheduling preferences and a scheduler class needing to access them.

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  • What patterns exist for web application development?

    - by DaveDev
    I understand that MVC & MVP are design patterns that are commonly used for web development, as well as ASP.NET WebForms (more of an anti-pattern, really!). What other patterns are used in web application development? I'm not necessarily saying I want to learn/use new patterns just to be different - I do believe there's a lot of value in taking the conventional route - but I think it's good to know what else is out there to be able to properly understand what I'm currently working with. Thanks.

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  • Document -> Flash viewer, not hosted

    - by Dane
    I've got a content management solution where we present scanned images (TIFF), PDFs, word docs for viewing. While we can simply embed a PDF, sometimes depending on user preferences it's a bit fiddly and sometimes not user-intuitive. I'd like a solution like scribd, embedit, etc, but not hosted. I want to run the application on our own servers and manage it that way (for legal reasons, and our clients won't buy the service if it's hosted somewhere else). SWFtools looks a little basic for my needs, plus doesn't do doc, docx or ppt. Any options? Doesn't have to be free, but would be ideal.

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  • C++ inheritance and member function pointers

    - by smh
    In C++, can member function pointers be used to point to derived (or even base) class members? EDIT: Perhaps an example will help. Suppose we have a hierarchy of three classes X, Y, Z in order of inheritance. Y therefore has a base class X and a derived class Z. Now we can define a member function pointer p for class Y. This is written as: void (Y::*p)(); (For simplicity, I'll assume we're only interested in functions with the signature void f() ) This pointer p can now be used to point to member functions of class Y. This question (two questions, really) is then: Can p be used to point to a function in the derived class Z? Can p be used to point to a function in the base class X?

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  • C#: why have all static methods/variables in a non-static class?

    - by Craig Johnston
    I have come across a class which is non-static, but all the methods and variables are static. Eg: public class Class1 { private static string String1 = "one"; private static string String2 = "two"; public static void PrintStrings(string str1, string str2) { ... All the variables are static across all instances, so there is no point having separate instances of the class. Is there any reason to create a class such as this?

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  • Partial class or "chained inheritance"

    - by Charlie boy
    Hi From my understanding partial classes are a bit frowned upon by professional developers, but I've come over a bit of an issue; I have made an implementation of the RichTextBox control that uses user32.dll calls for faster editing of large texts. That results in quite a bit of code. Then I added spellchecking capabilities to the control, this was made in another class inheriting RichTextBox control as well. That also makes up a bit of code. These two functionalities are quite separate but I would like them to be merged so that I can drop one control on my form that has both fast editing capabilities and spellchecking built in. I feel that simply adding the code form one class to the other would result in a too large code file, especially since there are two very distinct areas of functionality, so I seem to need another approach. Now to my question; To merge these two classes should I make the spellchecking RichTextBox inherit from the fast edit one, that in turn inherits RichTextBox? Or should I make the two classes partials of a single class and thus making them more “equal” so to speak? This is more of a question of OO principles and exercise on my part than me trying to reinvent the wheel, I know there are plenty of good text editing controls out there. But this is just a hobby for me and I just want to know how this kind of solution would be managed by a professional. Thanks!

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  • Is it poor design to create objects that only execute code during the constructor?

    - by Curtix
    In my design I am using objects that evaluate a data record. The constructor is called with the data record and type of evaluation as parameters and then the constructor calls all of the object's code necessary to evaluate the record. This includes using the type of evaluation to find additional parameter-like data in a text file. There are in the neighborhood of 250 unique evaluation types that use the same or similar code and unique parameters coming from the text file. Some of these evaluations use different code so I benefit a lot from this model because I can use inheritance and polymorphism. Once the object is created there isn't any need to execute additional code on the object (at least for now) and it is used more like a struct; its kept on a list and 3 properties are used later. I think this design is the easiest to understand, code, and read. A logical alternative I guess would be using functions that return score structs, but you can't inherit from methods so it would make it kind of sloppy imo. I am using vb.net and these classes will be used in an asp.net web app as well as in a distributed app. thanks for your input

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  • Improve this generic abstract class

    - by Keivan
    I have the following abstract class design, I was wondering if anyone can suggest any improvements in terms of stronger enforcement of our requirements or simplifying implementing of the ControllerBase. //Dependency Provider base public abstract class ControllerBase<TContract, TType> where TType : TContract, class { public static TContract Instance { get { return ComponentFactory.GetComponent<TContract, TType>(); } } public TContract GetComponent<TContract, TType>() where TType : TContract, class { component = (TType)Activator.CreateInstance(typeof(TType), true); RegisterComponentInstance<TContract>(component); } } //Contract public interface IController { void DoThing(); } //Actual Class Logic public class Controller: ControllerBase<IController,Controller> { public void DoThing(); //internal constructor internal Controller(){} } //Usage public static void Main() { Controller.Instance.DoThing(); } The following facts should always be true, TType should always implement TContract (Enforced using a generic constraint) TContract must be an interface (Can't find a way to enforce it) TType shouldn't have public constructor, just an internal one, is there any way to Enforce that using ControllerBase? TType must be an concrete class (Didn't include New() as a generic constrain since the constructors should be marked as Internal)

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  • C++ Matrix class hierachy

    - by bpw1621
    Should a matrix software library have a root class (e.g., MatrixBase) from which more specialized (or more constrained) matrix classes (e.g., SparseMatrix, UpperTriangluarMatrix, etc.) derive? If so, should the derived classes be derived publicly/protectively/privately? If not, should they be composed with a implementation class encapsulating common functionality and be otherwise unrelated? Something else? I was having a conversation about this with a software developer colleague (I am not per se) who mentioned that it is a common programming design mistake to derive a more restricted class from a more general one (e.g., he used the example of how it was not a good idea to derive a Circle class from an Ellipse class as similar to the matrix design issue) even when it is true that a SparseMatrix "IS A" MatrixBase. The interface presented by both the base and derived classes should be the same for basic operations; for specialized operations, a derived class would have additional functionality that might not be possible to implement for an arbitrary MatrixBase object. For example, we can compute the cholesky decomposition only for a PositiveDefiniteMatrix class object; however, multiplication by a scalar should work the same way for both the base and derived classes. Also, even if the underlying data storage implementation differs the operator()(int,int) should work as expected for any type of matrix class. I have started looking at a few open-source matrix libraries and it appears like this is kind of a mixed bag (or maybe I'm looking at a mixed bag of libraries). I am planning on helping out with a refactoring of a math library where this has been a point of contention and I'd like to have opinions (that is unless there really is an objective right answer to this question) as to what design philosophy would be best and what are the pros and cons to any reasonable approach.

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  • how can i strip formatting from word document using php

    - by shazia
    I want to display a word file and then extract the content and display it in a separate textarea. i want to do away with the formatting as well. this is what i get when i get the read the text file using php ??????ÿÿÿÿ???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????Running Head: INTERNATIONAL BUSINESS International Business [Name of the writer] [Name of the institution] International Business Question 1 Increasing returns to scale (or economies of scale) in production is an indisputable phenomenon characterizing real world production, and, as such, they have long been recognized as a principal source of economic prosperity. Nonetheless, they have never played a major role in this is the code $fh = fopen($newname, 'r'); $contents => fread($fh, filesize($newname)); fclose($fh); unlink($newname); echo "<br/>"; echo $contents; how can i get rid of all these charecters. Thanks

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  • Do you think functional language is good for applications that have a lot of business rules but very

    - by StackUnderflow
    I am convinced that functional programming is an excellent choice when it comes to applications that require a lot of computation (data mining, AI, nlp etc). But is it wise to use functional programming for a typical enterprise application where there are a lot of business rules but not much in terms of computation? Please disregard the fact that there are very few people using functional programming and that it's kind of tough. Thanks

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  • Using enums or a set of classes when I know I have a finite set of different options?

    - by devoured elysium
    Let's say I have defined the following class: public abstract class Event { public DateTime Time { get; protected set; } protected Event(DateTime time) { Time = time; } } What would you prefer between this: public class AsleepEvent : Event { public AsleepEvent(DateTime time) : base(time) { } } public class AwakeEvent : Event { public AwakeEvent(DateTime time) : base(time) { } } and this: public enum StateEventType { NowAwake, NowAsleep } public class StateEvent : Event { protected StateEventType stateType; public MealEvent(DateTime time, StateEventType stateType) : base(time) { stateType = stateType; } } and why? I am generally more inclined to the first option, but I can't explain why. Is it totally the same or are any advantages in using one instead of the other? Maybe with the first method its easier to add more "states", altough in this case I am 100% sure I will only want two states: now awake, and now asleep (they signal the moments when one awakes and one falls asleep).

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  • Java generics question

    - by user247866
    So I have 3 classes. Abstract class A Class B extends class A independent Class C In class D that contains the main method, I create a list of instances of class B List<B> b = methodCall(); // the method returns a list of instances of class B Now in class C I have one method that is common to both A and B, and hence I don't want to duplicate it. I want to have one method that takes as input an instance of class A, as follows: public void someMethod(List<A> a) However, when I do: C c = new C(); c.someMethod(b); I get an error that some-method is not applicable for the argument List<B>, instead it's expecting to get List<A>. Is there a good way to fix this problem? Many thanks!

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  • How to signal object instantiation in a Collaboration/Communication Diagram?

    - by devoured elysium
    I'd like to know how to translate the following line of code to a Collaboration Diagram: Food food = new Food("abc", 123); I know that I can call an Food's method using the following notation: MyStaticMethod() ----------------------> -------- | | | Food | | | -------- being that equivalent to Taste taste = Food.MyStaticMethod(); and MyInstanceMethod() ----------------------> --------------- | | | food : Food | | | --------------- is equivalent to food.MyInstanceMethod(); but how do I signal that I want to call a given constructor on Food? Thanks

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