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  • When do you use metaclasses?

    - by johannix
    Just started looking into metaclasses and while they seem powerful, I can think of other ways to accomplish the same type of thing. I was wondering when metaclasses have been found to be the right answer and why.

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  • How to "wrap" implementation in C#

    - by igor
    Hello, I have these classes in C# (.NET Framework 3.5) described below: public class Base { public int State {get; set;} public virtual int Method1(){} public virtual string Method2(){} ... public virtual void Method10(){} } public class B: Base { // some implementation } public class Proxy: Base { private B _b; public class Proxy(B b) { _b = b; } public override int Method1() { if (State == Running) return _b.Method1(); else return base.Method1(); } public override string Method2() { if (State == Running) return _b.Method2(); else return base.Method2(); } public override void Method10() { if (State == Running) _b.Method10(); else base.Method10(); } } I want to get something this: public Base GetStateDependentImplementation() { if (State == Running) // may be some other rule return _b; else return base; // compile error } and my Proxy's implementation will be: public class Proxy: Base { ... public override int Method1() { return GetStateDependentImplementation().Method1(); } public override string Method2() { return GetStateDependentImplementation().Method2(); } ... } Of course, I can do this (aggregation of base implementation): public RepeaterOfBase: Base // no any overrides, just inheritance { } public class Proxy: Base { private B _b; private RepeaterOfBase _Base; public class Proxy(B b, RepeaterOfBase aBase) { _b = b; _base = aBase; } } ... public Base GetStateDependentImplementation() { if (State == Running) return _b; else return _Base; } ... But instance of Base class is very huge and I have to avoid to have other additional copy in memory. So I have to simplify my code have to "wrap" implementation have to avoid a code duplication have to avoid aggregation of any additional instance of Base class (duplication) Is it possible to reach these goals?

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  • C# Design a class with interface?

    - by Haroon
    I am having a bit of trouble understanding how I will design a class. My class will have 3 methods ICollection<Field> GetFields(); //perform validation internally - return back the object T UpdateFields(ICollection<Field> fields); //pass in model object with values on it, set up fields, then pass back all fields ICollection<Field> GetFieldsWithValues(T object); What is the best way to construct/design such a class keeping in mind: 1. The model object I pass in will be one of 3 or 4 tables, however when I call GetFIelds - internally for each object I know what fields will be there i.e. list.add(new Field{name = "id", value = "5"}); list.add(new Field{name = "nameofcompany", value = "super guys"});

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  • Manually setting object's position or have the object do it all?

    - by N. Lucas
    I'm stuck thinking about the best way to go about setting a line segment's position, I have a class Line(length, angle, previous) being called from a class Polygon.. Right now I have: public function Line(length:Number, angle:Number, previous:Line = null) { if (previous != null) { this.x = previous.end.x; this.y = previous.end.y; } /**/ } Now, is this the best practice or should I be doing: Polygon.addLine(length:Number, angle:Number):void { var previous = _line[_line.length - 1]; // Array containing all Lines var line:Line = new Line(length, angle, previous); line.x = previous.end.x; line.y = previous.end.y; /**/ }

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  • Objects instead of global variables in Perl

    - by Gaurav Dadhania
    I don't know if this is the right thing to do. But I'm lookig for tutorials/articles on using objects instead of global variables to store state. For eg. package something # some code here... # that generates errors and uses # something::errors to track errors. package something::errors sub new { my ($this) = @_; bless $this; return $this; } sub setErrors{ my ($this, @errors) = @_; $this->{errors} = \@errors; } sub getErrors{ my ($this) = @_; return $this->{errors}; } Is this better than using global varibles? Any down-sides to this? Any approach which might be better? Thanks.

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  • Is it possible to create nested classes in PHP as it is in C#?

    - by Edward Tanguay
    In C# you can have nested classes like this, which are useful if you have classes which do not have meaning outside the scope of one particular class, e.g. in a factory pattern: public abstract class BankAccount { private BankAccount() {} private sealed class SavingsAccount : BankAccount { ... } private sealed class CheckingAccount : BankAccount { ... } public BankAccount MakeSavingAccount() { ... } public BankAccount MakeCheckingAccount() { ... } } Is this possible in PHP? I've read that it was planned for PHP 5, then cancelled, then planned again, but can't find definitive info. Does anyone know how to create nested classes (classes within the scope of another class) as in the above C# example using PHP 5.3?

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  • Interview question: difference between object and object-oriented languages.

    - by Bar
    My friend was asked the following question: what's the difference between object language and object-oriented language? It's a little unintelligible question. What does term «object language» correspond to? Does that mean «pure» object-oriented language, like the Wikipedia article says: Languages called "pure" OO languages, because everything in them is treated consistently as an object, from primitives such as characters and punctuation, all the way up to whole classes, prototypes, blocks, modules, etc. They were designed specifically to facilitate, even enforce, OO methods. Examples: Smalltalk, Eiffel, Ruby, JADE, VB.NET.

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  • What's the benefit of calling new on an object instance?

    - by Geo
    I'm reading [Programming Perl][1], and I found this code snippet: sub new { my $invocant = shift; my $class = ref($invocant) || $invocant; my $self = { color => "bay", legs => 4, owner => undef, @_, # Override previous attributes }; return bless $self, $class; } With constructors like this one, what's the benefit of calling new on an object instance? I assume that it's what it's for, right? My guess is that if anyone would want to write such a constructor, he would have to add some more code that copies the attributes of the first object to the one about to be created.

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  • Javascript Instance Variable Syntax (AJAX page refresh)

    - by Rosarch
    I'm having difficulty with Javascript instance variables. I'm trying to make an easy way to refresh the chat page, looking for new messages. The AJAX call supplies a mid, or the lowest message id to be returned. This allows the call to only ask for the most recent messages, instead of all of them. MessageRefresher.prototype._latest_mid; function MessageRefresher(latest_mid) { this._latest_mid = latest_mid; // it thinks `this` refers to the MessageRefresher object } MessageRefresher.prototype.refresh = function () { refreshMessages(this._latest_mid); // it thinks `this` refers to the window this._latest_mid++; } function refreshMessages(latest_mid) { $.getJSON('API/read_messages', { room_id: $.getUrlVar('key'), mid: latest_mid }, function (messages) { for (var i = 0; i < messages[0].length; i++) { var newChild = sprintf("<li>%s: %s</li>", messages[1][i], messages[0][i]); $("#messages").append(newChild); } }); var messageRefresher = new MessageRefresher(0); setInterval(messageRefresher.refresh, 1000); This results in all the messages being printed out, over and over again. I know it has other bugs, but the main issue I'm trying to work out right now is the use of the instance variable. Or is there another way I should be going about doing this?

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  • How should I organize my C# classes? [closed]

    - by oscar.fimbres
    I'm creating an email generator system. I'm creating some clases and I'm trying to make things right. By the time, I have created 5 classes. Look at the class diagram: I'm going to explain you each one. Person. It's not a big deal. Just have two constructors: Person(fname, lname1, lname2) and Person(token, fname, lname1, lname2). Note that email property stays without value. StringGenerator. This is a static class and it has only a public function: Generate. The function receives a Person class and it will return a list of patterns for the email. MySql. It contains all the necessary to connect to a database. Database. This class inherits from MySql class. It has particular functions for the database. This gets all the registries from a table (function GetPeople) and return a List. Each person from the list contains all data except Email. Also it can add records (List but this must contains an available email). An available email is when an email doesn't have another person. For that reason, I have a method named ExistsEmail. Container. This is the class which is causing me some problems. It's like a temporary container. It supposed to have a people list from GetPeople (in Database class) and for each person it adds, it must generate a list of possible names (StringGenerator.Generate), then it selects one of the list and it must check out if exists in the database or in the same container. As I told above this is temporal, it may none of the possible emails is available. So the user can modify or enter a custom email available and update the list in this container. When all the email's people are available, it sends a list to add in the database, It must have a Flush method, to insert all the people in the database. I'm trying to design correct class. I need a little help to improve or edite the classes, because I want to separate the logic and visual, and learn of you. I hope you've been able to understand me. Any question or doubt, please let me know. Anyway, I attached the solution here to better understand it: http://www.megaupload.com/?d=D94FH8GZ

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  • 'is instanceof' Interface bad design

    - by peterRit
    Say I have a class A class A { Z source; } Now, the context tells me that 'Z' can be an instance of different classes (say, B and C) which doesn't share any common class in their inheritance tree. I guess the naive approach is to make 'Z' an Interface class, and make classes B and C implement it. But something still doesn't convince me because every time an instance of class A is used, I need to know the type of 'source'. So all finishes in multiple 'ifs' making 'is instanceof' which doesn't sound quite nice. Maybe in the future some other class implements Z, and having hardcoded 'ifs' of this type definitely could break something. The escence of the problem is that I cannot resolve the issue by adding functions to Z, because the work done in each instance type of Z is different. I hope someone can give me and advice, maybe about some useful design pattern. Thanks

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  • Can I have two names for the same variable?

    - by Roman
    The short version of the question: I do: x = y. Then I change x, and y is unchanged. What I want is to "bind" x and y in such a way that I change y whenever I change x. The extended version (with some details): I wrote a class ("first" class) which generates objects of another class ("second" class). In more details, every object of the second class has a name as a unique identifier. I call a static method of the first class with a name of the object from the second class. The first class checks if such an object was already generated (if it is present in the static HashMap of the first class). If it is already there, it is returned. If it is not yet there, it is created, added to the HashMap and returned. And then I have the following problem. At some stage of my program, I take an object with a specific name from the HashMap of the first class. I do something with this object (for example change values of some fields). But the object in the HashMap does not see these changes! So, in fact, I do not "take" an object from the HashMap, I "create a copy" of this object and this is what I would like to avoid.

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  • Using the same modules in multiple projects

    - by Andreas Vinther
    I'm using Visual Studio 2010 and coding in VB.NET. My problem is that I've collected all the modules I've written and intend to reuse and placed them in a separate folder. When I want to add a module from the above folder to any given project, it takes a copy of the module and places in the project's source code folder, instead of referencing the module in the folder containing all the other modules. Is it possible to include a module in my project and leave it in the folder with all the other modules, so that when I improve upon a module, it'll affect all the projects that uses/references that module. Instead of me having to manually copy the new module to all the projects that uses/references the module. Right now I have multiple instances of the exact same module that i need to update manually when I improve code or add functionality?

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  • C++ (g++) Compile Error, Expected "="/etc. Before 'MyWindow" (my class name)

    - by Ell
    Hi all, I have a very strange problem and the following code wont compile: #ifndef MYWINDOW_HPP_INCLUDED #define MYWINDOW_HPP_INCLUDED class MyWindow{ private: WNDCLASSEX window_class; HWND window_handle; HDC device_context_handle; HGLRC open_gl_render_context; MSG message; BOOL quit; public: Window(int height=416, int width=544, WindowStyle window_style=WINDOWED); void Show(); void Close(); ~Window(); }; #endif // MYWINDOW_HPP_INCLUDED I get the following error: error: expected '=', ',', ';', 'asm' or 'attribute' before 'MyWindow' I can't see any syntax errors here, although I coukd be wrong as I am very (very) new in c++. Thanks in advance, ell.

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  • Not very objective - please help

    - by chainwork
    I am having trouble understanding the meaning and more importantly the concept of an object as it relates to jQuery. I understand the basics that its a collection of data that comes in two forms, properties and methods but I kind of get lost on how it works beyond that. Can anyone point me to some good tutorials that maybe helped you understand? I'm hoping to "Get it" once and for all. Many many thanks for your help! =]

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  • Exposing members or make them private in Python?

    - by deamon
    Is there a general convention about exposing members in Python classes? I know that this is a case of "it depends", but maybe there is a rule of thumb. Private member: class Node: def __init__(self): self.__childs = [] def add_childs(self, *args): self.__childs += args node = Node() node.add_childs("one", "two") Public member: class Node2: def __init__(self): self.childs = [] node2 = Node2() node2.childs += "one", "two"

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  • Passing parameter to base class constructor or using instance variable?

    - by deamon
    All classes derived from a certain base class have to define an attribute called "path". In the sense of duck typing I could rely upon definition in the subclasses: class Base: pass # no "path" variable here def Sub(Base): def __init__(self): self.path = "something/" Another possiblity would be to use the base class constructor: class Base: def __init__(self, path): self.path = path def Sub(Base): def __init__(self): super().__init__("something/") What would you prefer and why? Is there a better way?

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  • Best way to track the stages of a form across different controllers - $_GET or routing

    - by chrisj
    Hi, I am in a bit of a dilemma about how best to handle the following situation. I have a long registration process on a site, where there are around 10 form sections to fill in. Some of these forms relate specifically to the user and their own personal data, while most of them relate to the user's pets - my current set up handles user specific forms in a User_Controller (e.g via methods like user/profile, user/household etc), and similarly the pet related forms are handled in a Pet_Controller (e.g pet/health). Whether or not all of these methods should be combined into a single Registration_Controller, I'm not sure - I'm open to any advice on that. Anyway, my main issue is that I want to generate a progress bar which shows how far along in the registration process each user is. As the urls in each form section can potentially be mapping to different controllers, I'm trying to find a clean way to extract which stage a person is at in the overall process. I could just use the query string to pass a stage parameter with each request, e.g user/profile?stage=1. Another way to do it potentially is to use routing - e.g the urls for each section of the form could be set up to be registration/stage/1, registration/stage/2 - then i could just map these urls to the appropriate controller/method behind the scenes. If this makes any sense at all, does anyone have any advice for me?

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  • How do I write object classes effectively when dealing with table joins?

    - by Chris
    I should start by saying I'm not now, nor do I have any delusions I'll ever be a professional programmer so most of my skills have been learned from experience very much as a hobby. I learned PHP as it seemed a good simple introduction in certain areas and it allowed me to design simple web applications. When I learned about objects, classes etc the tutor's basic examnples covered the idea that as a rule of thumb each database table should have its own class. While that worked well for the photo gallery project we wrote, as it had very simple mysql queries, it's not working so well now my projects are getting more complex. If I require data from two separate tables which require a table join I've instead been ignoring the class altogether and handling it on a case by case basis, OR, even worse been combining some of the data into the class and the rest as a separate entity and doing two queries, which to me seems inefficient. As an example, when viewing content on a forum I wrote, if you view a thread, I retrieve data from the threads table, the posts table and the user table. The queries from the user and posts table are retrieved via a join and not instantiated as an object, whereas the thread data is called using my Threads class. So how do I get from my current state of affairs to something a little less 'stupid', for want of a better word. Right now I have a DB class that deals with connection and escaping values etc, a parent db query class that deals with the common queries and methods, and all of the other classes (Thread, Upload, Session, Photo and ones thats aren't used Post, User etc ) are children of that. Do I make a big posts class that has the relevant extra attributes that I retrieve from the users (and potentially threads) table? Do I have separate classes that populate each of their relevant attributes with a single query? If so how do I do that? Because of the way my classes are written, based on what I was taught, my db update row method, or insert method both just take the attributes as an array and update all of that, if I have extra attributes from other db tables in each class then how do I rewrite those methods as obbiously updating automatically like that would result in errors? In short I think my understanding is limited right now and I'd like some pointers when it comes to the fundamentals of how to write more complex classes.

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  • Factory vs instance constructors

    - by Neil N
    I can't think of any reasons why one is better than the other. Compare these two implementations: public class MyClass { public myClass(string fileName) { // some code... } } as opposed to: public class MyClass { private myClass(){} public static Create(string fileName) { // some code... } } There are some places in the .Net framework that use the static method to create instances. At first I was thinking, it registers it's instances to keep track of them, but regular constructors could do the same thing through the use of private static variables. What is the reasoning behind this style?

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  • Override java methods without affecting parent behaviour

    - by Timmmm
    suppose I have this classes (sorry it's kind of hard to think of a simple example here; I don't want any "why would you want to do that?" answers!): class Squarer { public void setValue(int v) { mV = v; } public int getValue() { return mV; } private int mV; public void square() { setValue(getValue() * getValue()); } } class OnlyOddInputsSquarer extends Squarer { @Override public void setValue(int v) { if (v % 2 == 0) { print("Sorry, this class only lets you square odd numbers!") return; } super.setValue(v); } } auto s = new OnlyOddInputsSquarer(); s.setValue(3); s.square(); This won't work. When Squarer.square() calls setValue(), it will go to OnlyOddInputsSquarer.setValue() which will reject all its values (since all squares are even). Is there any way I can override setValue() so that all the functions in Squarer still use the method defined there? PS: Sorry, java doesn't have an auto keyword you haven't heard about! Wishful thinking on my part.

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  • How do I change the URL Alias for Security/login in SilverStripe to user/login

    - by pthurmond
    I am working on a new website being built in SilverStripe. Currently I am having a ton of trouble trying to get the system to let me change the URL alias (or create a second one) for the Security controller's login (and eventually logout) function. I have tried playing around with the routes.yml file and I tried creating the paths in my own UserController and loading directly from the Security controller with "return Security::login()". But that gives me errors about the use of the static functions. Unfortunately I don't come from a ton of object oriented experience and this is the first CMS I have used that actually uses a bunch of true object orientation. The current version of SilverStripe we are using is 3.0 (but we will be upgrading to 3.1.1 in a few days). Does anyone know much about the routing in SilverStripe?

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  • design patterns for hierarchical structures

    - by JLBarros
    Anyone knows some design patterns for hierarchical structures? For example, to manage inventory categories, accounting chart of accounts, divisions of human resources, etc.. Thank you very much in advance EDIT: Thanks for your interest. I am looking for a better way of dealing with hierarchical items to which they should apply operations depending on the level of hierarchy. I have been studying the patterns by Martin Fowler, for example Accounting, but I wonder if there are other more generic. The problem is that operations apply to the items must be possible to change even at run time and may depend on other external variables. I thought of a kind of strategy pattern but would like to combine it with the fact that it is a hierarchical scheme. I would appreciate any reference to hierarchical patterns and you'll take care of them in depth.

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