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  • Objective C - creating concrete class instances from base class depending upon type

    - by indiantroy
    Just to give a real world example, say the base class is Vehicle and concrete classes are TwoWheeler and FourWheeler. Now the type of the vehicle - TwoWheeler or FourWheeler, is decided by the base class Vehicle. When I create an instance of TwoWheeler/FourWheeler using alloc-init method, it calls the super implementation like below to set the value of common properties defined in the Vehicle class and out of these properties one of them is type that actually decides if the type is TwoWheeler or FourWheeler. if (self = [super initWithDictionary:dict]){ [self setOtherAttributes:dict]; return self; } Now when I get a collection of vehicles some of them could be TwoWheeler and others will be FourWheeler. Hence I cannot directly create an instance of TwoWheeler or FourWheeler like this Vehicle *v = [[TwoWheeler alloc] initWithDictionary:dict]; Is there any way I can create an instance of base class and once I know the type, create an instance of child class depending upon type and return it. With the current implementation, it would result in infinite loop because I call super implementation from concrete class. What would be the perfect design to handle this scenario when I don't know which concrete class should be instantiated beforehand?

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  • javascript : make a new safe class constructor

    - by guilin ??
    sometimes we loss the new keyword when define new object, obj = new Clazz(); //correct obj = Clazz(); //wrong, but no syntax error, hard to debug. I want to write a function to help me create Class and make it new safe. var Class = function(constructor){ //when constructor // if not call by new return new constructor(); // else constructor(); } var MyClazz = Class(function(name){ this.name = name }, SuperClazz1, SuperClass2 ) MyClazz.extend({ show: function(){console.log(this.name)} }) obj1 = new MyClazz(); obj2 = MyClazz(); // obj1 should same as obj2 Is it possible, any exists module?

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  • is "Object();" a predefined function in javascript?

    - by Qlidnaque
    I come across code such as "personObj=new Object();" where a new object called personObj is being defined. What I'm trying to find out is whether Object() is a prefined function in javascript, because I understand by using the mentioned code, a instance of a class is being formed but in the example code where I'm studying from, the class Object() is not being defined anywhere, so I was wondering if Object() was a predefined function in javascript and whether I can be directed to some online resources, as all that shows up in google when I try to find Object() are articles in general javascript object oriented programming.

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  • PHP class extends not working why and is this how to correctly extend a class?

    - by Matthew
    Hi so I'm trying to understand how inherteince works in PHP using object oriented programming. The main class is Computer, the class that is inheriting is Mouse. I'm extedning the Computer class with the mouse class. I use __construct in each class, when I istinate the class I use the pc type first and if it has mouse after. For some reason computer returns null? why is this? class Computer { protected $type = 'null'; public function __construct($type) { $this->type = $type; } public function computertype() { $this->type = strtoupper($this->type); return $this->type; } } class Mouse extends Computer { protected $hasmouse = 'null'; public function __construct($hasmouse){ $this->hasmouse = $hasmouse; } public function computermouse() { if($this->hasmouse == 'Y') { return 'This Computer has a mouse'; } } } $pc = new Computer('PC', 'Y'); echo $pc->computertype; echo $pc->computermouse;

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  • Three customer addresses in one table or in separate tables?

    - by DR
    In my application I have a Customer class and an Address class. The Customer class has three instances of the Address class: customerAddress, deliveryAddress, invoiceAddress. Whats the best way to reflect this structure in a database? The straightforward way would be a customer table and a separate address table. A more denormalized way would be just a customer table with columns for every address (Example for "street": customer_street, delivery_street, invoice_street) What are your experiences with that? Are there any advantages and disadvantages of these approaches?

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  • private classes inside namespaces

    - by blacklion
    Is there a way to restrict access to a class from outside a namespace? What I want is to have a class that is only accessible to other classes inside the same namespace without having to put the namespace in it's own assembly. Is there a reason this is not possible in C#?

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  • An issue on object orientation in php

    - by rabidmachine9
    Hello people, I have come up to issues while I'm trying to write some classes, here is an example: I have this class called TwitterGrub and I cant call it like that: $c = new TwitterGrub(); $c->twitterDisplay(); here is the class itself: <?php class TwitterGrub{ function twitterCapture($user = 'username',$password = 'pass') { $ch = curl_init("https://twitter.com/statuses/user_timeline.xml"); curl_setopt($ch, CURLOPT_HEADER, 1); curl_setopt($ch,CURLOPT_TIMEOUT, 30); curl_setopt($ch,CURLOPT_USERPWD,$user . ":" . $password); curl_setopt($ch,CURLOPT_RETURNTRANSFER,1); curl_setopt ($ch, CURLOPT_SSL_VERIFYPEER, 0); curl_setopt ($ch, CURLOPT_SSL_VERIFYHOST, 0); $result=curl_exec ($ch); $data = strstr($result, '<?'); $xml = new SimpleXMLElement($data); return $xml; } function twitterDisplay($twitNum = 2){ $xml = $this::twitterCapture(); for($i= 0; $i<$twitNum; $i++){ echo "<div class= 'curvebox'>".$xml->status[$i]->text."</div>"; } } } ?> The problem is that everytime I want to change the username or password I have to jump back to class definition and that makes things not modular... and in many ways it feels wrong. So the question is what would be the proper way to chance my username and password through the objects interface and then call twitterDisplay() method with the new data?Hope that makes sense. Thanks in advance

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  • How to manage member variable in C++

    - by rhapsodyn
    In brief, my question is about member variables as pointers in unmanaged C++. In java or c#, we have "advanced pointer". In fact, we can't aware the "pointer" in them. We usually initialize the member of a class like this: member = new Member(); or member = null; But in c++, it becomes more confusing. I have seen many styles: using new, or leave the member variable in stack. In my point of view, using boost::shared_ptr seems friendly, but in boost itself source code there are news everywhere. It's the matter of efficiency,isn't it? Is there a guildline like "try your best to avoid new" or something?

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  • Javascript plugin creation

    - by Aneesh
    I want to create a plugin called 'myPlugin'. Which method should I use and what is the difference between these two methods? Please tell me the advantages too. I am from designing background and not much programming knowledge. var myPlugin = { myId:"testId", create:function(){}, destroy:function(){} } OR function myPlugin() { this.myId = "testId"; this.create = function(){}; this.destroy = function(){}; }

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  • Do you use Python mostly for its functional or object-oriented features?

    - by Eric
    I see what seems like a majority of Python developers on StackOverflow endorsing the use of concise functional tools like lambdas, maps, filters, etc., while others say their code is clearer and more maintainable by not using them. What is your preference? Also, if you are a die-hard functional programmer or hardcore into OO, what other specific programming practices do you use that you think are best for your style? Thanks in advance for your opinions!

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  • Designing operation (a,b) -> (c,d)

    - by golergka
    I have an operation that I need to design. That operation takes two objects of a certain class X, and returns two new objects of the same class (I may need the originals later). The logic that dictates the selection of this object is contained in class Y. On one hand, I don't want class Y to know details about class X implementation; on the other, I don't want class X to know details about selecting the different objects to perform this operation on. If that was all the problem, I'd just create a static method on class A. However, the methods in language I'm working on return only one object. Also, the operation needs to be robust, and calling operation two times to get C and D respectively isn't possible, as both C & D both rely on a single random number. How should I design such operation? Update: I'm using Obejctive C.

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  • interface abstract in php real world scenario

    - by jason
    The goal is to learn whether to use abstract or interface or both... I'm designing a program which allows a user to de-duplicate all images but in the process rather then I just build classes I'd like to build a set of libraries that will allow me to re-use the code for other possible future purposes. In doing so I would like to learn interface vs abstract and was hoping someone could give me input into using either. Here is what the current program will do: recursive scan directory for all files determine file type is image type compare md5 checksum against all other files found and only keep the ones which are not duplicates Store total duplicates found at the end and display size taken up Copy files that are not duplicates into folder by date example Year, Month folder with filename is file creation date. While I could just create a bunch of classes I'd like to start learning more on interfaces and abstraction in php. So if I take the scan directory class as the first example I have several methods... ScanForFiles($path) FindMD5Checksum() FindAllImageTypes() getFileList() The scanForFiles could be public to allow anyone to access it and it stores in an object the entire directory list of files found and many details about them. example extension, size, filename, path, etc... The FindMD5Checksum runs against the fileList object created from scanForFiles and adds the md5 if needed. The FindAllImageTypes runs against the fileList object as well and adds if they are image types. The findmd5checksum and findallimagetypes are optionally run methods because the user might not intend to run these all the time or at all. The getFileList returns the fileList object itself. While I have a working copy I've revamped it a few times trying to figure out whether I need to go with an interface or abstract or both. I'd like to know how an expert OO developer would design it and why?

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  • Why this doesnt't work in C++?

    - by user3377450
    I'm doing something and I have this: //main.cpp file template<typename t1, typename t2> std::ostream& operator<<(std::ostream& os, const std::pair<t1, t2>& pair) { return os << "< " << pair.first << " , " << pair.second << " >"; } int main() { std::map<int, int> map = { { 1, 2 }, { 2, 3 } }; std::cout << *map.begin() << std::endl;//This works std::copy(map.begin(), map.end(), std::ostream_iterator<std::pair<int,int> >(std::cout, " "));//this doesn't work } I guess this is not working because in the std::copy algorithm the operator isn't defined, but what can I do?

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  • Creating instance of interface in C#

    - by Max
    I'm working with MS Excel interop in C# and I don't understand how this particular line of code works: var excel = new Microsoft.Office.Interop.Excel.Application(); where Microsoft.Office.Interop.Excel.Application is an INTERFACE defined as: [Guid("000208D5-0000-0000-C000-000000000046")] [CoClass(typeof(ApplicationClass))] public interface Application : _Application, AppEvents_Event { } I'm thinking that some magic happens when the interface is decorated with a CoClass attribute, but still how is it possible that we can create an instance of an interface with a new keyword? Shouldn't it generate a compile time error?

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  • Struct like objects in Java

    - by cdv
    Is it completely against the Java way to create struct like objects? class SomeData1 { public int x; public int y; } I can see a class with accessors and mutators being more Java like. class SomeData2 { int getX(); void setX(int x); int getY(); void setY(int y); private int x; private int y; } The class from the first example is notationally convenient. // a function in a class public int f(SomeData1 d) { return (3 * d.x) / d.y; } This is not as convenient. // a function in a class public int f(SomeData2 d) { return (3 * d.getX()) / d.getY(); }

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  • Is it possible for an abstract class to force it's children to have a constructor in PHP?

    - by Logan Serman
    I would like to do something like this: abstract class Foo { public function __construct() { echo 'This is the parent constructor'; } abstract function __construct(); } class Bar extends Foo { // constructor is required as this class extends Foo public function __construct() { //call parent::__construct() if necessary echo 'This is the child constructor'; } } But I get a fatal error when doing this: Fatal error: Cannot redeclare Foo::__construct() in Foo.php on line 8 Is there another way to ensure child classes have a constructor?

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  • PHP object cannot find method

    - by Daniel Hertz
    Hello, So I have a very simple class that has a method called getThumbUrl() but when I try calling this method on an instance I get Notice: Undefined property: FlickrImage::$getFullUrl But it is clearly there. Here is the code of the function: public function getThumbUrl() { return "http://farm".$this->_farm.".static.flickr.com/".$this->_server."/".$this->_id."_".$this->_secret."_t.jpg"; } And here is where it fails: foreach($photos as $photo) { echo "<img src='$photo->getFullUrl()' />"; } Any ideas? Thanks!

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  • Can a problem have a relation of aggregation and composition both between two classes at same point

    - by learner
    Can a problem have a relation of aggregation and composition both between two classes at same point of time? Like any real time scenario where there can be aggregation corresponding to one method and composition related to other method. I m unable to figure out any scenario where both composition and aggregation occurs simultaneously between two classes. Any help will be appreciable.

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  • A self-creator: What pattern is this? php

    - by user151841
    I have several classes that are basically interfaces to database rows. Since the class assumes that a row already exists ( __construct expects a field value ), there is a public static function that allows creation of the row and returns an instance of the class. Here's a pseudo-code example : class fruit { public $id; public function __construct( $id ) { $this->id = $id; $sql = "SELECT * FROM Fruits WHERE id = $id"; ... $this->arrFieldValues[$field] = $row[$value]; } public function __get( $var ) { return $this->arrFieldValues[$var]; } public function __set( $var, $val ) { $sql = "UPDATE fruits SET $var = $val WHERE id = $this->id"; } public static function create( $id ) { $sql = "INSERT INTO Fruits ( fruit_name ) VALUE ( '$fruit' )"; $id = mysql_insert_id(); $fruit = & new fruit($id); return $fruit; } } $obj1 = fruit::create( "apple" ); $obj2 = & new fruit( 12 ); What is this pattern called? Edit: I changed the example to one that has more database-interface functionality. For most of the time, this kind of class would be instantiated normally, through __construct(). But sometimes when you need to create a new row first, you would call create().

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  • self-destructing objects in php5?

    - by user151841
    I am working on a class in php that is basically an interface to a database row. I wanted to create a delete() method that would 1. delete the database row and 2. destroy the instance of itself so that further attempts to manipulate the row via the object would throw warnings. Doing some googling, it seems that, in php5, it's not possible for an object to unset itself. http://bugs.php.net/bug.php?id=36971 In fact they discuss the very situation I was wanting to do :( So how should I proceed? I could make boolean flag as a class property, for whether the row still exists, and have each operation check that flag and throw an error if the row has been deleted. This maintains the oo structure of code, so I would have $objDbRow->delete(); But then I have to put checks at the beginning of each method. Or, I could implement a __destruct method that deletes the row. But that would seem counter-intuitive to me; if I saw in code unset($objDbRow); All I would suspect that's happening is that the object is being discarded, not that a row is being deleted. So that to me would seem like bad practice.

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