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  • Monad in plain English? (For the OOP programmer with no FP background)

    - by fig-gnuton
    In terms that an OOP programmer would understand (without any functional programming background), what is a monad? What problem does it solve and what are the most common places it's used? EDIT: To clarify the kind of understanding I was looking for, let's say you were converting an FP application that had monads into an OOP application. What would you do to port the responsibilities of the monads into the OOP app?

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  • How did you get good practices for your OOP designs?

    - by Darf Zon
    I realized I have a difficulty creating OOP designs. I spent many time deciding if this property is correctly set it to X class. For example, this is a post which has a few days: http://codereview.stackexchange.com/questions/8041/how-to-improve-my-factory-design I'm not convinced of my code. So I want to improve my designs, take less time creating it. How did you learn creating good designs? Some books that you can recommend me?

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  • Language Agnostic Basic Programming Question

    - by Rachel
    This is very basic question from programming point of view but as I am in learning phase, I thought I would better ask this question rather than having a misunderstanding or narrow knowledge about the topic. So do excuse me if somehow I mess it up. Question: Let's say I have class A,B,C and D now class A has some piece of code which I need to have in class B,C and D so I am extending class A in class B, class C, and class D Now how can I access the function of class A in other classes, do I need to create an object of class A and than access the function of class A or as am extending A in other classes than I can internally call the function using this parameter. If possible I would really appreciate if someone can explain this concept with code sample explaining how the logic flows. Note Example in Java, PHP and .Net would be appreciated.

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  • Object Oriented PHP Best Practices

    - by user270797
    Say I have a class which represents a person, a variable within that class would be $name. Previously, In my scripts I would create an instance of the object then set the name by just using: $object->name = "x"; However, I was told this was not best practice? That I should have a function set_name() or something similar like this: function set_name($name) { $this->name=$name; } is this correct? If in this example I want to insert a new "person" record into the db, how do I pass all the information about the person ie $name, $age, $address, $phone etc to the class in order to insert it, should I do: function set($data) { $this->name= $data['name']; $this->age = $data['age']; etc etc } Then send it an array? Would this be best practice? or could someone please recommend best practice?

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  • OO Design - polymorphism - how to design for handing streams of different file types

    - by Kache4
    I've little experience with advanced OO practices, and I want to design this properly as an exercise. I'm thinking of implementing the following, and I'm asking if I'm going about this the right way. I have a class PImage that holds the raw data and some information I need for an image file. Its header is currently something like this: #include <boost/filesytem.hpp> #include <vector> namespace fs = boost::filesystem; class PImage { public: PImage(const fs::path& path, const unsigned char* buffer, int bufferLen); const vector<char> data() const { return data_; } const char* rawData() const { return &data_[0]; } /*** other assorted accessors ***/ private: fs::path path_; int width_; int height_; int filesize_; vector<char> data_; } I want to fill the width_ and height_ by looking through the file's header. The trivial/inelegant solution would be to have a lot of messy control flow that identifies the type of image file (.gif, .jpg, .png, etc) and then parse the header accordingly. Instead of using vector<char> data_, I was thinking of having PImage use a class, RawImageStream data_ that inherits from vector<char>. Each type of file I plan to support would then inherit from RawImageStream, e.g. RawGifStream, RawPngStream. Each RawXYZStream would encapsulate the respective header-parsing functions, and PImage would only have to do something like height_ = data_.getHeight();. Am I thinking this through correctly? How would I create the proper RawImageStream subclass for data_ to be in the PImage ctor? Is this where I could use an object factory? Anything I'm forgetting?

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  • Usabe of Python 3 super()

    - by deamon
    I wonder when to use what flavour of Python 3 super(). Help on class super in module builtins: class super(object) | super() -> same as super(__class__, <first argument>) | super(type) -> unbound super object | super(type, obj) -> bound super object; requires isinstance(obj, type) | super(type, type2) -> bound super object; requires issubclass(type2, type) Until now I've used super() only without arguments and it worked as expected (by a Java developer). Questions: What does "bound" mean in this context? What is the difference between bound and unbound super object? When to use super(type, obj) and when super(type, type2)? Would it be better to name the super class like in Mother.__init__(...)?

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  • R: Pass by reference

    - by Pierre
    Can you pass by reference with "R" ? for example, in the following code: setClass("MyClass", representation( name="character" )) instance1 <-new("MyClass",name="Hello1") instance2 <-new("MyClass",name="Hello2") array = c(instance1,instance2) instance1 array instance1@name="World!" instance1 array the output is > instance1 An object of class “MyClass” Slot "name": [1] "World!" > array [[1]] An object of class “MyClass” Slot "name": [1] "Hello1" [[2]] An object of class “MyClass” Slot "name": [1] "Hello2" but I wish it was > instance1 An object of class “MyClass” Slot "name": [1] "World!" > array [[1]] An object of class “MyClass” Slot "name": [1] "World!" [[2]] An object of class “MyClass” Slot "name": [1] "Hello2" is it possible ? Thanks Pierre

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  • Having trouble with instantiating objects in PHP & Ajax custom shopping cart

    - by Phil
    This is my first time playing with both ajax and objects, so please go easy on me I have 3 pages that make up the tester shopping cart. 1) page with 'add' 'remove' buttons and ajax code to call the PHP functions on page 2. this is the actual user page with the HTML output. 2) page with PHP cart function calls, receives $_GET requests from ajax on page 1 and calls functions of the cart object from page 3, returns results to page 1. 3) page with cart object definition. Here's the problem I believe I'm having. Currently I have 'session_start()' on pgs 1 & 2, and the cart definition (pag 3) on pgs 1 & 2. I only define '$_SESSION[cart]= new Cart' on page 2. However, it seems like each time i hit an ajax function (eg each time pg 2 reloads) it seems like it's rewriting $_SESSION['cart'] over again, thus it's always empty at each new click (even tho it displays results of that click) However, if i don't define '$_SESSION[cart] = new Cart' on pg 2, i get an error: Fatal error: main() [function.main]: The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "Cart" of the object you are trying to operate on was loaded before unserialize() gets called or provide a __autoload() function to load the class definition in /home3/foundloc/public_html/booka/carti.php on line 17 Any suggestions? How can i stop re-creating my cart each time my page 2 (php cart function page) is called by ajax?

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  • How to correctly refactor this?

    - by kane77
    I have trouble finding way to correctly refactor this code so that there would be as little duplicate code as possible, I have a couple of methods like this (pseudocode): public List<Something> parseSomething(Node n){ List<Something> somethings = new ArrayList<Something>(); initialize(); sameCodeInBothClasses(); List<Node> nodes = getChildrenByName(n, "somename"); for(Node n:nodes){ method(); actionA(); somethings.add(new Something(actionB()); } return somethings; } methods sameCodeInBothClasses() are same in all classes but where it differs is what hapens in for loop actionA() and it also adds an element to the List of different type. Should I use Strategy pattern for the different parts inside loop? What about the return value (The type of list differs), should the method return just List<Object> that I would then cast to appropriate type? Should I pass the class I want to return as parameter?

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  • Usage of Python 3 super()

    - by deamon
    I wonder when to use what flavour of Python 3 super(). Help on class super in module builtins: class super(object) | super() -> same as super(__class__, <first argument>) | super(type) -> unbound super object | super(type, obj) -> bound super object; requires isinstance(obj, type) | super(type, type2) -> bound super object; requires issubclass(type2, type) Until now I've used super() only without arguments and it worked as expected (by a Java developer). Questions: What does "bound" mean in this context? What is the difference between bound and unbound super object? When to use super(type, obj) and when super(type, type2)? Would it be better to name the super class like in Mother.__init__(...)?

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  • Updating multiple Sprites - AS3 performance best practices

    - by dani
    Within the container "BubbleContainer" I have multiple "Bubble sprites". Each bubble's graphics object (a circle) is updated on a timer event. Let's say I have 50 Bubble sprites and each circle's radius should be updated with a mathematical formula. How do I organize this logic? How do I update all Bubble sprites within the BubbleContainer? (should I call a bubble.update() function or make a temporary reference to the graphics object?) Where do I put the Math logic? (as static functions?)

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  • Script stops while waiting for user input from STDIN.gets

    - by bob c
    I'm trying to do something like this, where I have two loops going in seperate threads. The problem I am having is that in the main thread, when I use gets and the script is waiting for user input, the other thread is stopped to wait as well. class Server def initialize() @server = TCPServer.new(8080) run end def run() @thread = Thread.new(@server) { |server| while true newsock = server.accept puts "some stuff after accept!" next if !newsock # some other stuff end } end end def processCommand() # some user commands here end test = Server.new while true do processCommand(STDIN.gets) end The above is just a sample of what I want to do. Is there a way to make the main thread block while waiting for user input?

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  • pass by reference or pass by value?

    - by Sven
    When learning a new programming language, one of the possible roadblocks you might encounter is the question whether the language is, by default, pass-by-value or pass-by-reference So here is my question to all of you, in your favorite language, how is it actually done? and what are the possible pitfalls? your favorite language can, of course, be anything you have ever played with: popular, obscure, esoteric, new, old ...

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  • Progress Bar design patterns?

    - by shoosh
    The application I'm writing performs a length algorithm which usually takes a few minutes to finish. During this time I'd like to show the user a progress bar which indicates how much of the algorithm is done as precisely as possible. The algorithm is divided into several steps, each with its own typical timing. For instance- initialization (500 milli-sec) reading inputs (5 sec) step 1 (30 sec) step 2 (3 minutes) writing outputs (7 sec) shutting down (10 milli-sec) Each step can report its progress quite easily by setting the range its working on, say [0 to 150] and then reporting the value it completed in its main loop. What I currently have set up is a scheme of nested progress monitors which form a sort of implicit tree of progress reporting. All progress monitors inherit from an interface IProgressMonitor: class IProgressMonitor { public: void setRange(int from, int to) = 0; void setValue(int v) = 0; }; The root of the tree is the ProgressMonitor which is connected to the actual GUI interface: class GUIBarProgressMonitor : public IProgressMonitor { GUIBarProgressMonitor(ProgressBarWidget *); }; Any other node in the tree are monitors which take control of a piece of the parent progress: class SubProgressMonitor : public IProgressMonitor { SubProgressMonitor(IProgressMonitor *parent, int parentFrom, int parentLength) ... }; A SubProgressMonitor takes control of the range [parentFrom, parentFrom+parentLength] of its parent. With this scheme I am able to statically divide the top level progress according to the expected relative portion of each step in the global timing. Each step can then be further subdivided into pieces etc' The main disadvantage of this is that the division is static and it gets painful to make changes according to variables which are discovered at run time. So the question: are there any known design patterns for progress monitoring which solve this issue?

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  • Is this the correct way of speaking to a "Content Manager" Class?

    - by DeanMc
    I am creating a silverlight site. I am currently breaking out my ideas into pieces of functionality. One of the idea's I have is the concept of a content manager. This is essentially a UI control with 4 regions. Top, Bottom, Right & Left. I also have a collection of objects that are considered "Menu Items". These are controls that function as a way to navigate around, similar to links. The idea I have is to implement an IMenuItem interface. Among the standard pieces of information (Text, PageReference, etc) I was also going to hold a reference to the content manager. My idea behind this thinking is that I can pass the PageReference to a property on the ContentManager and then call a method which knows how to update the content manager accordingly. Is this the best way of implementing this or is their some sort of pattern for it?

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  • Class Design - Returning a List<Object> From <Object>

    - by Mike
    Given a simple class: public class Person { public string FirstName; public string LastName; public string GetFullName() { return FirstName + LastName; } } The user of this class will populate a List<Person> object by reading an Xml file or some other data source. Should the logic for populating the List be in the Person class or should it just remain in the calling class? In other words, should there be a public List<Persons> GetPersons() method in the Person class or in the calling class? Or should the data accessor be in another class altogether? I know this is a rather simplistic question but I'm just curious how others typically do it.

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  • Strategy pattern and "action" classes explosion

    - by devoured elysium
    Is it bad policy to have lots of "work" classes(such as Strategy classes), that only do one thing? Let's assume I want to make a Monster class. Instead of just defining everything I want about the monster in one class, I will try to identify what are its main features, so I can define them in interfaces. That will allow to: Seal the class if I want. Later, other users can just create a new class and still have polymorphism by means of the interfaces I've defined. I don't have to worry how people (or myself) might want to change/add features to the base class in the future. All classes inherit from Object and they implement inheritance through interfaces, not from mother classes. Reuse the strategies I'm using with this monster for other members of my game world. Con: This model is rigid. Sometimes we would like to define something that is not easily achieved by just trying to put together this "building blocks". public class AlienMonster : IWalk, IRun, ISwim, IGrowl { IWalkStrategy _walkStrategy; IRunStrategy _runStrategy; ISwimStrategy _swimStrategy; IGrowlStrategy _growlStrategy; public Monster() { _walkStrategy = new FourFootWalkStrategy(); ...etc } public void Walk() { _walkStrategy.Walk(); } ...etc } My idea would be next to make a series of different Strategies that could be used by different monsters. On the other side, some of them could also be used for totally different purposes (i.e., I could have a tank that also "swims"). The only problem I see with this approach is that it could lead to a explosion of pure "method" classes, i.e., Strategy classes that have as only purpose make this or that other action. In the other hand, this kind of "modularity" would allow for high reuse of stratagies, sometimes even in totally different contexts. What is your opinion on this matter? Is this a valid reasoning? Is this over-engineering? Also, assuming we'd make the proper adjustments to the example I gave above, would it be better to define IWalk as: interface IWalk { void Walk(); } or interface IWalk { IWalkStrategy WalkStrategy { get; set; } //or something that ressembles this } being that doing this I wouldn't need to define the methods on Monster itself, I'd just have public getters for IWalkStrategy (this seems to go against the idea that you should encapsulate everything as much as you can!) Why? Thanks

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  • Using generics with XmlSerializer

    - by MainMa
    Hi, When using XML serialization in C#, I use code like this: public MyObject LoadData() { XmlSerializer xmlSerializer = new XmlSerializer(typeof(MyObject)); using (TextReader reader = new StreamReader(settingsFileName)) { return (MyObject)xmlSerializer.Deserialize(reader); } } (and similar code for deserialization). It requires casting and is not really nice. Is there a way, directly in .NET Framework, to use generics with serialization? That is to say to write something like: public MyObject LoadData() { // Generics here. XmlSerializer<MyObject> xmlSerializer = new XmlSerializer(); using (TextReader reader = new StreamReader(settingsFileName)) { // No casts nevermore. return xmlSerializer.Deserialize(reader); } }

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  • Why is Self assignable in Delphi?

    - by mjustin
    This code in a GUI application compiles and runs: procedure TForm1.Button1Click(Sender: TObject); begin Self := TForm1.Create(Owner); end; (tested with Delphi 6 and 2009) why is Self writeable and not read-only? in which situations could this be useful? Edit: is this also possible in Delphi Prism? (I think yes it is, see here) Update: Delphi applications/libraries which make use of Self assignment: python4delphi

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  • Concrete Types or Interfaces for return types?

    - by SDReyes
    Today I came to a fundamental paradox of the object programming style, concrete types or interfaces. Whats the better election for a method's return type: a concrete type or an interface? In most cases, I tend to use concrete types as the return type for methods. because I believe that an concrete type is more flexible for further use and exposes more functionality. The dark side of this: Coupling. The angelic one: A concrete type contains per-se the interface you would going to return initially, and extra functionality. What's your thumb's rule? Is there any programming principle for this? BONUS: This is an example of what I mean http://stackoverflow.com/questions/491375/readonlycollection-or-ienumerable-for-exposing-member-collections

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  • Avoiding RTTI In Java

    - by destructo_gold
    Hi, If I have a superclass, say Animal, and two subclasses: Zebra and Giraffe, If I decide to define a Vector of Animals: Vector <Animal> animals = new Vector(); and I want to say: You can add Giraffes, but you must own at least one Zebra first. What is the best way to do this without using RTTI? (instanceof)

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