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  • List<> of objects, different types, sort and pull out types individually?

    - by Brazos
    I've got a handful of products, any, all, or none of which may be associated with a specific submission. All 7 products are subclasses of the class Product. I need to store all the products associated with a submission, and then retrieve them and their field data on my presentation layer. I've been using a List, and List, but when I use the OfType, I throw an error saying that I can't implicitly convert systems.generic.IEnumerable to type 'Product'. I've tried to cast, but to no avail. When I use prodlist.OfType<EPL>(); there are no errors, but when I try and store that in an instance of EPL "tempEpl", I get the aforementioned cast-related error. What gives? Code below. ProductService pserv = new ProductService(); IList<object> prodlist = pserv.getProductById(x); EPL tempEpl = new EPL(); if ((prodlist.OfType<EPL>()) != null) { tempEpl = prodlist.OfType<EPL>(); // this throws a conversion error. } the Data layer List<object> TempProdList = new List<object>(); conn.Open(); SqlCommand EplCmd = new SqlCommand(EPLQuery, conn); SqlDataReader EplRead = null; EplRead = EplCmd.ExecuteReader(); EPL TempEpl = new EPL(); if (EplRead.Read()) { TempEpl.Entity1 = EplRead.GetString(0); TempEpl.Employees1 = EplRead.GetInt32(1); TempEpl.CA1 = EplRead.GetInt32(2); TempEpl.MI1 = EplRead.GetInt32(3); TempEpl.NY1 = EplRead.GetInt32(4); TempEpl.NJ1 = EplRead.GetInt32(5); TempEpl.PrimEx1 = EplRead.GetInt32(6); TempEpl.EplLim1 = EplRead.GetInt32(7); TempEpl.EplSir1 = EplRead.GetInt32(8); TempEpl.Premium1 = EplRead.GetInt32(9); TempEpl.Wage1 = EplRead.GetInt32(10); TempEpl.Sublim1 = EplRead.GetInt32(11); TempProdList.Add(TempEpl); }

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  • systematizing error codes for a web app in php?

    - by user151841
    I'm working on a class-based php web app. I have some places where objects are interacting, and I have certain situations where I'm using error codes to communicate to the end user -- typically when form values are missing or invalid. These are situations where exceptions are unwarranted ( and I'm not sure I could avoid the situations with exceptions anyways). In one object, I have some 20 code numbers, each of which correspond to a user-facing message, and a admin/developer-facing message, so both parties know what's going on. Now that I've worked over the code several times, I find that it's difficult to quickly figure out what code numbers in the series I've already used, so I accidentally create conflicting code numbers. For instance, I just did that today with 12, 13, 14 and 15. How can I better organize this so I don't create conflicting error codes? Should I create one singleton class, errorCodes, that has a master list of all error codes for all classes, systematizing them across the whole web app? Or should each object have its own set of error codes, when appropriate, and I just keep a list in the commentary of the object, to use and update that as I go along?

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  • Explicit method tables in C# instead of OO - good? bad?

    - by FunctorSalad
    Hi! I hope the title doesn't sound too subjective; I absolutely do not mean to start a debate on OO in general. I'd merely like to discuss the basic pros and cons for different ways of solving the following sort of problem. Let's take this minimal example: you want to express an abstract datatype T with functions that may take T as input, output, or both: f1 : Takes a T, returns an int f2 : Takes a string, returns a T f3 : Takes a T and a double, returns another T I'd like to avoid downcasting and any other dynamic typing. I'd also like to avoid mutation whenever possible. 1: Abstract-class-based attempt abstract class T { abstract int f1(); // We can't have abstract constructors, so the best we can do, as I see it, is: abstract void f2(string s); // The convention would be that you'd replace calls to the original f2 by invocation of the nullary constructor of the implementing type, followed by invocation of f2. f2 would need to have side-effects to be of any use. // f3 is a problem too: abstract T f3(double d); // This doesn't express that the return value is of the *same* type as the object whose method is invoked; it just expresses that the return value is *some* T. } 2: Parametric polymorphism and an auxilliary class (all implementing classes of TImpl will be singleton classes): abstract class TImpl<T> { abstract int f1(T t); abstract T f2(string s); abstract T f3(T t, double d); } We no longer express that some concrete type actually implements our original spec -- an implementation is simply a type Foo for which we happen to have an instance of TImpl. This doesn't seem to be a problem: If you want a function that works on arbitrary implementations, you just do something like: // Say we want to return a Bar given an arbitrary implementation of our abstract type Bar bar<T>(TImpl<T> ti, T t); At this point, one might as well skip inheritance and singletons altogether and use a 3 First-class function table class /* or struct, even */ TDictT<T> { readonly Func<T,int> f1; readonly Func<string,T> f2; readonly Func<T,double,T> f3; TDict( ... ) { this.f1 = f1; this.f2 = f2; this.f3 = f3; } } Bar bar<T>(TDict<T> td; T t); Though I don't see much practical difference between #2 and #3. Example Implementation class MyT { /* raw data structure goes here; this class needn't have any methods */ } // It doesn't matter where we put the following; could be a static method of MyT, or some static class collecting dictionaries static readonly TDict<MyT> MyTDict = new TDict<MyT>( (t) => /* body of f1 goes here */ , // f2 (s) => /* body of f2 goes here */, // f3 (t,d) => /* body of f3 goes here */ ); Thoughts? #3 is unidiomatic, but it seems rather safe and clean. One question is whether there are any performance concerns with it. I don't usually need dynamic dispatch, and I'd prefer if these function bodies get statically inlined in places where the concrete implementing type is known statically. Is #2 better in that regard?

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  • HMVC or PAC - how to handle shared abstractions/models?

    - by fig-gnuton
    In HMVC/PAC, what's the recommended way to code if two or more triads/agents share a common model/abstraction? Do you instantiate a new instance of that model wherever needed, and propogate a change in one to all the other instances via the controllers? Or do instantiate one model at some common upper level, and inject that instance wherever needed? (Or neither if I'm missing something fundamental about these patterns?)

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  • PHP MVC: How to implement an effective Controller/View Association like ZendFramework guys do!

    - by Navi
    Hi, I am making my own PHP-MVC framework. i have a question regarding Controller and View Association. I love the way Zend framework uses view within Controller as follow: $this->view->data = 'Data here'; so it can be used in view as follow: echo $this->data; I am wondering how can i implement this association. I want to remove codes between /** **/ and want to replace with some magic functions. My codes for controller as as follow: class UserController extends Controller{ /************************************/ public function __construct(){ $this->view = new View(); $this->view->setLayout( 'home' ); } function __destruct(){ $this->view->render(); } /************************************/ public function index(){ $this->redirect('user/login'); } public function login(){ } public function register(){ } public function forgotPassword(){ } } Thanks and best regards, -Navi

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  • What are the advantages of learning Go?

    - by Pangea
    What is so unique about Go? Over the 11 years of my career I've learnt Pascal, C, C++, COBOL and then Java. I always felt that going from C to C++ to Java was a incremental and value added progression. Now I see a proliferation of functional programming languages and I understand the benefit of learning few of them (like actors in scala etc). Now I was going through the Go programming language and was wondering why would I want to learn this? Is this going to simplify how I have been writing the code? What are its use cases? How can I make a case to promote it in my team? What is the next programming language that a Java team that builds business applications like us can benefit from? Appreciate your comments on this.

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  • PHP object class variable

    - by mck89
    I have built a class in PHP and I must declare a class variable as an object. Everytime I want to declare an empty object I use: $var=new stdClass; But if I use it to declare a class variable as class foo { var $bar=new stdClass; } a parse error occurs. Is there a way to do this or must I declare the class variable as an object in the constructor function? PS: I'm using PHP 4.

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  • what's Static type safety ?

    - by symfony
    Static type safety – an integral property of languages of the family to which C++ belongs and valuable both for guaranteeing properties of a design and for providing runtime and space efficiency. Can someone illustrate by a demo? Thanks

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  • Singletons and other design issues

    - by Ahmed Saleh
    I have worked using different languages like C++/Java and currently AS3. Most applications were computer vision, and small 2D computer games. Most companies that I have worked for, they use Singletons in a language like AS3, to retrieve elements or classes in an easy way. Their problem is basically they needs some variables or to call other functions from other classes. In a language like AS3, there is no private constructor, and they write a hacky code to prevent new instances. In Java and C++ I also faced the situation that I need to use other classe's members or to call their functions in different classes. The question is, is there a better or another design, to let other classes interact with each others without using singletons? I feel that composition is the answer, but I need more detailed solutions or design suggestions.

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  • How do I create a class repository in Java and do I really need it?

    - by Roman
    I have a large number of objects which are identified by names (strings). So, I would like to have a kind of mapping from object name to the class instances. I was told that in this situation I can use a "repository" class which works like that: Server myServer = ServerRepository.getServer("NameOfServer"); So, if there is already an object (sever) with the "NameOfServer" it will be returned by the "getServer". If such an object does not exist yet, it will be created and returned by the "getServer". So, my question is how to program such a "repository" class? In this class I have to be able to check if there is an instance of a given class such that it has a given value of a given field. How can I do it? I need to have a kind of loop over all existing object of a given class? Another part of my question is why I cannot use associative arrays (associative container, map, mapping, dictionary, finite map)? (I am not sure how do you call it in Java) In more details, I have an "array" which maps names of objects to objects. So, whenever I create a new object, I add a new element to the array: myArray["NameOfServer"] = new Server("NameOfServer").

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  • C++ overloading virtual = operator

    - by taz
    Hello, here is the code for my question: class ICommon { public: virtual ICommon& operator=(const ICommon & p)const=0; }; class CSpecial : public ICommon { public: CSpecial& operator=(const CSpecial & cs) { //custom operations return *this; } }; CSpecial obj; Basically: I want the interface ICommon to force it's descendants to implement = operator but don't want to have any typecasts in the implementation. The compiler says "can't instantiate an abstract class. Any help/advice will be appreciated.

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  • How to restrict an access to some of the functions at third level in Classes (OOPs)

    - by Shantanu Gupta
    I have created a class say A which has some functions defined as protected. Now Class B inherits A and class C inherits B. Class A has private default constructor and protected parameterized constructor. I want Class B to be able to access all the protected functions defined in Class A but class C can have access on some of the functions only not all the functions and class C is inheriting class B. How can I restrict access to some of the functions of Class A from Class C ? Class A { private A(){} protected A(int ){} } Class B : A {} CLass C:B { }

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  • Is there any short way to load data to the properties of a class, for each column name matching the properties of the class?

    - by Ugur Gümüshan
    I want to load data to an instance of an object using its constructor and I write $this->property=$row["colname"] each time for each property. the mysql_fetch_object function fetches the data as an object but I am not sure if the instance of an object can be assigned to some object from inside. othwerwise I would use __construct($object) { $this=$object; } //doesn't give any syntax error Maybe I should look into iteration of properties and use foreach($object as $key => $value) $value=$object[$key]; or can I assign like $this=$object; within the constructor?

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  • Static vs Non Static 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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  • how to return the current object?

    - by ajsie
    in code igniter you can type: $query = $this->db->query("YOUR QUERY"); foreach ($query->result() as $row) { echo $row->title; echo $row->name; echo $row->body; } i guess that the query method returns the object it's part of. am i correct? if i am, how do you type the line where it returns the object? so what i wonder is how it looks like inside the query method for the above code to be functional. public function query($sql) { // some db logic here with the $sql and saves the values to the properties (title, name and body) return X } with other words, what should X be?

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  • What's the idiomatic way of inheriting data access functionality as well as object properties?

    - by Knut Arne Vedaa
    Suppose the following (slightly pseudo-code for brevity): class Basic { String foo; } class SomeExtension extends Basic { String bar; } class OtherExtension extends Basic { String baz; } class BasicService { Basic getBasic() { } } class SomeExtensionService extends BasicService { SomeExtension getSomeExtension() { } } class OtherExtensionService extends BasicService { OtherExtension getOtherExtension() { } } What would be the most idiomatic, elegant way to implement the get-() service methods with the most possible code reuse? Obviously you could do it like this: class BasicService { Basic getBasic() { Basic basic = new Basic(); basic.setFoo("some kind of foo"); return basic; } } class SomeExtensionService { SomeExtension getSomeExtension() { SomeExtension someExtension = new SomeExtension; Basic basic = getBasic(); someExtension.setFoo(basic.getFoo()); someExtension.setBar("some kind of bar"); return someExtension; } } But this would be ugly if Basic has a lot of properties, and also you only need one object, as SomeExtension already inherits Basic. However, BasicService can obviously not return a SomeExtension object. You could also have the get methods not create the object themselves, but create it at the outermost level and pass it to the method for filling in the properties, but I find that too imperative. (Please let me know if the question is confusingly formulated.)

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  • when does static member gets memory.

    - by vaibhav
    I have a class which have a static member. As I understand all static members are common for all instance of the class. So it means static members would get memory only once. Where is this memory is allocated (Stack or Heap) and when this memory get allocated.

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  • How to maintain a pool of names ?

    - by Jacques René Mesrine
    I need to maintain a list of userids (proxy accounts) which will be dished out to multithreaded clients. Basically the clients will use the userids to perform actions; but for this question, it is not important what these actions are. When a client gets hold of a userid, it is not available to other clients until the action is completed. I'm trying to think of a concurrent data structure to maintain this pool of userids. Any ideas ? Would a ConcurrentQueue do the job ? Clients will dequeue a userid, and add back the userid when they are finished with it.

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  • How to set default values to all wrong or null parameters of method?

    - by Roman
    At the moment I have this code (and I don't like it): private RenderedImage private RenderedImage getChartImage (GanttChartModel model, String title, Integer width, Integer height, String xAxisLabel, String yAxisLabel, Boolean showLegend) { if (title == null) { title = ""; } if (xAxisLabel == null) { xAxisLabel = ""; } if (yAxisLabel == null) { yAxisLabel = ""; } if (showLegend == null) { showLegend = true; } if (width == null) { width = DEFAULT_WIDTH; } if (height == null) { height = DEFAULT_HEIGHT; } ... } How can I improve it? I have some thoughts about introducing an object which will contain all these parameters as fields and then, maybe, it'll be possible to apply builder pattern. But still don't have clear vision how to implement that and I'm not sure that it's worth to be done. Any other ideas?

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  • Limiting method access in protected section to few classes

    - by Bharat
    Hi, I want to limit the access of protected methods to certain inherited classes only. For example there is a base class like TBase = Class Protected Method1; Method2; Method3; Method4; End; I have two classes derived from TBase TDerived1 = Class(TBase) //Here i must access only Method1 and Method2 End; TDerived2 = Class(TBase) //Here i must access only Method3 and Method4 End; Then is it possible to access only Method1 and Method2 when i use objects of TDerived1 and Method3 and Method4 when i use objects of TDerived2

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