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  • Looking for a better way to integrate a static list into a set of classes

    - by EvilTeach
    I'm trying to expand my sons interest from Warcraft 3 programming into C++ to broaden his horizons to a degree. We are planning on porting a little game that he wrote. The context goes something like this. There are Ships and Missiles, for which Ships will use Missiles and interact with them A Container exists which will hold 'a list' of ships. A Container exists which will hold 'a list' of planets. One can apply a function over all elements in the Container (for_each) Ships and Missles can be created/destroyed at any time New objects automatically insert themselves into the proper container. I cobbled a small example together to do that job, so we can talk about topics (list, templates etc) but I am not pleased with the results. #include <iostream> #include <list> using namespace std; /* Base class to hold static list in common with various object groups */ template<class T> class ObjectManager { public : ObjectManager ( void ) { cout << "Construct ObjectManager at " << this << endl; objectList.push_back(this); } virtual ~ObjectManager ( void ) { cout << "Destroy ObjectManager at " << this << endl; } void for_each ( void (*function)(T *) ) { for (objectListIter = objectList.begin(); objectListIter != objectList.end(); ++objectListIter) { (*function)((T *) *objectListIter); } } list<ObjectManager<T> *>::iterator objectListIter; static list<ObjectManager<T> *> objectList; }; /* initializer for static list */ template<class T> list<ObjectManager<T> *> ObjectManager<T>::objectList; /* A simple ship for testing */ class Ship : public ObjectManager<Ship> { public : Ship ( void ) : ObjectManager<Ship>() { cout << "Construct Ship at " << this << endl; } ~Ship ( void ) { cout << "Destroy Ship at " << this << endl; } friend ostream &operator<< ( ostream &out, const Ship &that ) { out << "I am a ship"; return out; } }; /* A simple missile for testing */ class Missile : public ObjectManager<Missile> { public : Missile ( void ) : ObjectManager<Missile>() { cout << "Construct Missile at " << this << endl; } ~Missile ( void ) { cout << "Destroy Missile at " << this << endl; } friend ostream &operator<< ( ostream &out, const Missile &that ) { out << "I am a missile"; return out; } }; /* A function suitable for the for_each function */ template <class T> void show ( T *it ) { cout << "Show: " << *it << " at " << it << endl; } int main ( void ) { /* Create dummy planets for testing */ Missile p1; Missile p2; /* Demonstrate Iterator */ p1.for_each(show); /* Create dummy ships for testing */ Ship s1; Ship s2; Ship s3; /* Demonstrate Iterator */ s1.for_each(show); return 0; } Specifically, The list is effectively embedded in each ship though the inheritance mechanism. One must have a ship, in order to access the list of ships. One must have a missile in order to be able to access the list of missiles. That feels awkward. My question boils down to "Is there a better way to do this?" Automatic object container creation Automatic object insertion Container access without requiring an object in the list to access it. I am looking for better ideas. All helpful entries get an upvote. Thanks Evil.

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  • Call a macro every time any method is called - Objective C

    - by Jacob Relkin
    Hi, I wrote a debug macro that prints to the console the passed-in string whenever the global kDebug flag == YES. I need to print out the name of a method and it's classname whenever any method is called. That works fine when i painstakingly go through every method and write the name of the class and the method in a string. Is there any special handler that gets called when any method in Objective-C is called, and if so, is there a way i can somehow override it to call my debug macro?? The entire purpose of this is so that I don't have to go through every method in my code and hand-code the method signature in the debug macro call. Thanks

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  • Why does the Java Collections Framework offer two different ways to sort?

    - by dvanaria
    If I have a list of elements I would like to sort, Java offers two ways to go about this. For example, lets say I have a list of Movie objects and I’d like to sort them by title. One way I could do this is by calling the one-argument version of the static java.util.Collections.sort( ) method with my movie list as the single argument. So I would call Collections.sort(myMovieList). In order for this to work, the Movie class would have to be declared to implement the java.lang.Comparable interface, and the required method compareTo( ) would have to be implemented inside this class. Another way to sort is by calling the two-argument version of the static java.util.Collections.sort( ) method with the movie list and a java.util.Comparator object as it’s arguments. I would call Collections.sort(myMovieList, titleComparator). In this case, the Movie class wouldn’t implement the Comparable interface. Instead, inside the main class that builds and maintains the movie list itself, I would create an inner class that implements the java.util.Comparator interface, and implement the one required method compare( ). Then I'd create an instance of this class and call the two-argument version of sort( ). The benefit of this second method is you can create an unlimited number of these inner class Comparators, so you can sort a list of objects in different ways. In the example above, you could have another Comparator to sort by the year a movie was made, for example. My question is, why bother to learn both ways to sort in Java, when the two-argument version of Collections.sort( ) does everything the first one-argument version does, but with the added benefit of being able to sort the list’s elements based on several different criteria? It would be one less thing to have to keep in your mind while coding. You’d have one basic mechanism of sorting lists in Java to know.

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  • JS: capture a static snapshot of an object at a point in time with a method

    - by Barney
    I have a JS object I use to store DOM info for easy reference in an elaborate GUI. It starts like this: var dom = { m:{ old:{}, page:{x:0,y:0}, view:{x:0,y:0}, update:function(){ this.old = this; this.page.x = $(window).width(); this.page.y = $(window).height(); this.view.x = $(document).width(); this.view.y = window.innerHeight || $(window).height(); } I call the function on window resize: $(window).resize(function(){dom.m.update()}); The problem is with dom.m.old. I would have thought that by calling it in the dom.m.update() method before the new values for the other properties are assigned, at any point in time dom.m.old would contain a snapshot of the dom.m object as of the last update – but instead, it's always identical to dom.m. I've just got a pointless recursion method. Why isn't this working? How can I get a static snapshot of the object that won't update without being specifically told to? Comments explaining how I shouldn't even want to be doing anything remotely like this in the first place are very welcome :)

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  • string extension method - Not available through WebMethod

    - by Peter Bridger
    I've written a simple extension method for a web project, it sits in a class file called StringExtensions.cs which contains the following code: using System; using System.Collections.Generic; using System.Linq; using System.Web; /// <summary> /// Useful extensions for string /// </summary> static class StringExtensions { /// <summary> /// Is string empty /// </summary> /// <param name="value"></param> /// <returns></returns> public static bool IsEmpty(this string value) { return value.Trim().Length == 0; } } I can access this extension method from all the classes I have within the App_Code directory. However I have a web page called JSON.aspx that contains a series of [WebMethods] - within these I cannot see the extension method - I must be missing something very obvious!

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  • C# reflection instantiation

    - by NickLarsen
    I am currently trying to create a generic instance factory for which takes an interface as the generic parameter (enforced in the constructor) and then lets you get instantiated objects which implement that interface from all types in all loaded assemblies. The current implementation is as follows:     public class InstantiationFactory     {         protected Type Type { get; set; }         public InstantiationFactory()         {             this.Type = typeof(T);             if (!this.Type.IsInterface)             {                 // is there a more descriptive exception to throw?                 throw new ArgumentException(/* Crafty message */);             }         }         public IEnumerable GetLoadedTypes()         {             // this line of code found in other stack overflow questions             var types = AppDomain.CurrentDomain.GetAssemblies()                 .SelectMany(a = a.GetTypes())                 .Where(/* lambda to identify instantiable types which implement this interface */);             return types;         }         public IEnumerable GetImplementations(IEnumerable types)         {             var implementations = types.Where(/* lambda to identify instantiable types which implement this interface */                 .Select(x = CreateInstance(x));             return implementations;         }         public IEnumerable GetLoadedImplementations()         {             var loadedTypes = GetLoadedTypes();             var implementations = GetImplementations(loadedTypes);             return implementations;         }         private T CreateInstance(Type type)         {             T instance = default(T);             var constructor = type.GetConstructor(Type.EmptyTypes);             if (/* valid to instantiate test */)             {                 object constructed = constructor.Invoke(null);                 instance = (T)constructed;             }             return instance;         }     } It seems useful to me to have my CreateInstance(Type) function implemented as an extension method so I can reuse it later and simplify the code of my factory, but I can't figure out how to return a strongly typed value from that extension method. I realize I could just return an object:     public static class TypeExtensions     {         public object CreateInstance(this Type type)         {             var constructor = type.GetConstructor(Type.EmptyTypes);             return /* valid to instantiate test */ ? constructor.Invoke(null) : null;         }     } Is it possible to have an extension method create a signature per instance of the type it extends? My perfect code would be this, which avoids having to cast the result of the call to CreateInstance():     Type type = typeof(MyParameterlessConstructorImplementingType);     MyParameterlessConstructorImplementingType usable = type.CreateInstance();

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  • Ruby module_function, invoking module's private method, invoked in class method style on module shows error

    - by Jignesh
    test_module.rb module MyModule def module_func_a puts "module_func_a invoked" private_b end module_function :module_func_a private def private_b puts "private_b invoked" end end class MyClass include MyModule def test_module module_func_a end end Invoking module function from class c = MyClass.new c.test_module Output 1: $ ruby test_module.rb module_func_a invoked private_b invoked Invoking module function on module in class method style ma = MyModule.module_func_a Output 2: module_func_a invoked test_module.rb:5:in `module_func_a': undefined local variable or method `private_b' for MyModule:Module (NameError) from test_module.rb:31 As can be seen from the Output 1 and Output 2 when including the module in a class, no issue occurs when a module's private method gets invoked from a module function while in case when directly invoking the module function on the module in class method style the module's private method, invoked from module function, is not found. Can anybody make me understand the reason behind above behavior and whether invoking module function (which in turn invokes module's private method) on module in class method style is possible or not? If possible, then what rectifications are required in my code to do the same? Thanks, Jignesh

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  • When is it better to use a method versus a property for a class definition?

    - by ccomet
    Partially related to an earlier question of mine, I have a system in which I have to store complex data as a string. Instead of parsing these strings as all kinds of separate objects, I just created one class that contains all of those objects, and it has some parser logic that will encode all properties into strings, or decode a string to get those objects. That's all fine and good. This question is not about the parser itself, but about where I should house the logic for the parser. Is it a better choice to put it as a property, or as a method? In the case of a property, say public string DataAsString, the get accessor would house the logic to encode all of the data into a string, while the set accessor would decode the input value and set all of the data in the class instance. It seems convenient because the input/output is indeed a string. In the case of a method, one method would be Encode(), which returns the encoded string. Then, either the constructor itself would house the logic for the decoding a string and require the string argument, or I write a Decode(string str) method which is called separately. In either case, it would be using a method instead of a property. So, is there a functional difference between these paths, in terms of the actual running of the code? Or are they basically equivalent and it then boils down to a choice of personal preference or which one looks better? And in that kind of question... which would look cleaner anyway?

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  • RenderAction in an HtmlHelperExtension Method?

    - by TimLeung
    I am trying to call the RenderAction Extension Method within my own Html Helper: System.Web.Mvc.Html.ChildActionExtensions.RenderAction(helper, "account", "login"); this is so that along with some additional logic, I would like all html helpers to use a common method name structure when calling it on the view: <%= Html.CompanyName().RenderAccount() %> but the problem I am having is that, asp.net will complain about not finding the actual route it needs to process. It does not take in the parameters of "controller" to be used as the action and "login" to be used as the action. It seems to only reference the current route. Any ideas how I can package up the RenderAction?

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  • Accessing non-static combbox property in the static method.

    - by Harikrishna
    I have one combobox on the window form and I have one method which is declared with static like private static DataTable ParseTable(HtmlNode table) Now I want to use combobox in that method for using combobox property but I can not access any property of combobox or combobox itself.If I made the combobox declaration as static then it can be accessed in that static method.But any alternative way to access combbox property in that static method because I don't want to make combobox declaration as static.

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  • Fast ArgumentNullException with attributes. It is possible?

    - by Fraga
    Hi. Is there any fast way to verify null arguments via attributes or something? Convert this: public void Method(type arg1,type arg2,type arg3) { if (arg1== null) throw new ArgumentNullException("arg1"); if (arg2== null) throw new ArgumentNullException("arg2"); if (arg3== null) throw new ArgumentNullException("arg3"); //Business Logic } Into something like this: [VerifyNullArgument("arg1","arg2","arg3")] public void Method(type arg1,type arg2,type arg3) { //Business Logic } Ideas? thanks guys.

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  • In an extension method how do a create an object based on the implementation class

    - by Greg
    Hi, In an extension method how do a create an object based on the implementation class. So in the code below I wanted to add an "AddRelationship" extension method, however I'm not sure how within the extension method I can create an Relationship object? i.e. don't want to tie the extension method to this particular implementation of relationship public static class TopologyExtns { public static void AddNode<T>(this ITopology<T> topIf, INode<T> node) { topIf.Nodes.Add(node.Key, node); } public static INode<T> FindNode<T>(this ITopology<T> topIf, T searchKey) { return topIf.Nodes[searchKey]; } public static bool AddRelationship<T>(this ITopology<T> topIf, INode<T> parentNode, INode<T> childNode) { var rel = new RelationshipImp(); // ** How do I create an object from teh implementation // Add nodes to Relationship // Add relationships to Nodes } } public interface ITopology<T> { //List<INode> Nodes { get; set; } Dictionary<T, INode<T> > Nodes { get; set; } } public interface INode<T> { // Properties List<IRelationship<T>> Relationships { get; set; } T Key { get; } } public interface IRelationship<T> { // Parameters INode<T> Parent { get; set; } INode<T> Child { get; set; } } namespace TopologyLibrary_Client { class RelationshipsImp : IRelationship<string> { public INode<string> Parent { get; set; } public INode<string> Child { get; set; } } } public class TopologyImp<T> : ITopology<T> { public Dictionary<T, INode<T>> Nodes { get; set; } public TopologyImp() { Nodes = new Dictionary<T, INode<T>>(); } } thanks

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  • Rails NoMethodError in loop when method exists

    - by Kevin Whitaker
    Good day all. I'm running into a bit of a problem getting a script running on my production environment, even though it works just fine on my dev box. I've verified that all the requisite gems and such are the same version. I should mention that the script is intended to be run with the script/runner command. Here is a super-condensed version of what I'm trying to do, centered around the part that's broken: def currentDeal marketTime = self.convertToTimeZone(Time.new) deal = Deal.find(:first, :conditions = ["start_time ? AND market_id = ? AND published = ?", marketTime, marketTime, self.id, 1]) return deal end markets = Market.find(all) markets.each do |market| deal = market.currentDeal puts deal.subject end Now convertToTimeZone is a method attached to the model. So, this code works just fine on my dev machine, as stated. However, attempting to run it on my production machine results in: undefined method `subject' for nil:NilClass (NoMethodError) If, however, I go into the console on the production box and do this: def currentDeal marketTime = self.convertToTimeZone(Time.new) deal = Deal.find(:first, :conditions = ["start_time ? AND market_id = ? AND published = ?", marketTime, marketTime, self.id, 1]) return deal end market = Market.find(1) deal = market.currentDeal puts deal.subject It returns the correct value, no problem. So what is going on? This is on rails v 2.3.5, on both machines. Thanks for any help

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  • Lisp, OCaml or what for Runge Kutta?

    - by Eelvex
    Which language would you propose for solving a system with: first order differential equations complex variables N-dimensions using 4th order Runge Kutta or the like. Speed matters a lot but would sacrifice for: Elegant (clean and short) code Flexibility + scalability I'm mostly between a Lisp and OCaml but any other suggestion is welcomed. Thanks!

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  • Does Java support default parameter values?

    - by gnavi
    I came across some Java code that had the following structure: public MyParameterizedFunction(String param1, int param2) { this(param1, param2, false); } public MyParameterizedFunction(String param1, int param2, boolean param3) { //use all three parameters here } I know that in C++ I can assign a parameter a default value. For example: void MyParameterizedFunction(String param1, int param2, bool param3=false); Does Java support this kind of syntax? Are there any reasons why this two step syntax is preferable?

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  • Runge-Kutta Method with adaptive step

    - by infoholic_anonymous
    I am implementing Runge-Kutta method with adaptive step in matlab. I get different results as compared to matlab's own ode45 and my own implementation of Runge-Kutta method with fixed step. What am I doing wrong in my code? Is it possible? function [ result ] = rk4_modh( f, int, init, h, h_min ) % % f - function handle % int - interval - pair (x_min, x_max) % init - initial conditions - pair (y1(0),y2(0)) % h_min - lower limit for h (step length) % h - initial step length % x - independent variable ( for example time ) % y - dependent variable - vertical vector - in our case ( y1, y2 ) function [ k1, k2, k3, k4, ka, y ] = iteration( f, h, x, y ) % core functionality performed within loop k1 = h * f(x,y); k2 = h * f(x+h/2, y+k1/2); k3 = h * f(x+h/2, y+k2/2); k4 = h * f(x+h, y+k3); ka = (k1 + 2*k2 + 2*k3 + k4)/6; y = y + ka; end % constants % relative error eW = 1e-10; % absolute error eB = 1e-10; s = 0.9; b = 5; % initialization i = 1; x = int(1); y = init; while true hy = y; hx = x; %algorithm [ k1, k2, k3, k4, ka, y ] = iteration( f, h, x, y ); % error estimation for j=1:2 [ hk1, hk2, hk3, hk4, hka, hy ] = iteration( f, h/2, hx, hy ); hx = hx + h/2; end err(:,i) = abs(hy - y); % step adjustment e = abs( hy ) * eW + eB; a = min( e ./ err(:,i) )^(0.2); mul = a * s; if mul >= 1 % step length admitted keepH(i) = h; k(:,:,i) = [ k1, k2, k3, k4, ka ]; previous(i,:) = [ x+h, y' ]; %' i = i + 1; if floor( x + h + eB ) == int(2) break; else h = min( [mul*h, b*h, int(2)-x] ); x = x + keepH(i-1); end else % step length requires further adjustments h = mul * h; if ( h < h_min ) error('Computation with given precision impossible'); end end end result = struct( 'val', previous, 'k', k, 'err', err, 'h', keepH ); end The function in question is: function [ res ] = fun( x, y ) % res(1) = y(2) + y(1) * ( 0.9 - y(1)^2 - y(2)^2 ); res(2) = -y(1) + y(2) * ( 0.9 - y(1)^2 - y(2)^2 ); res = res'; %' end The call is: res = rk4( @fun, [0,20], [0.001; 0.001], 0.008 ); The resulting plot for x1 : The result of ode45( @fun, [0, 20], [0.001, 0.001] ) is:

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  • Returning IEnumerable<T> vs IQueryable<T>

    - by stackoverflowuser
    what is the difference between returning iqueryable vs ienumerable. IQueryable<Customer> custs = from c in db.Customers where c.City == "<City>" select c; IEnumerable<Customer> custs = from c in db.Customers where c.City == "<City>" select c; Will both be deferred execution? When should one be preferred over the other?

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  • Kohana Database Library - How to Execute a Query with the Same Parameters More Than Once?

    - by Noah Goodrich
    With the following bit of code: $builder = ORM::factory('branch')->where('institution_id', $this->institution->id)->orderby('name'); I need to first execute: $count = $builder->count_all(); Then I need to execute: $rs = $builder->find_all($limit, $offset); However, it appears that when I execute the first query the stored query parameters are cleared so that a fresh query can be executed. Is there a way to avoid having the parameters cleared or at least copy them easily without having to reach directly into the Database driver object that stores the query parameters and copy them out? We are using Kohana 2.3.4 and upgrading is not an option.

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  • Visual Studio Formatting -- Change Method Color

    - by Daniel
    The default appearance of a method for example, ".ToString()" is by default the color black. I want to make it a different color to stand out but I do not see any options that reference this option specifically. I remember one of former collegues showing me his VS IDE years ago and he had it setup this way but I cannot recall what he did. Does anyone have any ideas on how to do this?

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  • Fatal error: Function name must be a string in.. PHP error

    - by Jonesy
    Hi I have a class called User and a method called insertUser(). function insertUser($first_name, $last_name, $user_name, $password, $email_address, $group_house_id) { $first_name = mysql_real_escape_string($first_name); $last_name = mysql_real_escape_string($last_name); $user_name = mysql_real_escape_string($user_name); $password = mysql_real_escape_string($password); $email_address = mysql_real_escape_string($email_address); $query = "INSERT INTO Users (FirstName,LastName,UserName,Password,EmailAddress, GroupHouseID) VALUES ('$first_name','$last_name','$user_name','$password','$email_address','$group_house_id')"; $mysql_query($query); } And I call it like this: $newUser = new User(); $newUser->insertUser($first_name, $last_name, $user_name, $email, $password, $group_house_id); When I run the code I get this error: Fatal error: Function name must be a string in /Library/WebServer/Documents/ORIOnline/includes/class_lib.php on line 33 Anyone know what I am doing wronly? Also, this is my first attempt at OO PHP. Cheers, Jonesy

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  • private class calling a method from its outer class

    - by oxinabox.ucc.asn.au
    Ok, so I have a class for a "Advanced Data Structure" (in this case a kinda tree) SO I implimented a Iterator as a private class with in it. So the iterator needs to implement a remove function to remove the last retuirned element. now my ADT already impliments a remove function, and in this case there is very little (thinking about it, i think nothing) to be gain by implimenting a different remove function for the iterator. so how do I go about calling the remove from my ADT sketch of my struture: public class ADT { ... private class ADT_Iterator impliments java.util.Itorator{ ... public void remove(){ //where I want to call the ADT's remove function from } ... public void remove( Object paramFoo ) { ... } ... } So just calling remove(FooInstance) won't work (will it?) and this.remove(FooInstance) is the same thing. what do i call? (and changign the name of the ADT's remove function is not an option, as that AD T has to meet an Interace wich I am note at liberty to change) I could make both of them call a removeHelper functon, I guess...

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  • What's an easy way to set up object communication in Obj-C?

    - by seaworthy
    I am trying to send a slider value from a controller object to a method of a model object. The later is implemented in the separate file and I have appropriate headers. I think the problem is that I am not sure how to instantiate the receiver in order to produce a working method for the controller. Here is the controller's method. -(IBAction)setValue:(id)slider {[Model setValue:[slider floatValue]];} @implementation Model -(void)setValue:(float)n{ printf("%f",n); } @end What I get is 'Model' may not respond to '+setValue' warning and no output in my console. Any insight is appreciated.

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  • C# extension method doesn't seem to exist

    - by blahblah
    I can't seem to get the following extension method to be found in another class in the same namespace (MyProject.Util). using System.Collections.Specialized; namespace MyProject.Util { public static class Extensions { public static string Get( this NameValueCollection me, string key, string def ) { return me[key] ?? def; } } } As you can see it's basically another version of foo[bar] ?? baz, but I still don't understand why VS2008 fails to compile telling me that no version of Get takes two arguments. Any ideas?

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  • Getting the name of a child class in the parent class (static context)

    - by Benoit Myard
    Hi everybody, I'm building an ORM library with reuse and simplicity in mind; everything goes fine except that I got stuck by a stupid inheritance limitation. Please consider the code below: class BaseModel { /* * Return an instance of a Model from the database. */ static public function get (/* varargs */) { // 1. Notice we want an instance of User $class = get_class(parent); // value: bool(false) $class = get_class(self); // value: bool(false) $class = get_class(); // value: string(9) "BaseModel" $class = __CLASS__; // value: string(9) "BaseModel" // 2. Query the database with id $row = get_row_from_db_as_array(func_get_args()); // 3. Return the filled instance $obj = new $class(); $obj->data = $row; return $obj; } } class User extends BaseModel { protected $table = 'users'; protected $fields = array('id', 'name'); protected $primary_keys = array('id'); } class Section extends BaseModel { // [...] } $my_user = User::get(3); $my_user->name = 'Jean'; $other_user = User::get(24); $other_user->name = 'Paul'; $my_user->save(); $other_user->save(); $my_section = Section::get('apropos'); $my_section->delete(); Obviously, this is not the behavior I was expecting (although the actual behavior also makes sense).. So my question is if you guys know of a mean to get, in the parent class, the name of child class.

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