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  • Generics in return types of static methods and inheritance

    - by Axel
    Generics in return types of static methods do not seem to get along well with inheritance. Please take a look at the following code: class ClassInfo<C> { public ClassInfo(Class<C> clazz) { this(clazz,null); } public ClassInfo(Class<C> clazz, ClassInfo<? super C> superClassInfo) { } } class A { public static ClassInfo<A> getClassInfo() { return new ClassInfo<A>(A.class); } } class B extends A { // Error: The return type is incompatible with A.getClassInfo() public static ClassInfo<B> getClassInfo() { return new ClassInfo<B>(B.class, A.getClassInfo()); } } I tried to circumvent this by changing the return type for A.getClassInfo(), and now the error pops up at another location: class ClassInfo<C> { public ClassInfo(Class<C> clazz) { this(clazz,null); } public ClassInfo(Class<C> clazz, ClassInfo<? super C> superClassInfo) { } } class A { public static ClassInfo<? extends A> getClassInfo() { return new ClassInfo<A>(A.class); } } class B extends A { public static ClassInfo<? extends B> getClassInfo() { // Error: The constructor ClassInfo<B>(Class<B>, ClassInfo<capture#1-of ? extends A>) is undefined return new ClassInfo<B>(B.class, A.getClassInfo()); } } What is the reason for this strict checking on static methods? And how can I get along? Changing the method name seems awkward.

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  • c++ templates and inheritance

    - by Armen Ablak
    Hey, I'm experiencing some problems with breaking my code to reusable parts using templates and inheritance. I'd like to achieve that my tree class and avltree class use the same node class and that avltree class inherits some methods from the tree class and adds some specific ones. So I came up with the code below. Compiler throws an error in tree.h as marked below and I don't really know how to overcome this. Any help appreciated! :) node.h: #ifndef NODE_H #define NODE_H #include "tree.h" template <class T> class node { T data; ... node() ... friend class tree<T>; }; #endif tree.h #ifndef DREVO_H #define DREVO_H #include "node.h" template <class T> class tree { public: //signatures tree(); ... void insert(const T&); private: node<T> *root; //missing type specifier - int assumed. Note: C++ does not support default-int }; //implementations #endif avl.h #ifndef AVL_H #define AVL_H #include "tree.h" #include "node.h" template <class T> class avl: public tree<T> { public: //specific int findMin() const; ... protected: void rotateLeft(node<T> *)const; private: node<T> *root; }; #endif avl.cpp (I tried separating headers from implementation, it worked before I started to combine avl code with tree code) #include "drevo" #include "avl.h" #include "vozlisce.h" template class avl<int>; //I know that only avl with int can be used like this, but currently this is doesn't matter :) //implementations ...

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  • Inheritance concept java..help

    - by max
    Hi everyone. I'd be very grateful if someone could help me to understand the inheritance concept in Java. Is the following code an example of that? I mean the class WavPanel is actually a subclass of JPanel which acts as a superclass. Is that correct? If so it means that "what JPanel has, also WavPanel but it is more specific since through its methods you can do something else". Am I wrong? thank you. Max import javax.swing.JPanel; class WavPanel extends JPanel { List<Byte> audioBytes; List<Line2D.Double> lines; public WavPanel() { super(); setBackground(Color.black); resetWaveform(); } public void resetWaveform() { audioBytes = new ArrayList<Byte>(); lines = new ArrayList<Line2D.Double>(); repaint(); } }

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  • Inheritance not working

    - by Pendo826
    Hey im just practicing inheritance and i encountered a problem. Im getting an error in my car class(sub-class) that the variables in Vehicle(parent) are not visible. i didnt do anything to change this and i dont even know how to make it invisible. Can anyone help me with this. public class Vehicle { private String make, model, colour; private int registrationNumber; public Vehicle() { this.make = ""; this.model = ""; this.colour = ""; this.registrationNumber = 0; } public Vehicle(String make, String model, String colour, int registrationNumber) { this.make = make; this.model = model; this.colour = colour; this.registrationNumber = registrationNumber; } public String getMake() { return make; } public void setMake(String make) { this.make = make; } public String getModel() { return model; } public void setModel(String model) { this.model = model; } public String getColour() { return colour; } public void setColour(String colour) { this.colour = colour; } public int getRegistrationNumber() { return registrationNumber; } public void setRegistrationNumber(int registrationNumber) { this.registrationNumber = registrationNumber; } public String toString() { return "Vehicle [make=" + make + ", model=" + model + ", colour=" + colour + ", registrationNumber=" + registrationNumber + "]"; } } public Car() { super(); this.doors = 0; this.shape = ""; } public Car(int doors, String shape, String make, String model, String colour, int registrationNumber) { super(); this.doors = doors; this.shape = shape; this.make = make;//Error this.model = model;//Error this.colour = colour;//Error this.registrationNumber = registrationNumber;//Error } The error message: Description Resource Path Location Type The field Vehicle.make is not visible Car.java /VehicleApp/src line 19 Java Problem The field Vehicle.model is not visible Car.java /VehicleApp/src line 20 Java Problem The field Vehicle.colour is not visible Car.java /VehicleApp/src line 21 Java Problem The field Vehicle.registrationNumber is not visible Car.java /VehicleApp/src line 22 Java Problem

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  • Resolving ambiguous this pointer in C++

    - by Paul Tevis
    I'm trying to derive a new class from an old one. The base class declaration looks like this: class Driver : public Plugin, public CmdObject { protected: Driver(); public: static Driver* GetInstance(); virtual Engine& GetEngine(); public: // Plugin methods... virtual bool InitPlugin (Mgr* pMgr); virtual bool Open(); virtual bool Close(); // CmdObject virtual bool ExecObjCmd(uint16 cmdID, uint16 nbParams, CommandParam *pParams, CmdChannelError& error); Mgr *m_pMgr; protected: Services *m_pServices; Engine m_Engine; }; Its constructor looks like this: Driver::Driver() : YCmdObject("Driver", (CmdObjectType)100, true), m_Engine("MyEngine") { Services *m_pServices = NULL; Mgr *m_pMgr = NULL; } So when I created my derived class, I first tried to simply inherit from the base class: class NewDriver : public Driver and copy the constructor: NewDriver::NewDriver() : CmdObject("NewDriver", (EYCmdObjectType)100, true), m_Engine("MyNewEngine") { Services *m_pServices = NULL; Mgr *m_pMgr = NULL; } The compiler (VisualDSP++ 5.0 from Analog Devices) didn't like this: ".\NewDriver.cpp", line 10: cc0293: error: indirect nonvirtual base class is not allowed CmdObject("NewDriver", (EYCmdObjectType)100, true), That made sense, so I decided to directly inherit from Plugin and CmdObject. To avoid multiple inheritance ambiguity problems (so I thought), I used virtual inheritance: class NewDriver : public Driver, public virtual Plugin, public virtual CmdObject But then, in the implementation of a virtual method in NewDriver, I tried to call the Mgr::RegisterPlugin method that takes a Plugin*, and I got this: ".\NewDriver.cpp", line 89: cc0286: error: base class "Plugin" is ambiguous if (!m_pMgr->RegisterPlugin(this)) How is the this pointer ambiguous, and how do I resolve it? Thanks, --Paul

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  • Django conditional template inheritance

    - by Ed
    I have template that displays object elements with hyperlinks to other parts of my site. I have another function that displays past versions of the same object. In this display, I don't want the hyperlinks. I'm under the assumption that I can't dynamically switch off the hyperlinks, so I've included both versions in the same template. I use an if statement to either display the hyperlinked version or the plain text version. I prefer to keep them in the same template because if I need to change the format of one, it will be easy to apply it to the other right there. The template extends framework.html. Framework has a breadcrumb system and it extends base.html. Base has a simple top menu system. So here's my dilemma. When viewing the standard hyperlink data, I want to see the top menu and the breadcrumbs. But when viewing the past version plain text data, I only want the data, no menu, no breadcrumbs. I'm unsure if this is possible given my current design. I tried having framework inherit the primary template so that I could choose to call either framework (and display the breadcrumbs), or the template itself, thus skipping the breadcrumbs, but I want framework.html available for other templates as well. If framework.html extends a specific template, I lose the ability to display it in other templates. I tried writing an if statement that would display a the top_menu block and the nav_menu block from base.html and framework.html respectively. This would overwrite their blocks and allow me to turn off those elements conditional on the if. Unfortunately, it doesn't appear to be conditional; if the block elements are in the template at all, surrounded by an if or not, I lose the menus. I thought about using {% include %} to pick up the breadcrumbs and a split out top menu. In that case though, I'll have to include it all the time. No more inheritance. Is this the best option given my requirement?

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  • Can simple javascript inheritance be simplified even further?

    - by Will
    John Resig (of jQuery fame) provides a concise and elegant way to allow simple JavaScript inheritance. It was so short and sweet, in fact, that it inspired me to try and simplify it even further (see code below). I've modified his original function such that it still passes all his tests and has the potential advantage of: readability (50% less code) simplicity (you don't have to be a ninja to understand it) performance (no extra wrappers around super/base method calls) consistency with C#'s base keyword Because this seems almost too good to be true, I want to make sure my logic doesn't have any fundamental flaws/holes/bugs, or if anyone has additional suggestions to improve or refute the code (perhaps even John Resig could chime in here!). Does anyone see anything wrong with my approach (below) vs. John Resig's original approach? if (!window.Class) { window.Class = function() {}; window.Class.extend = function(members) { var prototype = new this(); for (var i in members) prototype[i] = members[i]; prototype.base = this.prototype; function object() { if (object.caller == null && this.initialize) this.initialize.apply(this, arguments); } object.constructor = object; object.prototype = prototype; object.extend = arguments.callee; return object; }; } And the tests (below) are nearly identical to the original ones except for the syntax around base/super method calls (for the reason enumerated above): var Person = Class.extend( { initialize: function(isDancing) { this.dancing = isDancing; }, dance: function() { return this.dancing; } }); var Ninja = Person.extend( { initialize: function() { this.base.initialize(false); }, dance: function() { return this.base.dance(); }, swingSword: function() { return true; } }); var p = new Person(true); alert("true? " + p.dance()); // => true var n = new Ninja(); alert("false? " + n.dance()); // => false alert("true? " + n.swingSword()); // => true alert("true? " + (p instanceof Person && p instanceof Class && n instanceof Ninja && n instanceof Person && n instanceof Class));

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  • Silverlight with MVVM Inheritance: ModelView and View matching the Model

    - by moonground.de
    Hello Stackoverflowers! :) Today I have a special question on Silverlight (4 RC) MVVM and inheritance concepts and looking for a best practice solution... I think that i understand the basic idea and concepts behind MVVM. My Model doesn't know anything about the ViewModel as the ViewModel itself doesn't know about the View. The ViewModel knows the Model and the Views know the ViewModels. Imagine the following basic (example) scenario (I'm trying to keep anything short and simple): My Model contains a ProductBase class with a few basic properties, a SimpleProduct : ProductBase adding a few more Properties and ExtendedProduct : ProductBase adding another properties. According to this Model I have several ViewModels, most essential SimpleProductViewModel : ViewModelBase and ExtendedProductViewModel : ViewModelBase. Last but not least, according Views SimpleProductView and ExtendedProductView. In future, I might add many product types (and matching Views + VMs). 1. How do i know which ViewModel to create when receiving a Model collection? After calling my data provider method, it will finally end up having a List<ProductBase>. It containts, for example, one SimpleProduct and two ExtendedProducts. How can I transform the results to an ObservableCollection<ViewModelBase> having the proper ViewModel types (one SimpleProductViewModel and two ExtendedProductViewModels) in it? I might check for Model type and construct the ViewModel accordingly, i.e. foreach(ProductBase currentProductBase in resultList) if (currentProductBase is SimpleProduct) viewModels.Add( new SimpleProductViewModel((SimpleProduct)currentProductBase)); else if (currentProductBase is ExtendedProduct) viewModels.Add( new ExtendedProductViewModels((ExtendedProduct)currentProductBase)); ... } ...but I consider this very bad practice as this code doesn't follow the object oriented design. The other way round, providing abstract Factory methods would reduce the code to: foreach(ProductBase currentProductBase in resultList) viewModels.Add(currentProductBase.CreateViewModel()) and would be perfectly extensible but since the Model doesn't know the ViewModels, that's not possible. I might bring interfaces into game here, but I haven't seen such approach proven yet. 2. How do i know which View to display when selecting a ViewModel? This is pretty the same problem, but on a higher level. Ended up finally having the desired ObservableCollection<ViewModelBase> collection would require the main view to choose a matching View for the ViewModel. In WPF, there is a DataTemplate concept which can supply a View upon a defined DataType. Unfortunately, this doesn't work in Silverlight and the only replacement I've found was the ResourceSelector of the SLExtensions toolkit which is buggy and not satisfying. Beside that, all problems from Question 1 apply as well. Do you have some hints or even a solution for the problems I describe, which you hopefully can understand from my explanation? Thank you in advance! Thomas

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  • Hierarchy inheritance

    - by reito
    I had faced the problem. In my C++ hierarchy tree I have two branches for entities of difference nature, but same behavior - same interface. I created such hierarchy trees (first in image below). And now I want to work with Item or Base classes independetly of their nature (first or second). Then I create one abstract branch for this use. My mind build (second in image below). But it not working. Working scheme seems (third in image below). It's bad logic, I think... Do anybody have some ideas about such hierarchy inheritance? How make it more logical? More simple for understanding? Image Sorry for my english - russian internet didn't help:) Update: You ask me to be more explicit, and I will be. In my project (plugins for Adobe Framemaker) I need to work with dialogs and GUI controls. In some places I working with WinAPI controls, and some other places with FDK (internal Framemaker) controls, but I want to work throw same interface. I can't use one base class and inherite others from it, because all needed controls - is a hierarchy tree (not one class). So I have one hierarchy tree for WinAPI controls, one for FDK and one abstract tree to use anyone control. For example, there is an Edit control (WinEdit and FdkEdit realization), a Button control (WinButton and FdkButton realization) and base entity - Control (WinControl and FdkControl realization). For now I can link my classes in realization trees (Win and Fdk) with inheritence between each of them (WinControl is base class for WinButton and WinEdit; FdkControl is base class for FdkButton and FdkEdit). And I can link to abstract classes (Control is base class for WinControl and FdkControl; Edit is base class for WinEdit and FdkEdit; Button is base class for WinButton and FdkButton). But I can't link my abstract tree - compiler swears. In fact I have two hierarchy trees, that I want to inherite from another one. Update: I have done this quest! :) I used the virtual inheritence and get such scheme (http://img12.imageshack.us/img12/7782/99614779.png). Abstract tree has only absolute abstract methods. All inheritence in abstract tree are virtual. Link from realization tree to abstract are virtual. On image shown only one realization tree for simplicity. Thanks for help!

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  • validate uniqueness amongst multiple subclasses with Single Table Inheritance

    - by irkenInvader
    I have a Card model that has many Sets and a Set model that has many Cards through a Membership model: class Card < ActiveRecord::Base has_many :memberships has_many :sets, :through => :memberships end class Membership < ActiveRecord::Base belongs_to :card belongs_to :set validates_uniqueness_of :card_id, :scope => :set_id end class Set < ActiveRecord::Base has_many :memberships has_many :cards, :through => :memberships validates_presence_of :cards end I also have some sub-classes of the above using Single Table Inheritance: class FooCard < Card end class BarCard < Card end and class Expansion < Set end class GameSet < Set validates_size_of :cards, :is => 10 end All of the above is working as I intend. What I'm trying to figure out is how to validate that a Card can only belong to a single Expansion. I want the following to be invalid: some_cards = FooCard.all( :limit => 25 ) first_expansion = Expansion.new second_expansion = Expansion.new first_expansion.cards = some_cards second_expansion.cards = some_cards first_expansion.save # Valid second_expansion.save # **Should be invalid** However, GameSets should allow this behavior: other_cards = FooCard.all( :limit => 10 ) first_set = GameSet.new second_set = GameSet.new first_set.cards = other_cards # Valid second_set.cards = other_cards # Also valid I'm guessing that a validates_uniqueness_of call is needed somewhere, but I'm not sure where to put it. Any suggestions? UPDATE 1 I modified the Expansion class as sugested: class Expansion < Set validate :validates_uniqueness_of_cards def validates_uniqueness_of_cards membership = Membership.find( :first, :include => :set, :conditions => [ "card_id IN (?) AND sets.type = ?", self.cards.map(&:id), "Expansion" ] ) errors.add_to_base("a Card can only belong to a single Expansion") unless membership.nil? end end This works when creating initial expansions to validate that no current expansions contain the cards. However, this (falsely) invalidates future updates to the expansion with new cards. In other words: old_exp = Expansion.find(1) old_exp.card_ids # returns [1,2,3,4,5] new_exp = Expansion.new new_exp.card_ids = [6,7,8,9,10] new_exp.save # returns true new_exp.card_ids << [11,12] # no other Expansion contains these cards new_exp.valid? # returns false ... SHOULD be true

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  • Conceptual inheritance implementation

    - by TheSENDER
    Hi there, I'm writing a spatial data structure and I have a doubt about what's the best NODE implementation. According to my design I have an abstract node entity and three classes which inherit from it: EMPTYNODE, FULLNODE, INTERNALNODE. The first one has no particular data. The second one has 1 reference to a generic element. The third one has 2 references to other nodes. I have found several ways to implement this situation (that I have already coded) but I can't decide what's the best. The first solution that I have found is to use a single class Node that potentially performs all the operation in this way: private static class Node { private Elem elem = null; private Node left = null, right = null; public Elem getElem() { assert isFull(); return elem; } public boolean isEmpty() { return elem == null && left == null; } public boolean isFull() { return elem != null; } public boolean isInternal() { return elem == null && left != null; } } The second solution is to write an explicit division by classes where every class offers only its methods. Obviously in this way we are obliged to perform several casts to the node objects. private static abstract class Node { public abstract boolean isEmpty(); public abstract boolean isFull(); public abstract boolean isInternal(); } private static class FullNode extends Node{ private ITriangle elem; @Override public boolean isEmpty() { return false; } @Override public final boolean isFull() { return true; } @Override public final boolean isInternal() { return false; } public Elem getElem() { return elem; } } The third one solution is to use the inheritance allowing every classes to offer all the methods, but the object type should by check by "isEmpty()" and similar methods. In case of wrong call we'll throw an exception. private static abstract class Node { public abstract boolean isEmpty(); public abstract boolean isFull(); public abstract boolean isInternal(); public abstract Elem getElem(); } private static class Empty extends Node{ @Override public boolean isEmpty() { return true; } @Override public final boolean isFull() { return false; } @Override public final boolean isInternal() { return false; } @Override public Elem getElem() { throw new AssertionError(); } } What do you think about these three solutions? Which one would you use? Any other ideas? Thanks for your help. Every idea will be appreciated.

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  • Does this inheritance design belong in the database?

    - by Berryl
    === CLARIFICATION ==== The 'answers' older than March are not answers to the question in this post! Hello In my domain I need to track allocations of time spent on Activities by resources. There are two general types of Activities of interest - ones base on a Project and ones based on an Account. The notion of Project and Account have other features totally unrelated to both each other and capturing allocations of time, and each is modeled as a table in the database. For a given Allocation of time however, it makes sense to not care whether the allocation was made to either a Project or an Account, so an ActivityBase class abstracts away the difference. An ActivityBase is either a ProjectActivity or an AccountingActivity (object model is below). Back to the database though, there is no direct value in having tables for ProjectActivity and AccountingActivity. BUT the Allocation table needs to store something in the column for it's ActivityBase. Should that something be the Id of the Project / Account or a reference to tables for ProjectActivity / Accounting? How would the mapping look? === Current Db Mapping (Fluent) ==== Below is how the mapping currently looks: public class ActivityBaseMap : IAutoMappingOverride<ActivityBase> { public void Override(AutoMapping<ActivityBase> mapping) { //mapping.IgnoreProperty(x => x.BusinessId); //mapping.IgnoreProperty(x => x.Description); //mapping.IgnoreProperty(x => x.TotalTime); mapping.IgnoreProperty(x => x.UniqueId); } } public class AccountingActivityMap : SubclassMap<AccountingActivity> { public void Override(AutoMapping<AccountingActivity> mapping) { mapping.References(x => x.Account); } } public class ProjectActivityMap : SubclassMap<ProjectActivity> { public void Override(AutoMapping<ProjectActivity> mapping) { mapping.References(x => x.Project); } } There are two odd smells here. Firstly, the inheritance chain adds nothing in the way of properties - it simply adapts Projects and Accounts into a common interface so that either can be used in an Allocation. Secondly, the properties in the ActivityBase interface are redundant to keep in the db, since that information is available in Projects and Accounts. Cheers, Berryl ==== Domain ===== public class Allocation : Entity { ... public virtual ActivityBase Activity { get; private set; } ... } public abstract class ActivityBase : Entity { public virtual string BusinessId { get; protected set; } public virtual string Description { get; protected set; } public virtual ICollection<Allocation> Allocations { get { return _allocations.Values; } } public virtual TimeQuantity TotalTime { get { return TimeQuantity.Hours(Allocations.Sum(x => x.TimeSpent.Amount)); } } } public class ProjectActivity : ActivityBase { public virtual Project Project { get; private set; } public ProjectActivity(Project project) { BusinessId = project.Code.ToString(); Description = project.Description; Project = project; } }

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  • Templates, interfaces (multiple inheritance) and static functions (named constructors)

    - by fledgling Cxx user
    Setup I have a graph library where I am trying to decompose things as much as possible, and the cleanest way to describe it that I found is the following: there is a vanilla type node implementing only a list of edges: class node { public: int* edges; int edge_count; }; Then, I would like to be able to add interfaces to this whole mix, like so: template <class T> class node_weight { public: T weight; }; template <class T> class node_position { public: T x; T y; }; and so on. Then, the actual graph class comes in, which is templated on the actual type of node: template <class node_T> class graph { protected: node_T* nodes; public: static graph cartesian(int n, int m) { graph r; r.nodes = new node_T[n * m]; return r; } }; The twist is that it has named constructors which construct some special graphs, like a Cartesian lattice. In this case, I would like to be able to add some extra information into the graph, depending on what interfaces are implemented by node_T. What would be the best way to accomplish this? Possible solution I thought of the following humble solution, through dynamic_cast<>: template <class node_T, class weight_T, class position_T> class graph { protected: node_T* nodes; public: static graph cartesian(int n, int m) { graph r; r.nodes = new node_T[n * m]; if (dynamic_cast<node_weight<weight_T>>(r.nodes[0]) != nullptr) { // do stuff knowing you can add weights } if (dynamic_cast<node_position<positionT>>(r.nodes[0]) != nullptr) { // do stuff knowing you can set position } return r; } }; which would operate on node_T being the following: template <class weight_T, class position_T> class node_weight_position : public node, public node_weight<weight_T>, public node_position<position_T> { // ... }; Questions Is this -- philosophically -- the right way to go? I know people don't look nicely at multiple inheritance, though with "interfaces" like these it should all be fine. There are unfortunately problems with this. From what I know at least, dynamic_cast<> involves quite a bit of run-time overhead. Hence, I run into a problem with what I had solved earlier: writing graph algorithms that require weights independently of whether the actual node_T class has weights or not. The solution with this 'interface' approach would be to write a function: template <class node_T, class weight_T> inline weight_T get_weight(node_T const & n) { if (dynamic_cast<node_weight<weight_T>>(n) != nullptr) { return dynamic_cast<node_weight<weight_T>>(n).weight; } return T(1); } but the issue with it is that it works using run-time information (dynamic_cast), yet in principle I would like to decide it at compile-time and thus make the code more efficient. If there is a different solution that would solve both problems, especially a cleaner and better one than what I have, I would love to hear about it!

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  • C#: Inheritance, Overriding, and Hiding

    - by Rosarch
    I'm having difficulty with an architectural decision for my C# XNA game. The basic entity in the world, such as a tree, zombie, or the player, is represented as a GameObject. Each GameObject is composed of at least a GameObjectController, GameObjectModel, and GameObjectView. These three are enough for simple entities, like inanimate trees or rocks. However, as I try to keep the functionality as factored out as possible, the inheritance begins to feel unwieldy. Syntactically, I'm not even sure how best to accomplish my goals. Here is the GameObjectController: public class GameObjectController { protected GameObjectModel model; protected GameObjectView view; public GameObjectController(GameObjectManager gameObjectManager) { this.gameObjectManager = gameObjectManager; model = new GameObjectModel(this); view = new GameObjectView(this); } public GameObjectManager GameObjectManager { get { return gameObjectManager; } } public virtual GameObjectView View { get { return view; } } public virtual GameObjectModel Model { get { return model; } } public virtual void Update(long tick) { } } I want to specify that each subclass of GameObjectController will have accessible at least a GameObjectView and GameObjectModel. If subclasses are fine using those classes, but perhaps are overriding for a more sophisticated Update() method, I don't want them to have to duplicate the code to produce those dependencies. So, the GameObjectController constructor sets those objects up. However, some objects do want to override the model and view. This is where the trouble comes in. Some objects need to fight, so they are CombatantGameObjects: public class CombatantGameObject : GameObjectController { protected new readonly CombatantGameModel model; public new virtual CombatantGameModel Model { get { return model; } } protected readonly CombatEngine combatEngine; public CombatantGameObject(GameObjectManager gameObjectManager, CombatEngine combatEngine) : base(gameObjectManager) { model = new CombatantGameModel(this); this.combatEngine = combatEngine; } public override void Update(long tick) { if (model.Health <= 0) { gameObjectManager.RemoveFromWorld(this); } base.Update(tick); } } Still pretty simple. Is my use of new to hide instance variables correct? Note that I'm assigning CombatantObjectController.model here, even though GameObjectController.Model was already set. And, combatants don't need any special view functionality, so they leave GameObjectController.View alone. Then I get down to the PlayerController, at which a bug is found. public class PlayerController : CombatantGameObject { private readonly IInputReader inputReader; private new readonly PlayerModel model; public new PlayerModel Model { get { return model; } } private float lastInventoryIndexAt; private float lastThrowAt; public PlayerController(GameObjectManager gameObjectManager, IInputReader inputReader, CombatEngine combatEngine) : base(gameObjectManager, combatEngine) { this.inputReader = inputReader; model = new PlayerModel(this); Model.Health = Constants.PLAYER_HEALTH; } public override void Update(long tick) { if (Model.Health <= 0) { gameObjectManager.RemoveFromWorld(this); for (int i = 0; i < 10; i++) { Debug.WriteLine("YOU DEAD SON!!!"); } return; } UpdateFromInput(tick); // .... } } The first time that this line is executed, I get a null reference exception: model.Body.ApplyImpulse(movementImpulse, model.Position); model.Position looks at model.Body, which is null. This is a function that initializes GameObjects before they are deployed into the world: public void Initialize(GameObjectController controller, IDictionary<string, string> data, WorldState worldState) { controller.View.read(data); controller.View.createSpriteAnimations(data, _assets); controller.Model.read(data); SetUpPhysics(controller, worldState, controller.Model.BoundingCircleRadius, Single.Parse(data["x"]), Single.Parse(data["y"]), bool.Parse(data["isBullet"])); } Every object is passed as a GameObjectController. Does that mean that if the object is really a PlayerController, controller.Model will refer to the base's GameObjectModel and not the PlayerController's overriden PlayerObjectModel? In response to rh: This means that now for a PlayerModel p, p.Model is not equivalent to ((CombatantGameObject)p).Model, and also not equivalent to ((GameObjectController)p).Model. That is exactly what I do not want. I want: PlayerController p; p.Model == ((CombatantGameObject)p).Model p.Model == ((GameObjectController)p).Model How can I do this? override?

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  • Can I change properties of inherited controls at design time?

    - by Jeff Stock
    I am using visual inheritance and was wondering if there is a way to change the properties of inherited controls at design time, preferably in the form designer. If not, then in the designer code. I have my control declared as Public in the base class. I can access it in the child form code, but not in the form designer. Is this just not possible?

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  • Inaccessible item using C++ inheritance

    - by shinjuo
    I am working on C++ project that uses inheritance. I seem to have an error in visual studio in the below file administrator.h. It says that salariedemploye:salary on line 17 is inaccessible and I am not sure why. Admin.cpp #include namespace SavitchEmployees { Administrator::Administrator( ):SalariedEmployee(), salary(0) { //deliberately empty } Administrator::Administrator(const string& theName, const string& theSsn, double theAnnualSalary) :SalariedEmployee(theName, theSsn),salary(theAnnualSalary) { //deliberately empty } void Administrator::inputAdminData() { cout << " Enter the details of the administrator " << getName() << endl; cout << " Enter the admin title" << endl; getline(cin, adminTitle); cout << " Enter the area of responsibility " << endl; getline(cin, workingArea); cout << " Enter the immediate supervisor's name " << endl; getline(cin, supervisorName); } void Administrator::outputAdminData() { cout << "Name: " << getName() << endl; cout << "Title: " << adminTitle << endl; cout << "Area of responsibility: " << workingArea << endl; cout << "Immediate supervisor: " << supervisorName << endl; } void Administrator::printCheck() { setNetPay(salary); cout << "\n___________________________________\n" << "Pay to the order of " << getName() << endl << "The sum of" << getNetPay() << "Dollars\n" << "______________________________________\n" << "Check Stub Not negotiable \n" << "Employee Number: " << getSsn() << endl << "Salaried Employee(Administrator). Regular Pay: " << salary << endl << "______________________________________\n"; } } admin.h #include <iostream> #include "salariedemployee.h" using std::endl; using std::string; namespace SavitchEmployees { class Administrator : public SalariedEmployee { public: Administrator(); Administrator(const string& theName, const string& theSsn, double salary); double getSalary() const; void inputAdminData(); void outputAdminData(); void printCheck(); private: string adminTitle;//administrator's title string workingArea;//area of responsibility string supervisorName;//immediate supervisor }; } #endif SalariedEmployee.cpp namespace SavitchEmployees { SalariedEmployee::SalariedEmployee():Employee(),salary(0) { //deliberately empty } SalariedEmployee::SalariedEmployee(const string& theName, const string& theNumber, double theWeeklyPay) :Employee(theName, theNumber), salary(theWeeklyPay) { //deliberately empty } double SalariedEmployee::getSalary() const { return salary; } void SalariedEmployee::setSalary(double newSalary) { salary = newSalary; } void SalariedEmployee::printCheck() { setNetPay(salary); cout << "\n___________________________________\n" << "Pay to the order of " << getName() << endl << "The sum of" << getNetPay() << "Dollars\n" << "______________________________________\n" << "Check Stub NOT NEGOTIABLE \n" << "Employee Number: " << getSsn() << endl << "Salaried Employee. Regular Pay: " << salary << endl << "______________________________________\n"; } } Salariedemplyee.h #ifndef SALARIEDEMPLOYEE_H #define SALARIEDEMPLOYEE_H #include <string> #include "employee.h" namespace SavitchEmployees{ class SalariedEmployee : public Employee{ public: SalariedEmployee(); SalariedEmployee(const string& theName, const string& theSsn, double theWeeklySalary); double getSalary() const; void setSalary(double newSalary); void printCheck(); private: double salary; }; } #endif employee.cpp namespace SavitchEmployees { Employee::Employee():name("No name yet"),ssn("No number yet"),netPay(0){} Employee::Employee(const string& theName, const string& theSsn):name(theName),ssn(theSsn),netPay(0){} string Employee::getName() const { return name; } string Employee::getSsn() const { return ssn; } double Employee::getNetPay() const { return netPay; } void Employee::setName(const string& newName) { name = newName; } void Employee::setSsn(const string& newSsn) { ssn = newSsn; } void Employee::setNetPay(double newNetPay) { netPay = newNetPay; } void Employee::printCheck() const { cout << "\nERROR: pringCheck function called for an \n" << "Undifferentiated employee. Aborting the program!\n" << "Check with the author of this program about thos bug. \n"; exit(1); } }

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  • java inheritance keyword super()

    - by gucciv12
    requirement: Given the class 'ReadOnly' with the following behavior: A (protected) integer instance variable named 'val'. A constructor that accepts an integer and assigns the value of the parameter to the instance variable 'val'. A method name 'getVal' that returns the value of 'val'. Write a subclass named 'ReadWrite' with the following additional behavior: Any necessary constructors. a method named 'setVal' that accepts an integer parameter and assigns it the the 'val' instance variable. a method 'isDirty' that returns true if the setVal method was used to override the value of the 'val' variable. Code class ReadWrite extends ReadOnly { super(int val); void setVal(int val){this.val = val;} boolean isDirty() {if (setVal()(return true)) else return false;}} More Hints: ?     You should be using: modified ?     You should be using: private ?     You should be using: public

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  • [PHP] Singleton class and using inheritance

    - by Saif Bechan
    I have am working on a web application that makes use of helper classes. These classes hold functions to various operation such as form handling. Sometimes I need these classes at more than one spot in my application, The way I do it now is to make a new Object. I can't pass the variable, this will be too much work. I was wondering of using singleton classes for this. This way I am sure only one instance is running at a time. My question however is when I use this pattern, should I make a singleton class for all the objects, this would b a lot of code replication. Could I instead make a super class of superHelper, which is a singleton class, and then let every helper extend it. Would this sort of set up work, or is there another alternative? And if it works, does someone have any suggestions on how to code such a superHelper class. Thank you guys

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  • Inheritance of templates in WPF

    - by Alxandr
    I'm trying to make sure that every child of a given element (MPF.MWindow) gets custom templates. For instance, the button should get the template defined in resMButton.xaml. As of now I'm using the following code on: (resMWindow.xaml) <ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:local="clr-namespace:MPF"> <Style x:Key="SystemKeyAnimations" TargetType="{x:Type Button}"> <Setter Property="Opacity" Value="0.5" /> <Setter Property="Background" Value="Transparent" /> <Style.Triggers> <EventTrigger RoutedEvent="Mouse.MouseEnter"> <BeginStoryboard> <Storyboard> <DoubleAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetProperty="Opacity"> <SplineDoubleKeyFrame KeyTime="00:00:00.2" Value="1.0" /> </DoubleAnimationUsingKeyFrames> </Storyboard> </BeginStoryboard> </EventTrigger> <EventTrigger RoutedEvent="Mouse.MouseLeave"> <BeginStoryboard> <Storyboard> <DoubleAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetProperty="Opacity"> <SplineDoubleKeyFrame KeyTime="00:00:00.2" Value="0.5" /> </DoubleAnimationUsingKeyFrames> </Storyboard> </BeginStoryboard> </EventTrigger> </Style.Triggers> </Style> <Style TargetType="{x:Type local:MWindow}"> <!-- Remove default frame appearance --> <Setter Property="WindowStyle" Value="None" /> <Setter Property="AllowsTransparency" Value="True" /> <Setter Property="Background" Value="Transparent" /> <Setter Property="Template"> <Setter.Value> <ControlTemplate TargetType="{x:Type local:MWindow}"> <Border Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" x:Name="ChromeBorder"> <Grid> <Grid.ColumnDefinitions> <ColumnDefinition Width="4" /> <ColumnDefinition /> <ColumnDefinition Width="4" /> </Grid.ColumnDefinitions> <Grid.RowDefinitions> <RowDefinition Height="4" /> <RowDefinition /> <RowDefinition Height="4" /> </Grid.RowDefinitions> <Thumb Grid.Row="0" Grid.Column="1" x:Name="TopThumb" Cursor="SizeNS" BorderThickness="4" BorderBrush="Transparent" /> <Thumb Grid.Row="2" Grid.Column="1" x:Name="BottomThumb" Cursor="SizeNS" BorderThickness="4" BorderBrush="Transparent" /> <Thumb Grid.Row="1" Grid.Column="0" x:Name="LeftThumb" Cursor="SizeWE" BorderThickness="4" BorderBrush="Transparent" /> <Thumb Grid.Row="1" Grid.Column="2" x:Name="RightThumb" Cursor="SizeWE" BorderThickness="4" BorderBrush="Transparent" /> <Thumb Grid.Row="0" Grid.Column="0" x:Name="TopLeftThumb" Cursor="SizeNWSE" BorderThickness="5" BorderBrush="Transparent" /> <Thumb Grid.Row="0" Grid.Column="2" x:Name="TopRightThumb" Cursor="SizeNESW" BorderThickness="5" BorderBrush="Transparent" /> <Thumb Grid.Row="2" Grid.Column="0" x:Name="BottomLeftThumb" Cursor="SizeNESW" BorderThickness="5" BorderBrush="Transparent" /> <Thumb Grid.Row="2" Grid.Column="2" x:Name="BottomRightThumb" Cursor="SizeNWSE" BorderThickness="5" BorderBrush="Transparent" /> <Grid Grid.Row="1" Grid.Column="1"> <Grid.RowDefinitions> <RowDefinition Height="20" /> <RowDefinition /> </Grid.RowDefinitions> <Grid> <Grid.ColumnDefinitions> <ColumnDefinition /> <ColumnDefinition Width="Auto" /> </Grid.ColumnDefinitions> <StackPanel Orientation="Horizontal" Grid.Column="1"> <Button Command="local:WindowCommands.Minimize" Style="{StaticResource ResourceKey=SystemKeyAnimations}"> <Button.Template> <ControlTemplate> <Canvas Width="10" Height="10" Margin="5" Background="Transparent"> <Line X1="0" X2="10" Y1="5" Y2="5" Stroke="White" StrokeThickness="2" /> </Canvas> </ControlTemplate> </Button.Template> </Button> <Button Command="local:WindowCommands.Maximize" x:Name="MaximizeButton" Style="{StaticResource ResourceKey=SystemKeyAnimations}"> <Button.Template> <ControlTemplate> <Canvas Width="10" Height="10" Margin="5" Background="Transparent"> <Rectangle Width="10" Height="10" Stroke="White" StrokeThickness="2" /> </Canvas> </ControlTemplate> </Button.Template> </Button> <Button Command="ApplicationCommands.Close" Style="{StaticResource ResourceKey=SystemKeyAnimations}"> <Button.Template> <ControlTemplate> <Canvas Width="10" Height="10" Margin="5" Background="Transparent"> <Line X1="0" X2="10" Y1="0" Y2="10" Stroke="White" StrokeThickness="2" /> <Line X1="10" X2="0" Y1="0" Y2="10" Stroke="White" StrokeThickness="2" /> </Canvas> </ControlTemplate> </Button.Template> </Button> </StackPanel> <ContentControl x:Name="TitleContentControl"> <TextBlock Text="{TemplateBinding Title}" Foreground="DarkGray" Margin="5,0" /> </ContentControl> </Grid> <ContentPresenter Content="{TemplateBinding Content}" Grid.Row="1"> <ContentPresenter.Resources> <ResourceDictionary> <ResourceDictionary.MergedDictionaries> <ResourceDictionary Source="/MPF;component/Themes/resMWindowContent.xaml" /> </ResourceDictionary.MergedDictionaries> </ResourceDictionary> </ContentPresenter.Resources> </ContentPresenter> </Grid> </Grid> </Border> </ControlTemplate> </Setter.Value> </Setter> </Style> </ResourceDictionary> As you can see during the ContentPresenter which gets the content of the window I merge in a dicrionary called resMWindowContent.xaml. The resMWindowContent.xaml looks as following: <ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:local="clr-namespace:MPF"> <ResourceDictionary.MergedDictionaries> <ResourceDictionary Source="/MPF;component/Themes/resMButton.xaml" /> </ResourceDictionary.MergedDictionaries> </ResourceDictionary> It simply merges in the resMButton.xaml dictionary (this is done because in the feature I will have MTextBox, mList... and I want to separate them). The resMButton.xaml looks as following: <ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:local="clr-namespace:MPF"> <Style TargetType="{x:Type Button}"> <Setter Property="Template"> <Setter.Value> <ControlTemplate TargetType="{x:Type Button}"> <Grid Background="Transparent"> <Rectangle Stroke="{TemplateBinding BorderBrush}" StrokeThickness="{TemplateBinding BorderThickness}" Fill="{TemplateBinding Background}" /> <ContentPresenter Content="{TemplateBinding Content}" Margin="3" /> </Grid> </ControlTemplate> </Setter.Value> </Setter> </Style> </ResourceDictionary> A simple template drawing a square button. However, it isn't applied at all. My buttons remain normal, and I don't understand what I'm doing wrong. I just want every button inside the MWindow to get a special style (and in time every textbox and so forth). How do I achieve this? One note though: It's important that the styles doesn't apply to elements outside an MWindow.

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  • C# Interface Inheritance (Basics)

    - by anton
    Why does the following produce a compiler error: public interface OwnSession : ISession { } [...] OwnSession s = SessionFactory.OpenSession(); // compiler error (in german unfortunately) [...] "SessionFactory" returns a "ISession" on "OpenSession()" (NHibernate)

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  • Python: Inheritance of a class attribute (list)

    - by Sano98
    Hi everyone, inheriting a class attribute from a super class and later changing the value for the subclass works fine: class Unit(object): value = 10 class Archer(Unit): pass print Unit.value print Archer.value Archer.value = 5 print Unit.value print Archer.value leads to the output: 10 10 10 5 which is just fine: Archer inherits the value from Unit, but when I change Archer's value, Unit's value remains untouched. Now, if the inherited value is a list, the shallow copy effect strikes and the value of the superclass is also affected: class Unit(object): listvalue = [10] class Archer(Unit): pass print Unit.listvalue print Archer.listvalue Archer.listvalue[0] = 5 print Unit.listvalue print Archer.listvalue Output: 10 10 5 5 Is there a way to "deep copy" a list when inheriting it from the super class? Many thanks Sano

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  • Tricky model inheritance - Django

    - by RadiantHex
    Hi folks, I think this is a bit tricky, at least for me. :) So I have 4 models Person, Singer, Bassist and Ninja. Singer, Bassist and Ninja inherit from Person. The problem is that each Person can be any of its subclasses. e.g. A person can be a Singer and a Ninja. Another Person can be a Bassist and a Ninja. Another one can be all three. How should I organise my models? Help would be much appreciated!

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  • problem with template inheritance

    - by amiad
    I'm trying to understand whay i get an error on this code: (the error is under g++ unix compiler. VS is compiling OK) template<class T> class A { public: T t; public: A(const T& t1) : t(t1) {} virtual void Print() const { cout<<*this<<endl;} friend ostream& operator<<(ostream& out, const A<T>& a) { out<<"I'm "<<typeid(a).name()<<endl; out<<"I hold "<<typeid(a.t).name()<<endl; out<<"The inner value is: "<<a.t<<endl; return out; } }; template<class T> class B : public A<T> { public: B(const T& t1) : A<T>(t1) {} const T& get() const { return t; } }; int main() { A<int> a(9); a.Print(); B<A<int> > b(a); b.Print(); (b.get()).Print(); return 0; } This code is giving the following error: main.cpp: In member function 'const T& B::get() const': main.cpp:23: error: 't' was not declared in this scope It did compiled when i changed the code of B to this: template<class T> class B : public A<T> { public: B(const T& t1) : A<T>(t1) {} const T& get() const { return A<T>::t; } }; I just cant understand what is the problem with the first code... It doesn't make sense that i really need to write "A::" every time...

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  • Misunderstanding I have about javascript prototype inheritance

    - by Ilya
    Simple questions. function p() { function A() { this.random = "random"; } A.prototype.newfunc = function(){ alert("5");} function B() { } B.prototype = new A(); var bObj = new B(); } Q1: When I set B's prototype, I don't get how B's prototype property will update when/if A's prototype is updated. I mean, to me it just inherits/copies all those properties. It's not like it's: B.prototype = A.prototype where B and A are one in the same. Q2: After A is being returned and intialized to the prototype object of B, how does JS know not to include that prototype property? What I mean is, we never have this type of situation occuring as the JS interpreter knows just to chop off the property of A's prototype: B.prototype = new A(); //any A object has an associated prototype object B.prototype.prototype;//after initialization we no longer have the separate prototype property of A

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