Okay, I have a small hiccup.
I want to implement an interface with a generic parameter type, and then extend that implementation with another parameter type, and not have to do the initialization all over again.
Basically, I have a similar structure to this:
interface IBase<MemberType>;
abstract class Base : IBase<OneMemberType> {
protected OneMemberType member;
public void init() {
member = new OneMemberType();
}
}
class Extended: Base, IBase<AnotherMemberType> {
}
I want class Extended to have a "member" property of the "AnotherMemberType" type.
AnotherMemberType and OneMemberType both implement the same interface.
Any ideas how i could do that, without explicitly defining it in the Extended class?
This is the actual interface.
interface ILayer<TextureProviderType>
{
Texture2D getTexture();
byte[,] getArray();
void generate();
}
Updated
I'm trying to have specific objects that extend the BaseLayer class and that each use a specific TextureProvider child, and only have to instantiate the texture providers in the base class.
Update 2
Okay, it has nothing to do with interfaces apparently. What I want to have is a generic base class member, that can be assigned a type in the extended children classes.
You can implement the interface methods just once and it will work for both interfaces.
If you want different implementations per interface, you must use explicit implementations or use the generic type parameter in the signature of your interface methods.
Point is, you can't have 2 methods with the same signature in your class and have the CLR know which one to use.
Edit: after reading you comment on the problem you're trying to solve:
Wouldn't a generic type parameter in your BaseLayer + inheritance in your TextureProviders work? Would look something like this:
class TextureProvider
{
public TextureProvider()
{
}
public void Foo()
{
}
}
class SpecialTextureProvider : TextureProvider
{
public SpecialTextureProvider()
: base()
{
}
}
class BaseLayer<TP> where TP : TextureProvider, new()
{
public BaseLayer()
{
var tp = new TP();
}
}
class SpecificLayer : BaseLayer<SpecialTextureProvider>
{
}
Alternatively, you could use the factory pattern.
Related
Let's say I create this interface :
interface Equipable
{
public bool Equip(Equipment equipment);
}
Let's just assume our Equipment class is empty for now:
class Equipment
{
}
I create a derived class from Equipment (let's keep it simple):
class Trinkets : Equipment
{
...
public Trinkets(...)
{
...
}
}
Then I want a Trinket class that implements Equipable and that uses its method:
class Trinket : Item, Equipable
{
bool Equipable.Equip(Trinkets trinkets)
{
return true;
}
}
But it seems I can't do this (CS0539), I can't use Trinkets class (which however is Equipment derived class) as a method parameter of my interface.
This didn't work for me and seems far-fetched: Implementation of interface when using child class of a parent class in method of interface.
And it also seems that the above solution does not allow you to use other classes than the base class declared in the interface header.
So my question is simple, is there a way to do what I'm trying to do?
Is it bad practice? If it is, what should I do to overcome this problem?
According to your description that you need an interface that accepts a reference to Equipment. In C#, this means it can accept an object of that class or any derived class on method call. This doesn't include the method implementation.
So Trinket should be declared like this:
class Trinket : Item, Equipable
{
bool Equipable.Equip(Equipment equipment)
{
return true;
}
}
But this allows you to call that method passing it an object of type Equipment or Trinkets as a derived class of Equipment. Here's a simple example on that:
var trs = new Trinkets();
var eq = new Equipment();
var tr = new Trinket();
tr.Equip(trs);
// Or
tr.Equip(eq);
The inheritance will work on object references but not when implementing the method.
On line bool Equipable.Equip(Trinkets trinkets)
You specified in the Equipable interface that all classes that implement Equipable need to contain a defined method called Equip that receive an Equipment parameter and return a bool. The method you defined in the Trinket class receive a Trinket parameter, so it wont satisfy the condition set out by the interface.
I have two base classes BaseObject and BaseObjectSettings. The first defines the object behaviour and the second defines the state of the class (useful for serialisation).
If I want to create a derived BaseObject class with specific settings then I can use a method with a generic type constraint.
public void CreateBaseObjectInstance<T>(BaseObjectSettings baseObjectSettings) where T : BaseObject
{
var instance = pool.GetInstance<T>();
instance.Settings = baseObjectSettings;
scene.Add(instance);
}
The problem I am facing is that while I can constrain the generic type to BaseClass I can't constrain the BaseClassSettings to the relevant derived BaseClass. This means that I can do things like
CreateBaseObjectInstance<Banana>(new AppleSettings());
which seems a bit terrible.
What are my options given that I am currently constrained to both creating and initialising the object in the same method before adding it to the scene?
One way is to have all your settings classes inherit from a generic base class. The generic base class could then inherit from BaseObjectSettings. The generic type parameter indicates what kind of object this settings class is for.
For example, for your AppleSettings,
class AppleSettings: ObjectSettings<Apple> {
...
}
abstract class ObjectSettings<T>: BaseObjectSettings where T: BaseObject {}
Now, you can change CreateBaseObjectInstance to accept an instance of ObjectSettings<T> instead:
public void CreateBaseObjectInstance<T>(ObjectSettings<T> objectSettings) where T : BaseObject
{
var instance = pool.GetInstance<T>();
instance.Settings = objectSettings;
scene.Add(instance);
}
If you pass Banana as T, it would expect ObjectSettings<Banana>, preventing you from giving it AppleSettings, which is ObjectSettings<Apple>.
You need to create a generic interface or base class that where you define the settings type:
public class BaseObject<TSettings>
{
public TSettings Settings { get; set; }
}
Then your method will require two generic arguments - one for the actual object to create TObject and one for method's argument for the settings TSettings. You then constrain TObject to an implementation of the implemented interface or base class/derivation thereof, using generic argument TSettings as the constraint's type's generic argument
public void CreateBaseObjectInstance<TObject, TSettings>(
TSettings settings
)
where TObject : BaseObject<TSettings>
{
...
}
Example (using above BaseObject implementation):
public class MyObjectSettings
{
...
}
public class MyObject : BaseObject<MyObjectSettigns>
{
}
Method call:
var settings = new MyObjectSettings(){ ... };
CreateBaseObjectInstance<MyObject>( settings ); // second generic argument should be inferred
I don't really understand the logic here as things are missing, but from the code provided you can probably write:
public void CreateBaseObjectInstance<TBase, TSettings>(TSettings baseObjectSettings)
where TBase : BaseObject
where TSettings : BaseObjectSettings
Used like that:
CreateBaseObjectInstance<Banana, AppleSettings>(new AppleSettings());
Can be improved to:
public void CreateBaseObjectInstance<TBase, TSettings>(TSettings baseObjectSettings)
where TBase : BaseObject
where TSettings : BaseObjectSettings, new()
{
if ( baseObjectSettings == null ) baseObjectSettings = new TSettings();
...
}
CreateBaseObjectInstance<Banana, AppleSettings>();
But if there is a strong coupling between entity and settings, you should redesign to define dependency with an association using a thing that can also be similar to #Sweeper's and #Moho's answers:
Association, Composition and Aggregation in C#
Understanding the Aggregation, Association, Composition
Generics in .NET
Generic classes and methods
I'm using a C# data visualization library which makes heavy use of generics. Our application needs to build these charts programtically, including changing the series of the chart at runtime. The code looks like this:
builder.Series(series =>
{
if (seriesDefinition.Type == ChartType.Bar) {
series.Bar(data).Name(seriesDefinition.Name);
}
else if (seriesDefinition.Type == ChartType.Area) {
series.Area(data).Name(seriesDefinition.Name);
}
})
Where the Bar() and Area() calls are library methods, and the seriesDefinition object is our own class which contains configuration information about the series we want to create.
Now, our series definition object is going to have many properties besides just the name, and all of them will need to be applied to the series in the builder. To avoid a massive amount of code duplication, we want to store the result of the Bar() or Area() etc. call, so that we can apply the rest of the configurations once outside of the if-else blocks. To do that, we need to declare its specific type. Working backward from the derived return types of those library methods, we get to this parent type which has the methods we need:
public abstract class ChartSeriesBuilderBase<TSeries, TSeriesBuilder> : IHideObjectMembers
where TSeries : IChartSeries
where TSeriesBuilder : ChartSeriesBuilderBase<TSeries, TSeriesBuilder>
{
}
Now I need to declare it with appropriate type arguments:
builder.Series(series =>
{
ChartSeriesBuilderBase<IChartSeries, ???> seriesBuilder = null; // <--
if (seriesDefinition.Type == ChartType.Bar) {
seriesBuilder = series.Bar(data);
}
else if (seriesDefinition.Type == ChartType.Area) {
seriesBuilder = series.Area(data);
}
seriesBuilder.Name(seriesDefinition.Name);
})
What can I replace ??? with that satisfies this type declaration?
Edit: Here is the class hierarchy starting with the return types of Bar() or Area().
// Area() returns this; Bar() returns ChartBarSeriesBuilder
public class ChartAreaSeriesBuilder<T> :
ChartAreaSeriesBuilderBase<IChartAreaSeries, ChartAreaSeriesBuilder<T>>
where T : class
{
}
T is the type of the data item for the series, which I have control over. It's inferred when I pass in an object of that type to Area().
// or ChartBarSeriesBuilderBase
public abstract class ChartAreaSeriesBuilderBase<TSeries, TSeriesBuilder> :
ChartSeriesBuilderBase<TSeries, TSeriesBuilder>
where TSeries : IAreaSeries
where TSeriesBuilder : ChartAreaSeriesBuilderBase<TSeries, TSeriesBuilder>
{
}
and finally
public abstract class ChartSeriesBuilderBase<TSeries, TSeriesBuilder> : IHideObjectMembers
where TSeries : IChartSeries
where TSeriesBuilder : ChartSeriesBuilderBase<TSeries, TSeriesBuilder>
{
}
tl;dr You can't unless ChartSeriesBuilderBase implements some other non-generic interfaces.
You can create a class which inherits from ChartSeriesBuilderBase and then instantiate it and this works, as follows:
public class MyBuilder : ChartSeriesBuilderBase<IChartSeries, MyBuilder>
{
}
It's a bit confusing, but as MyBuilder is being defined, it is able to reference itself as the generic type for its base class.
I would imagine that Bar and Area are also defined in a similar manner and so reference themselves in their own generic definition. As Bar and Area inherit from ChartSeriesBuilderBase, we can declare the following variables:
ChartSeriesBuilderBase<IChartSeries, Bar> myBarBuilder;
ChartSeriesBuilderBase<IChartSeries, Area> myAreaBuilder;
But again, as these variables are typed to either Bar or Area, they don't help us to create a variable capable of containing both object types.
Now consider this similar, but simplified situation:
public class MyGeneric<T>
{
}
void q49156521()
{
var myObject = new MyGeneric<string>();
var myOtherObject = new MyGeneric<int>();
}
While both variables are MyGenerics, there is no base class that I can use to define a variable which would be able to contain both myObject and myOtherObject because they differ by their generic type.
Note that many generic classes allow you to solve this exact problem by implementing non-generic interfaces. For example, such asList<T> implements IList so therefore it is possible to use an IList variable to contain both a List<string> and a List<int>. However, it looks like ChartSeriesBuilderBase has no such interface that could be used.
So I'm afraid it looks like the answer is, you can't.
I had to reference another question here on SO to even know this was a thing: https://stackoverflow.com/a/25166761/8915494
Hope this helps
I have an abstract super class and subclasses inheriting from it.
Each subclass MySubclass shall have a public static MySubclass CreateFrom(ISomething something) factory method. The interface of its argument is the same for all subclasses, but the return type must of course always be the type of the respective subclass.
Can I somehow achieve this to have static factory methods following an interface or abstract superclass method definition without creating a separate static factory class for each single subclass?
If the ISomething is always of the same (or at least a common) type, you could make the CreateFrom method of the superclass generic and Invoke the constructor of the inherited class with the parameter. Just make sure all your inherited classes have that constructor (Not sure but I don't think there is a way to 'force' a constructor pattern).
public abstract class SuperClass
{
public static T CreateFrom(ISomething something)
{
return (T)Activator.CreateInstance(typeof(T), something);
}
}
public class InheritedClass : SuperClass
{
public InheritedClass(ISomething something)
{}
}
This way you can create instances by calling
SuperClass.CreateFrom<InheritedClass>(something);
Or you split the creation and initialization:
public abstract class SuperClass
{
protected abstract void Initialize(ISomething something);
public static T CreateFrom(ISomething something) where T : new()
{
T result = new T();
T.Initialize(something);
}
}
public class InheritedClass : SuperClass
{
public InheritedClass()
{}
protected override Initialize(ISomething something)
{}
}
You can´t define static members on interfaces as static members belong to a certain class. However I can´t imagine of a reason to use this. You should ask yourself why you need such a functionality. Does a sub-class really have to instantiate itself or can the same easily be done with another independent (factory-)class?
Just create one simple factory-class with a generic parameter that indicates what to create.
class Factory<T> where T: new()
{
T CreateFrom(ISomething param)
{
return new T();
}
}
Now you can simply call it like this:
var myFactory = new Factory<MyClass>();
myFactory.CreateFrom(mySomething);
I resorted to a different solution in similiar kind of requirement. In my superclass which happened to be an abstract one I required to create an instance of subclass to do something with it so I did the following trick:
public abstract class Element
{
protected virtual void copyFrom(Element other)
{
}
protected abstract Elememt newInstanceOfMyType();
public object clone()
{
var instance= newInstanceOfMyType();
instance.copyFrom(this);
return instance;
}
}
Now all my subclasses inheriting from Element class required to override newInstanceOfMyType method to give away instance of its type and then also override copyFrom method to produce a perfect clone. Now people might argue that why an abstract Clone method cant do the same job? Yes it can. But I required cloned instance of subclass as well as an empty instance(without copying anything from current) so I came up with this architecture.
I'm trying to create a set of classes with different level of abstraction. I will use the Vector example here.
My goal is that the user of my classes can choose the level of abstraction to use i.e. they may or may not want to be using the more derived class.
interface IVector
{
Vector A();
}
interface ISparseVector : IVector
{
new SparseVector A();
}
Now, I implement the classes as such:
class Vector : IVector
{
public Vector A() { return new Vector(); }
}
class SparseVector : Vector,ISparseVector
{
public new SparseVector A() { return new SparseVector(); }
}
This is all fine and dandy. However, when the base class is abstract such as:
abstract class Vector : IVector
{
public abstract Vector A();
}
class SparseVector : Vector,ISparseVector
{
public SparseVector A() { return new SparseVector(); } // Hides abstract member.
}
I get a compile error saying that the derived method is hiding the abstract method in Vector. Any idea of how to get around this?
The feature you want is called "return type covariance", and it is not a feature of C#. Return type covariance is the feature where you can have a virtual method that return an Animal, and then you override that with a method that returns a Giraffe.
Doing so is typesafe and some languages do have this feature -- C++ for example -- but C# does not and we have no plans to add it. Your overriding method has to be marked override, and it has to match exactly -- in name, formal parameter types, and return type.
The reason is in your first example on the Vector class, you weren't specifying an access level for the A() method. This means it is a private method, which is the default. You could use the new keyword in the SparseVector class to get around this error.
For a start, you should look at this thread which specifies why you cannot have an abstract constructor.
Why can't I create an abstract constructor on an abstract C# class?
Then, you should put an abstract method in your Vector class that can actually be overridden to provide implementation, as abstract methods are supposed to be.
You can't mix abstract and interface methods the way you're trying. If you were to declare 'Vector' abstract and override the implementation of A(), you'd be overriding 'Vector A()' from your abstract class, but that wouldn't implement the interface ISparseVector.Vector, which has a return type of ISparseVector.
Your use-case doesn't appear to require that 'Vector' be abstract.