I am attempting to do something similar to:
public interface IView<T> : T where T : class
{
T SomeParam {get;}
}
So that i can later do
public class SomeView : IView<ISomeView>
{
}
Is it possible to specify inheritance using generics in this way or do i have to go the long way round and explicitly specify both interfaces when defining the class and do:
public interface IView<T>
{
T SomeParam {get;}
}
public class SomeView : IView<ISomeView>, ISomeView
{
}
This isn't possible, but your goal may be achievable with conversion operators. It seems that what you're trying to do is make it possible to pass an IView<T> as the T object which it contains. You could write a base class like this:
public abstract class ViewBase<T> {
public abstract T SomeParam { get; }
public static implicit operator T(ViewBase<T> view) {
return view.SomeParam;
}
}
Then, if you define a class like:
public class SomeView : ViewBase<ISomeView> { }
It can be accepted anywhere an ISomeView is expected:
ISomeView view = new SomeView();
Short answer: It is not possible. See this post
An Interface can't derive from a class. However nothing prevent you from doing this:
public interface ISomeView
{
}
public interface IView<out T> where T:class
{
T SomeParam { get; }
}
public class SomeView:IView<ISomeView>
{
public ISomeView SomeParam { get; set; }
}
Edit:
If you don't want to implement the T SomeParam { get; } each time you need to have an implementation, Does this would work?
public interface ISomeView
{
}
public abstract class BaseView<T> where T : class
{
public T SomeParam { get; set; }
}
public class SomeView : BaseView<ISomeView>{
}
In both case this would work:
public class main
{
public class OneOfThoseView : ISomeView
{
}
public main()
{
OneOfThoseView oneOfThose = new OneOfThoseView();
SomeView x = new SomeView();
x.SomeParam = oneOfThose;
}
}
Edit 2:
Not exactly what you want to do but this would force your SomeView class to return a BaseView<SomeView> class
public interface ISomeView
{
}
public abstract class BaseView<T> where T : BaseView<T>
{
public T SomeParam { get; set; }
}
public class SomeView : BaseView<SomeView>
{
}
Now only this would work.
public main()
{
SomeView y= new SomeView ();
SomeView x = new SomeView();
x.SomeParam = y;
}
Related
I have some problem I can not resolve.
I have a class GlobalTest derived from GlobalObjectImpl:
public class GlobalTest : GlobalObjectImpl
{
public string LastProcessDay { get; set; }
}
It was called from this:
var global = GlobalTest.Get<GlobalTest>();
The GlobalObjectImpl is declared like this:
public abstract class GlobalObjectImpl
{
public bool Save()
{
return DataStore.SaveGlobal(this);
}
public static T Get<T>() where T : GlobalObjectImpl
{
return DataStore.GetGlobal<T>();
}
}
I want to get my LastProceedDate like this:
var global = GlobalTest.Get();
But it fails.
You can make your abstract class generic like the following:
public abstract class Base<T>
{
public static T Get() => throw new NotImplementedException();
}
public class Derived : Base<Derived> { }
And then just call Get
var foo = Derived.Get();
I all, big thank to you, i have succesfully implemented my class
My Abstract Class
public abstract class GlobalTreeObjectImpl<T>
{
public bool Save()
{
return NeoStore.SaveGlobal(this);
}
public static T Get() => NeoStore.GetGlobal<T>();
}
}
Class use abstract class
public class GlobalTest : GlobalTreeObjectImpl<GlobalAntai>
{
public string LastProcessDay { get; set; }
}
Usage of this on my code
var global = GlobalTest.Get();
LoggerManager.LogInfo($"Global LastProcessDay : {global.LastProcessDay} - {DateTime.UtcNow}");
global.LastProcessDay = DateTime.Now.AddDays(10).ToString("yyyy-MM-ddThhh:mmm:ssZ");
global.Save();
global = GlobalTest.Get();
LoggerManager.LogInfo($"Global LastProcessDay : {global.LastProcessDay} - {DateTime.UtcNow}");
I need to create a dll file which contains all the interfaces of the classes but doesn't contain any class.
Because I use these interfaces for a lot of classes it's must be like that:
public interface IClassA
{
string Word { get; }
}
public interface ITest<TClassA> where TClassA : IClassA
{
TClassA A { get; }
}
Example of two classes that implements these interfaces the way I want:
public class ClassA : IClassA
{
public string Word
{
get;
private set;
}
public string Sentence
{
get;
private set;
}
public ClassA(string word, string sentence)
{
this.Word = word;
this.Sentence = sentence;
}
}
public class Test : ITest<ClassA>
{
public ClassA A
{
get;
private set;
}
public Test(ClassA a)
{
this.A = a;
}
}
And I want to do something like that in the main program:
public static void Main(string[] args)
{
ClassA a = new ClassA("hey", "hey world!");
Test t = new Test(a);
Print((ITest<IClassA>)t);
}
public static void Print(ITest<IClassA> t)
{
Console.WriteLine(t.A.Word);
}
But this casting: (ITest<IClassA>)t makes a run time error.
How can I solve it?
thanks!
You should declare Test as
public class Test : ITest<IClassA>
instead of ITest<ClassA>.
Or declare ITest<TClassA> to be covariant on TClassA:
public interface ITest<out TClassA> where TClassA : IClassA
The Test-class implements the concrete ClassA (public class Test : ITest<ClassA>).
So you're trying to cast an ITest<ClassA> to ITest<IClassA> which obviously fails.
If you let the Test-class implement IClassA, the cast works:
public class Test : ITest<IClassA>
{
public IClassA A
{
get; private set;
}
public Test(IClassA a)
{
this.A = a;
}
}
I'm trying to create instance of class Bar but I'm receiving an error:
"Cannot implicitly convert type ConsoleApplication1.Bar to
ConsoleApplication1.BaseFoo<ConsoleApplication1.baseOutput,
ConsoleApplication1.baseInput>"
Any idea what I'm missing or what I'm doing wrong? Any advice will be nice.
public class baseOutput
{
public string output;
}
public class baseInput
{
public string input;
}
public class ExtendOutput : baseOutput
{
public long id;
}
public class ExtendInput : baseInput
{
public long id;
}
public class BaseFoo<baseOutput, baseInput>
{
protected virtual void DoSmth()
{
}
}
public class Bar : BaseFoo<ExtendOutput, ExtendInput>
{
protected override void DoSmth()
{
base.DoSmth();
}
}
public class Test
{
public void Show()
{
}
private BaseFoo<baseOutput, baseInput> CreateInstance()
{
return new Bar(); // Error right here
}
}
I'll give you an example of why you're prevented from doing that.
Imagine instead, your classes were written like this:
public class BaseFoo<TOutput, TInput>
where TOutput : BaseOutput
{
public TOutput Something { get; set; }
}
public class Bar : BaseFoo<ExtendOutput, ExtendInput>
{
}
public class BaseInput { }
public class BaseOutput { }
public class ExtendOutput : BaseOutput { }
public class SomethingElse : BaseOutput { }
Now, you have this method:
private BaseFoo<BaseOutput, BaseInput> CreateInstance()
{
//At this point, Something will be of type ExtendOutput.
return new Bar();
}
So, we call it like this:
var myBar = CreateInstance();
Now, mybar.Something is of type BaseOutput. That's fine, though, because ExtendOutput : BaseOutput, right? Not quite.
What happens when we do this:
myBar.Something = new SomethingElse();
That's valid, because Something expects a BaseOutput, and SomethingElse is a BaseOutput. However, the object is actually a Bar, which explicitly says it should be an ExtendOutput.
The problem is clearer if we attempt to cast it back:
var myBaseFoo = CreateInstance();
myBaseFoo.Something = new SomethingElse();
Bar myBar = (Bar)myBaseFoo;
myBar.Something; // Here, we're told it's going to be an `ExtendOutput`,
// but we get a `SomethingElse`?
That's clearly wrong. And that's why you're prevented from doing what you're trying to do. You can have this behavior with covariance.
Covariance makes it illegal to pass in a TOutput. So, this line
public TOutput Something { get; set; }
Would be invalid. We would only be allowed to expose the getter:
public TOutput Something { get; }
Which alleviates the above problem
Bar is BaseFoo<ExtendOutput, ExtendInput>, and CreateInstance() requires BaseFoo<baseOutput, baseInput> to be returned, so it can't return Bar which is BaseFoo<ExtendOutput, ExtendInput>.
Regardless ExtendOutput inherits baseOutput, when you inherit a generic class the inheritance is invariant.
Consider using interfaces with in and out generic modifiers:
public class baseOutput
{
public string output;
}
public class baseInput
{
public string input;
}
public class ExtendOutput : baseOutput
{
public long id;
}
public class ExtendInput : baseInput
{
public long id;
}
public interface IBaseFoo<out T1, out T2>
{
public void DoSmth();
}
public class Bar : IBaseFoo<ExtendOutput, ExtendInput>
{
public void DoSmth()
{
}
}
public class Test
{
public void Show()
{
}
private IBaseFoo<baseOutput, baseInput> CreateInstance()
{
return new Bar();
}
}
How do I define a factory whose implementations may accept different numbers of parameters?
public abstract class CarFactory
{
public abstract void countStuff(??); //not sure how to define this
}
I would like the factory to be able to create different objects like:
public class BMW : CarFactory
{
public override void countStuff(param1, param2) {}
}
public class Ford : CarFactory
{
public override void countStuff(param1) {}
}
Not sure if "countStuff" should be a factory responsibility, but you could get something similar this way:
public interface ICountParam {}
public class BmwParam : ICountParam
{
public BmwParam(string a)
{
A = a;
}
public string A { get; set; }
}
public class FordParam : ICountParam
{
public FordParam(string a, string b)
{
A = a;
B = b;
}
public string A { get; set; }
public string B { get; set; }
}
public interface ICarFactory<in T> where T : ICountParam
{
void CountStuff(T param);
}
public class BMW : ICarFactory<BmwParam>
{
public void CountStuff(BmwParam param) { }
}
public class Ford : ICarFactory<FordParam>
{
public void CountStuff(FordParam param) { }
}
Usage:
bmw.CountStuff(new BmwParam("A"));
ford.CountStuff(new FordParam("A", "B"));
I want to create a class that could hold any of a number of same type of classes. For example lets says I have a base class like follows:
public class BaseClass
{
public string MyBaseString
{
get;
set;
}
}
And then I have a few derived classes like this:
public class DerivedClass : BaseClass
{
public MyDerivedClassString
{
get;
set;
}
}
public class DerivedClass2 : BaseClass
{
public MyDerivedClass2String
{
get;
set;
}
}
Now I would like a class that accepts one of these implementations and does stuff with it. Here is the only thing I can think of, but there must be a better way:
public class ClassA
{
public object MyClass
{
get;
set;
}
public ClassA (object myClass)
{
MyClass = myClass;
if (object is BaseClass)
{
//do something
}
else if (object is DerivedClass)
{
//do something specific to derived class
}
else if (object is DerivedClass2)
{
//do something specific to derived class 2
}
}
}
CLARIFICATION: The specific goal I am trying to accomplish is to use ClassA as a container class for various implementations of the BaseClass. The business goal I am trying to accomplish is to create a Legend object which might use multiple color schemes (i.e. a Mono Color Ramp, Multi Color Ramp, etc). So I would like the Legend class to contain the ColorScheme that is being used, but still have access to that color scheme's unique properties for modification later on.
CLARIFICATION 2 Based on the wide array of responses I got, I thought I'd provide an exact replication of what I'm trying to do:
public class BaseColorScheme
{
List<Color> _colors = new List<Color>();
public List<Color> Colors
{
get
{
return _colors;
}
set
{
_colors = value;
}
}
}
public class SingleColorScheme : BaseColorScheme
{
public Color MidColor
{
get;
set;
}
public SingleColorScheme( Color midColor, int numberOfClassifications )
{
Colors = CreateMonoColorRamp( midColor, numberOfClassifications );
}
}
public class MultiColorScheme : BaseColorScheme
{
public Color StartColor
{
get;
set;
}
public Color EndColor
{
get;
set;
}
public Color MidColor
{
get;
set;
}
public MultiColorScheme( Color startColor, Color endColor, Color midColor )
{
StartColor = startColor;
EndColor = endColor;
MidColor = midColor;
Colors = //do something to define multi color scheme
}
}
Then I would have a Legend Class that would be something like
public class Legend
{
public object ColorScheme
{ get; set; }
public Guid LegendId
{ get; set; }
public Legend(object colorScheme)
{
ColorScheme = colorScheme;
}
}
Finally I might have a form that sits on top of the legend that displays the properties of the various color schemes based on which type of color scheme it is. Hopefully that helps clarify a bit.
public class ClassA<T> where T : BaseClass
{
public T MyClass { get; set; }
public ClassA(T myClass) { MyClass = myClass; }
}
Beyond that, define the common interface of the class hierarchy either as an interface or as methods (concrete, abstract, or virtual) within the base class. Then you can be assured all derived classes have such method / properties and can use them within your generic wrapper.
Instead of letting ClassA perform whatever needs to be done, you can use polymorphism and let the classes do it to themselves.
Simply declare a virtual method in the base class, have it do whatever you need it do so, and then override this method in the subclasses. In the method in ClassA, you just need to call that method on the object you receive as a parameter - without having to care about the specific type.
If you need to access different properties based on which derived class is passed something like this should help:
public class ClassA<T> where T : BaseClass
{
public T MyClass { get; set; }
public ClassA(T myClass) { MyClass = myClass; }
public void DoStuffToMyClass()
{
if(MyClass is BaseClass)
{ // do base class stuff }
else if(Myclass is DerivedClass)
{ // do DerivedClass stuff }
else if(MyClass is DerivedClass2)
{ // do DerivedClass2 stuff }
}
}
This gives you the type saftey to ensure you at least have the BaseClass object, and possibly a derived class.
The answer is polymorphism, let the object do it themselves.
public class BaseClass
{
public string MyString { get; set; }
public virtual string DoIt()
{
return "I'm Base Class";
}
}
public class DerivedClassA
{
public override string DoIt()
{
return "I'm Derived Class A";
}
}
public class DerivedClassB
{
public override string DoIt()
{
return "I'm Derived Class B";
}
}
....
public ClassA (BaseClass myClass)
{
MyClass = myClass;
MyClass.DoIt();
}
.....
ClassA x1 = ClassA(new BaseClass()) // calls BaseClass.DoIt()
ClassA x2 = ClassA(new DerivedClassA()) // calls DerivedClassA.DoIt()
ClassA x3 = ClassA(new DerivedClassB()) // calls DerivedClassB.DoIt()
whenever you catch yourself acting differently based on the run-time type of the object, you are dealing with code that breaks OO principles, i.e. a class that does not respect the base class contract.
Can you use virtual methods?
public abstract class BaseClass
{
public abstract void DoStuff();
}
public class DerivedClass1 : BaseClass
{
public override void DoStuff()
{
...
}
}
public class DerivedClass2 : BaseClass
{
public override void DoStuff()
{
...
}
}
Without generics:
public class ClassA
{
public BaseClass MyClass
{
get;
set;
}
public ClassA (BaseClass myClass)
{
MyClass = myClass;
myClass.DoStuff();
}
}
or with generics:
public class ClassA<T> where T : BaseClass
{
public T MyClass { get; set; }
public ClassA (T myClass)
{
MyClass = myClass;
myClass.DoStuff();
}
}
Keep it simple: polymorphism
Hopefully your objects have a common interface, something like:
class Base {
public virtual void DoSomething() { /* Default implementation */ }
}
class Derived1 : Base {
public override void DoSomething() { /* Implementation specific to this type */ }
}
class Derived2 : Base {
public override void DoSomething() { /* Another implementation specific to this type */ }
}
Or maybe they implement a common interface. So hopefully your consuming class can hold the most general representation of your inputs as possible and invoke code as such:
class Dependent {
public Dependent(Base instance) {
instance.DoSomething();
}
}
So your Dependent class doesn't really are whether it has a derived type or a base type.
Not quite as simple: visitor pattern
Sometimes polymorphism doesn't really work, which is particularly the case if you need to access the specific members of your derived classes, and those members aren't in the base class. Visitor pattern works well in this case, especially if you have a fixed, well-defined graph of objects.
public interface IVisitor<T> {
T Visit(Base x);
T Visit(Derived1 x);
T Visit(Derived2 x);
}
class Base {
public virtual T Accept<T>(IVisitor<T> visitor) { visitor.Visit(this); }
public string BaseString { get; set; }
}
class Derived1 : Base {
public override T Accept<T>(IVisitor<T> visitor) { visitor.Visit(this); }
public string Derived1String { get; set; }
}
class Derived2 : Base {
public override T Accept<T>(IVisitor<T> visitor) { visitor.Visit(this); }
public string Derived2String { get; set; }
}
So Derived1 and Derived2 have a different set of properties, and if you need to get to those properties without a runtime type-checking, implement a visitor:
class DefaultStringVisitor : IBaseVisitor<string> {
public string Visit(Base x) { return x.BaseString; }
public string Visit(Derived1 x) { return x.Derived1String; }
public string Visit(Derived2 x) { return x.Derived2String; }
}
class Dependent {
public Dependent(Base x) {
string whatever = x.Accept<string>(new DefaultStringVisitor());
}
}
So the visitor pattern gives you access to your derived object's members without a type-check. Its a somewhat inflexible pattern (i.e. need to know which objects to visit up front), but it might work for your needs.