This is a long shot, but I have a funny coding situation where I want the ability to create anonymous classes on the fly, yet be able to pass them as a parameter to a method that is expecting an interface or subclass. In other words, I'd like to be able to do something like this:
public class MyBase { ... }
public void Foo(MyBase something)
{
...
}
...
var q = db.SomeTable.Select(t =>
new : MyBase // yeah, I know I can't do this...
{
t.Field1,
t.Field2,
});
foreach (var item in q)
Foo(item);
Is there any way to do this other than using a named class?
No. Anonymous types always implicitly derive from object, and never implement any interfaces.
From section 7.6.10.6 of the C# 5 specificiation:
An anonymous object initializer declares an anonymous type and returns an instance of that type. An anonymous type is a nameless class type that inherits directly from object.
So if you want a different base class or you want to implement an interface, you need a named type.
No. From the documentation:
Anonymous types are class types that derive directly from object, and that cannot be cast to any type except object.
To solve your problem, just replace the anonymous type with normal class...
Cannot extend an anonymous but you could declare your method to accept a dynamic parameter if you really need this to work.
Short answer: no
Long answer:
You could use a C# proxy class. There are several tools that can proxy classes. For example Moqs. https://github.com/moq/moq4
Related
I got the error for the below code
public static Moq.Mock<T> CreateInstanceOfIMock<T>() {
return new Moq.Mock<T>();
}
I have solved the error it by using referred class type. See this below code
public static Moq.Mock<T> CreateInstanceOfIMock<T>() where T : class
{
return new Moq.Mock<T>();
}
Now I want to move this var mockColorsRepository = new Moq.Mock<IColorsRepository>(); code into common code by using generics. here IColorsRepository is an interface. So I made an interface reference for T instead of class like this below code
public static Moq.Mock<T> CreateInstanceOfIMock<T>() where T : interface
{
return new Moq.Mock<T>();
}
But am getting The type T must be a reference type in order to use it as parameter error. How can I refer interface instead of class to T. How can I achieve this?
class and struct in generic type constaints do not mean the same thing as the class and struct declarations that are used to declare class or struct types. Instead, they only restrict whether a generic type argument is a reference type (class), or a value type (struct).
So when you do where T : class you are not saying that T needs to be a class, you are saying that T needs to be a reference type. Similarly struct for value types.
Interfaces on their own do not have this property, so an interface can be implemented by both a reference type and a value type. As such, restricting your type to be of an interface does not really make sense there.
In your case, Moq requires you to pass a reference type, so you need to transitively carry over that type constraint in all your helper methods:
public static Moq.Mock<T> CreateInstanceOfIMock<T>()
where T : class
{
return new Moq.Mock<T>();
}
That’s all you need to do to create a mock of any valid type. You can use it with an interface using CreateInstanceOfIMock<IColorsRepository>() or any other type.
Of course, at that point, the method does not really make that much sense since it does not give you any benefit over just instantiating the mock yourself.
There's no generic constraint in C# to enforce that a type argument is an interface. But where T : class is really "where T is a reference type" - it includes interfaces.
If you wanted to enforce that T is an interface rather than a class, you could perform an execution-time check using typeof(T) within the method, but in this case it sounds like you don't really need to constrain it to be an interface.
I'm not sure that the "helper" method is particularly useful though - if you compare:
var mock = Helper.CreateInstanceOfIMock<Foo>();
and
var mock = new Moq.Mock<Foo>();
or even (unless you have Mock<T> as another type somewhere) just a using Moq; directive and
var mock = new Mock<T>();
The latter seems just as readable and shorter... it makes sense if you're going to add more logic in your method, but if it's only ever going to call the constructor, I don't think I'd bother with it.
I know how you can use List<T> for example and decide what that collection is holding. That's where T comes in. But I'm not sure I understand the brackets fully.
If I create a class...
class MyClass<int> { }
Or instead of int I could use T or object or string or whatever. What does that mean? Does it turn into a collection automatically?
Generic classes allow class members to use type parameters. They are defined in the same way as generic methods, by adding a type parameter after the class name.
class Point<T>
{
public T x, y;
}
To instantiate an object from the generic class the standard notation is used, but with the type argument specified after both class names. Note that in contrast to generic methods, a generic class must always be instantiated with the type argument explicitly specified.
Point<short> p = new Point<short>();
Reference: http://www.pvtuts.com/csharp/csharp-generics
T means Type. MyClass is a generic class if you use "MyClass". More info here
I have two classes as below, one inherit from another. Nothing need to implement for this case.
Class super
{
//nothing
}
Class sub:super
{
//nothing
}
Now I create a instance as below statement
sub actualSub=new sub();
So, we have a instance actualSub. Which type object pointer is type sub and actual type is sub.
Consider their inherit relationship,Is there any way to convert actualSub's actual type to super?
In other words, how could I make actualSub.GetType() return type super?
Language is CSharp.
No it is not possible - GetType returns actual type of the object and there is no way to alter that behavior.
You can consider making copy if base class have some sort of copy constructor...
actualB.GetType().BaseType.Dump();
I need to clarify a thing that how an object type variables accept class type instance an given in the below code snippet,
class MyClass
{
}
static void Main()
{
object obj = new MyClass();
}
Since the MyClass is not a type of object but still the instance of MyClass is accepted in the obj(object) variable.
Actually, your class is an object.
In C# all classes derives from object.
Referring to a class as it's base type is one way of Polymorphism.
It might be better understood using an analogy:
Your class is an object, like a Dog is an animal.
Also, If you try the following:
object obj = new MyClass();
bool isMyType = obj == typeof(MyClass); //<--this will be true.
Take a look at this SO thread for more information how Polymorphism can be useful.
The concept that you do not understand is polymorphism which basically say that you can define an is relation between your classes. For a simple logic every dog is an animal so you can have class Dog that inherits from Animal. This implies that you can assign to variable of type Animal an instance of a Dog but not the other way around - not every animal is a dog. Another thing is that every thing derives form object this is language concept that you simply can take for granted.
Evrything in c# is derived from Object...
even your class.
.Net follows OOPs (Object Oriented Programming Language) and here every class can act as a object. Every class inherits Object class and hence every class can act as an object. In your example, .Net creates a default constructor to create instance of the class. You can definitely write your own constructor there.
Hope it helps.
Everything in C# is derived from Object.
Even Value Types like struct(int,float,..) are all derived from Object type.
When you define your own class,it implicitly derives from the Object type.
It is mentioned in the docs
All classes, structures, enumerations, and delegates inherit from
Object class
MSDN:
Supports all classes in the .NET Framework class hierarchy and provides low-level
services to derived classes. This is the ultimate base class of all classes
in the .NET Framework; it is the root of the type hierarchy.
Inheritance Hierarchy:
All classes, structures, enumerations, and delegates.
This means when you use int.Parse() to cast some value to int, there is a class behind int type which makes it able to have methods and do such stuffs. Object has been rooted pretty much everywhere in .Net.
I must do the following:
var someType = ObjectFactory.GetNamedInstance("myNamedInstance");
where someType can be any implementation of ICommand.
so I registered some of them:
For(typeof(ICommand<>)).Use(typeof(Command1)).Named("myNamedInstance1");
For(typeof(ICommand<>)).Use(typeof(Command2)).Named("myNamedInstance2");
is there a way to do this in StructureMap, because GetNamedInstance requires the type parameter which I don3t know until runtime.?
(For this, I'm assuming you created ICommand<T>)
This doesn't actually make any sense... think of the line:
//where aString is either myNamedInstance1 or myNamedInstance2
var someType = ObjectFactory.GetNamedInstance(aString);
Now assume that you are not going to use var, and instead the actual type. What would you put there that could compile? That is, what type can someType possibly be other than object?
Also, remember that ICommand<string> and ICommand<int> are both constructed types from ICommand<T>, but are not otherwise related - they have no common base type other than object.
If you don't the type until runtime, generics are not going to help a bunch - instead make your ICommand<T> inherit from some common interface - like ICommandBase - that has the methods you actually need.
However, if you just don't know the type in that method, you can push the unknown "up" in the compile by making the method containing that generic:
public void Execute<T>( string commandName)
{
var someType = ObjectFactory.GetNamedInstance<ICommand<T>>(commandName);
someType.Execute();
}
Now the caller of execute needs the type param... but again you could push that up. Notice that eventually you'll need the type parameter.