Delphi Class of in C#

.net, c#, delphi, factory, oop

Solution

You can use Type:

Dictionary<ClassEnum, Type> TypeDictionary = new Dictionary<ClassEnum, Type>();

public void InitDictionary()
{
    TypeDictionary.Add(ClassEnum.FirstClass, typeof(FirstClass));
    //etc...
}

public object Factory(ClassEnum type)
{
    if (!TypeDictionary.ContainsKey(type))
        return null;

    var constructor = TypeDictionary[type].GetConstructor(....);
    return constructor.Invoke(....);
}

But I think you should use a generic method:

public T Factory<T>(): where T is MyBaseClass
{
    var type = typeof(T);
    var constructor = type.GetConstructor(....);
    return constructor.Invoke(....) as T;
}

Here is a variety for parameterized construction:

public T Factory<T>(params object[] args): where T is MyBaseClass
{
    var argList = new List<object>(args);
    var type = typeof(T);
    var argtypes = argList.Select(o => o.GetType()).ToArray();
    var constructor = type.GetConstructor(argtypes);
    return constructor.Invoke(args) as T;
}

And of course; As with the first example, this will throw a nullpointerexception if it can't find a matching constructor...

Problem

I know this question has been asked before, but I have yet to see a short, clear answer, so I'm hoping they won't remove this question and I will now get a clear answer: I am currently working in C# 5.0; .NET 4.5; VS 2012. I am mostly a Delphi guy although I've done lots with C#. In Delphi I have written hundreds of class factories that use the following sort of design (MUCH SIMPLIFIED HERE): ``` unit uFactory; interface type TClassofMyClass = class of TMyClass; TFactoryDict = TDictionary<TMyEnum, TClassofMyClass>; var fDict:TFactoryDict; implementation procedure initDict; begin fDict:=TFactoryDict.create; fDict.add(myEnum1, TMyClass1); fDict.add(myEnum2, TMyClass2); fDict.add(myEnum3, TMyClass3); end; function Factory(const aEnum: TMyEnum): TMyClass; var ClassofMyClass: TClassofMyClass; begin if fDict.TryGetValue(aEnum, ClassofMyClass) then result := ClassofMyClass.Create(aParam); end; end. ``` Now: HOW do I do something like this in C#?! Seems there is NO 'class of ' type in C#. Am I missing something? How can I implement this type of class factory simply and elegantly in C#? This design can be implemented in Python as well - why should C# be worse?!

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