how to pass an Action<in T> with a derived class as the Action parameter?

Question

Given:

class BaseClass {}
class DerivedClass : BaseClass {}

I want to write a function that can accept an Action with a BaseClass parameter. The function will create an object of the specified type and pass it to the Action.

void MyFunction(Type type, Action<BaseClass> DoAction)
{
  BaseClass obj = (BaseClass)Activator.CreateInstance(type); 
  DoAction(obj);
}

I want to pass in AnotherFunction whose parameter is a DerivedClass:

void AnotherFunction(DerivedClass x)
{
}

How should I call MyFunction? The following is invalid due to the AnotherFunction argument:

MyFunction(typeof(DerivedClass), AnotherFunction);

Answer 1

If at all possible, try to use generics instead:

void MyFunction<T>(Action<T> DoAction) where T : BaseClass, new()
{
    DoAction(new T());
}

Then you can just write:

MyFunction<DerivedClass>(AnotherFunction);

This will:

• Do compile time checking to ensure the type you use is BaseClass or a type deriving from it. You won't get runtime errors because the type doesn't extend BaseClass.
• Do compile time checking to ensure that the type has a parameterless constructor, rather than throwing an exception at runtime if one doesn't exist.
• Do compile time checking to ensure that the method provided for the Action accepts a parameter appropriate for the type used, instead of throwing an exception at runtime if the type isn't appropriate.