One way to solve this problem is to leverage generics and the new() constraint.
Instead of expressing your constructor as a method/function, you can express it as a factory class/interface. If you specify the new() generic constraint on every call site that needs to create an object of your class, you will be able to pass constructor arguments accordingly.
For your IDrawable example:
public interface IDrawable
{
void Update();
void Draw();
}
public interface IDrawableConstructor<T> where T : IDrawable
{
T Construct(GraphicsDeviceManager manager);
}
public class Triangle : IDrawable
{
public GraphicsDeviceManager Manager { get; set; }
public void Draw() { ... }
public void Update() { ... }
public Triangle(GraphicsDeviceManager manager)
{
Manager = manager;
}
}
public TriangleConstructor : IDrawableConstructor<Triangle>
{
public Triangle Construct(GraphicsDeviceManager manager)
{
return new Triangle(manager);
}
}
Now when you use it:
public void SomeMethod<TBuilder>(GraphicsDeviceManager manager)
where TBuilder: IDrawableConstructor<Triangle>, new()
{
// If we need to create a triangle
Triangle triangle = new TBuilder().Construct(manager);
// Do whatever with triangle
}
You can even concentrate all creation methods in a single class using explicit interface implementation:
public DrawableConstructor : IDrawableConstructor<Triangle>,
IDrawableConstructor<Square>,
IDrawableConstructor<Circle>
{
Triangle IDrawableConstructor<Triangle>.Construct(GraphicsDeviceManager manager)
{
return new Triangle(manager);
}
Square IDrawableConstructor<Square>.Construct(GraphicsDeviceManager manager)
{
return new Square(manager);
}
Circle IDrawableConstructor<Circle>.Construct(GraphicsDeviceManager manager)
{
return new Circle(manager);
}
}
To use it:
public void SomeMethod<TBuilder, TShape>(GraphicsDeviceManager manager)
where TBuilder: IDrawableConstructor<TShape>, new()
{
// If we need to create an arbitrary shape
TShape shape = new TBuilder().Construct(manager);
// Do whatever with the shape
}
Another way is by using lambda expressions as initializers. At some point early in the call hierarchy, you will know which objects you will need to instantiate (i.e. when you are creating or getting a reference to your GraphicsDeviceManager object). As soon as you have it, pass the lambda
() => new Triangle(manager)
to subsequent methods so they will know how to create a Triangle from then on. If you can't determine all possible methods that you will need, you can always create a dictionary of types that implement IDrawable using reflection and register the lambda expression shown above in a dictionary that you can either store in a shared location or pass along to further function calls.
