www.digitalmars.com         C & C++   DMDScript  

digitalmars.D - Abstract static methods

Hi all. I'm new to D and this is my first time posting here so please forgive me
if this topic has been covered before. I looked this up in the D spec at the
DigitalMars website and as far as I can tell it is not a feature of D so I
thought I'd post my thoughts about it in the hopes that perhaps a future version
of D can include it. I'm also very curious to read other programmers' opinions
on the usefulness of this language feature and whether or not the same effect
can be achieved in existing languages such as C/C++/C#, or D. So without further

I'm writing a UI library in C++ and want the various components/control TYPES to
register themselves as part of a component set. Note that I want their types
registered, not individual instances.

So, to make registration a class-level operation I use a static method:

class Component
static bool RegisterType(ComponentSet* compSet);
static Component* Create();

The body should look something like this for each derived component:

// class Button: public Component
bool Button::RegisterType(ComponentSet* compSet)
compSet->Register("Button", &Create);

Button* Button::Create()
return new Button();

// class TextBox: public Component
bool TextBox::RegisterType(ComponentSet* compSet)
compSet->Register("TextBox", &Create);

TextBox* TextBox::Create()
return new TextBox();

As you can see I want each class derived from Component to provide their own
implementations of the static methods RegisterType and Create. The problem is
that in C++ there is no way to FORCE programmers who derive from Component to
re-write Component's static methods. That means that someone could derive a new
component and forget to provide some vital functionality.

What I would love to see in a language is a way to have a sort of "abstract
static" method. Using C++ syntax it would look like this:

class Component
static bool RegisterType(ComponentSet* compSet) = 0;
static Component Create() = 0;

The compiler would then require any derived classes to implement their own
versions of the static methods.

Apr 27 2004