I'm writing a C++ application and I want it to provide a generic UI
interface, which under the hood might be using GTK, Win32, etc. The goal is
that the app can be compiled with support for one or more UI backends and
the user can choose one at runtime, or at least that one backend can be
selected at compile time without changing the rest of the app.
So far I have a class UI with subclasses:
Class Widget (abstract base class)
Class Container: public Widget (abstract base for widgets which contain and
arrange other widgets)
Class Window: public Container (top-level window)
Class Display: public Widget (displays an image)
(I can't seem to get my phone to not write class with a capital there)
The app would use this something like:
UI::someSpecificBackend ui(argc, argv);
UI::Window win("some title");
UI::Display display();
win.add(display);
ui.add(win);
ui.run();
(Maybe not exactly like this, but roughly.)
Obviously this looks pretty similar to GTK, so I thought it should be
pretty simple to implement this backend:
Class GTK::UI: public UI, public Gtk::Application;
Class GTK::UI::Widget: public UI::Widget, public Gtk::Widget;
Class GTK::UI::Container: public UI::Container, public Gtk::Container;
Class GTK::UI::Window: public UI::Window, public Gtk::Window;
Class GTK::UI::Display: public UI::Display, public Gtk::Box;
The problem I run into is that the inheritance graph becomes a big mess and
the compiler can't make sense of it. GTK::UI::Window inherits Gtk::Widget
multiple times (through GTK::UI::Container, GTK::UI::Widget, Gtk::Window,
and Gtk::Container), leading to ambiguity, and it seems like virtual
inheritance doesn't help because some of those inheritance paths go through
a few layers in Gtkmm. (I can have Gtk::Window be virtual inherited by
GTK::UI::Window, but Gtk::Window and Gtk::Container both still
non-virtually inherit Gtk::Widget.) So I'm really not sure how to make this
work. Maybe I'm approaching it completely wrong?
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