Add bindings for GtkStack and GtkStackSwitcher

[hugrs]

Hi,

I'm an OCaml beginner and I wanted to use the GtkStack widget from GTK 3.10+ in a small project.

I added bindings for GtkStack and GtkStackSwitcher, along with an example for the Stack widget. The bindings are very naive, I only added enough to make the examples compile with dune build @all.

Also I would like to ask for advice regarding some points:

The StackSwitcher has a "stack" property where you can get/set the GtkStack widget associated to it. As you can see in the stackswitcher.ml example, I am trying to use the set_stack method. However, it expects a Gtk.stack Gtk.obj and my variable is a GPack.stack. I don't know if I'm just missing an OCaml concept or that the type declarations in the binding are wrong, but I cannot figure out how to convert from one to the other.

My other concern is that GtkStack and StackSwitcher have only been introduced in 3.10, and I'm not sure how to handle backwards-compatibility with older versions. I have noticed the HASGTK* macros in C, should I do the same and define a HASGTK310 macro ?

[garrigue]

Thanks for your contribution. This looks fine. Concerning your two questions:

• If you need to extract the underlying widget from the ocaml object, you should add an as_stack method to the stack class. Look for instance at gWindow.ml for how to do that.
• For compatibility, the standard way is indeed to add macros. This said, at this point we do not do that in lablgtk3, and you would have to look at lablgtk2 for details. It also depends on whether there are enough old versions of gtk3 around to justify that. With lablgtk2 this was really a problem.

[hugrs]

Thank you for your quick reply. I added as_stack as a method in the stack class and it perfectly solved the type mismatch for stack_switcher. I completed the example as well so that both widgets have a working example.

Regarding the gtk3 version, I had a quick look in repology to see which versions of gtk are supported by mainstream distributions. Debian stable provides 3.24, and very few of them provide a version inferior to that. I think it's safe to assume that adding functionality from 3.22 and earlier without any extra checks should be fine. Let me know what you think.

[garrigue]

Actually, the README.md file states explicitly that lablgtk3 requires gtk+-3.18 or better. So GtkStack is already covered. We might raise the requirement in the future, rather than introducing conditional compilation.

Let me known when this is ready for inclusion.

[hugrs]

Ok then let's follow the requirements in the readme. There is just the icon-size property of stack_switcher that was added later in 3.20, so i've documented that. Now the PR is ready for review.