I used to use Gtkmm, but I realized something that should have been obvious in the first place. You can still use Gtk+ with C++, which is what I do. The only catch is that signals have to be friends if you want them to have access to private data members.
The only advantage of Gtkmm is that if gives you the same style of programming as c++ by using classes and namespaces that are wrappers of Gtk+. But, it not only doubled my executable size, but also required my users to install extra libraries. Also, Debian is always behind with the Gtkmm packages, so don't expect to have the most current, or even recently released Gtk+ versions at your disposal through the wrapper without requiring your users to compile Gtkmm directly from the sources.
Wrappers are great for some things, but not for most. And about the wrapper for GtkSourceView, it doesn't exist. There are some amateur projects for it that wrap some of the basic functions, but when I used it, I had to write my own wrapper for it. But then again, you can still use GtkSourceView with Gtkmm by using the Glib::wrap function provided. It will convert it from a GtkWidget* to a Gtk::Widget*.
Disclaimer: Just as a note, I don't mean to insult anyone with my bashing of Gtkmm. It really is a great set of libraries and has its uses. It is just not for me & I wanted to help people to learn from my mistakes so they can make an informed decision. :)
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