I am going to code a text/code editor (GUI with QML and the rest in D*). But I have several problems:
I code the GUI with QML and C++ and then I connect it with a D-Backend for formatting etc. purposes. What is the best way to connect different Languages? Pipes, Sockets or in D the ability to use C++ Libraries?
IMHO rich text is used to format the text (in most cases). How is it possible to edit this "markup" in an easy way?? Is the formated code like a background image and the user edits an opaque non-formated-text?
Are there common techniques?
*Because QML is cool, platform indepedent and fast. On the other hand D is powerful and easy to use.
As you might know, there is QtD, Qt binding for D. It's not production ready right now, but it might be some day.
Another option would be connecting C++ and D, through C wrapper. This is the most commonly used way of interacting between C++ and D.
extern(C++) interfaces are specific to DigitalMars C++ compiler on Windows and are very limited, so that probably wouldn't help with your problem.
Also you might want to look at SWIG. It's a tool automatically generating glue code for interaction of other languages with C++. It supports D.
If performance is not an issue communications with D code could work through sockets or pipes.