After recently starting to port KDiff3 to KDE Frameworks 5, I made a few commits today making the software actually usable.
Commit 468652ce70b1214842c passes command line arguments, most importantly filenames of files to diff and merge, to the inner classes which do the actual work. The old code uses KDE 4's KCmdLineArgs which provided static functions to retrieve command line arguments from anywhere in the code. The new code processes command line arguments using QCommandLineParser in the main function and then passes this object down into inner classes. This makes the code working although it may not be the best design (I may consider a refactoring in the future).