Add support for dictionary types

[dsboger-zz]

I'm investigating the possibility of using ddbus to write a GNOME Shell search provider [1] for Terminix [2], but the interface for the search provider defines a method GetResultMetas whose return type signature is aa{sv}. I've scanned ddbus source code but could not find support for this data type. Are there any plans to support dictionary types?

[1] https://developer.gnome.org/SearchProvider/
[2] https://github.com/gnunn1/terminix

[trishume]

I made an attempt at adding support for serializing and deserializing associative arrays as dictionaries in this branch.

However the dbus service on my computer (OSX) is no longer working, so I can't actually test that my code works. All I can tell you is that it compiles on my version of D, if it doesn't compile for you try reverting the most recent commit on the branch which fixes a change in methods between versions.

If you test the code and tell me it works, or contribute any fixes necessary to get it to work, I'll merge it into master.

[WebFreak001]

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