(See the best response by Grind Knight.)
For example, if I wanted to combine c++ with DM and execute code written in c++ , is there a way I can do that? If so, how? It doesn't have to be in the exact same file. If I can just reference the function I need in another file that will be fine too.
Byondapi is now available. This is a set of structures and functions, that can be extended in the future, for greatly improved communication with native code in external libraries. call_ext() can call functions in the new format by prefacing their name with "byond:", which means no more having to convert everything to and from strings. Byondapi is capable of operations like reading and writing vars, calling procs, and more. An example project for your own external libraries is included in the BYOND distribution.

C:\Program Files (x86)\BYOND\byondapi\sample
Thank you, Grind Knight. And also thank you for your educative series on the DM, they're extremely helpful. Is there any sources that I can study regarding the BYOND API?
In response to Sefus
Best response
You're welcome! I'm glad you find the video series helpful!

The BYOND API is fairly new, so you'll have to ask around for other developers input. I haven't messed with it much myself yet. The example project found at
C:\Program Files (x86)\BYOND\byondapi\sample
Will hopefully be enough to get you started!