@aeva If I was going to move away from C++, my next choice would be D. I haven't played with its concurrency stuff yet, but almost everything else I've done in it I liked. Garbage collection, but its optional. C and C++ interfacing. Inline assembler. Compile time function evaluation. Looks mostly like C++.
It's the only language I've found that can match the features of my freaky C++
vector maths library (and do it easier). :)