Question:
Are there power bit set classes around that can do what Verilog, VHDL can do so easily?

a[3:2,0] = b[4:1] & c[5]; // collections of width n mixed with 1

Doing this bit by bit (wire by wire), follows the textbook but is also slow. I could “” everything and interpret, or write a full blown compiler for a tiny lang, but using C++/classes is much more expresive.
Any suggestions?

Answer:
Yes, there are bit-oriented classes in the Standard Library, namely std::bitset and the specialization std::vector, which manipulates bits.
Both of these classes offer a high level interface for bit manipulation. You can find more information about their usage in any decent STL book.