https://crates.io/crates/cxx is the simplest way to do an integration. It is slightly more work than "just plop in" but it's not incredibly difficult. It's harder than mixing C and C++ together, but then again, almost no pairings of languages are that easy.
Rust people keep saying there are not classes, but all a class needs it the ability to put methods on structs. Private access to some of the internals is often useful, but doesn't need to be enforced by the compiler.
You can also have implement different associated functions based on properties of generic arguments, which is quite different in design from just attaching methods to a struct.
Also, while not in C++, in many languages, classes imply heap allocation, where structs do not.
The different allocation between structs and class objects in C# is a total head scratcher. Didn't it ever occur to the language designers that someone might want to choose how to allocate memory?
https://www.fluentcpp.com/2017/06/13/the-real-difference-bet...
Maybe it was the era that I learned C++ (which was in the 98 days), but I was taught something closer to this convention, and didn't realize until just now there was such little difference by the book. Just bundling some data together? Use a struct. Doing more? Use a class.
I still think this distinction is useful overall, because there often is more of one in many languages, but I will be more precise when speaking about C++ specifically in the future. I would also still argue the same thing overall, that is, Rust does not have what C++ calls classes. Our structs are apparently even simpler than C++ structs.