Recently bought a couple of used books on C++/CLI to read. This looks like the most seamless and high performance approach to .NET/Native interop.

and

Both a little old (though there isn’t much newer really). I’m a bit concerned that Microsoft might move away from supporting this language as it must  be a bit involved to keep up as new releases happen. I’m going to look at adding some interop samples using this technology to my github in the near future.