libvterm | https : //github.com/neovim/neovim/wiki/Deps # forks

Although there are many mappings that will work (any 32-bit structure with the right methods used to fetch the values), the canonical way to map this directly is by using JNA's Union class. The Union will have three elements; either a byte, or a structure RGB that you can define (an inner class of the Union is fine), or a structure Indexed that you will define (again, an inner class).

The Union will allocate enough memory on the native side for the largest element (32-bits), and given the structure options you're guaranteed that the first 8 bits of the resulting 32-bit C-side memory will contain the type field; based on that value you'll know what is contained in the remaining 24 bits.

If you look at the source code of JNA's Variant class which maps the tagged union VARIANT, you'll see this implemented on a slightly more complex scale. The _VARIANT class contains these five elements, similar to the 3 elements in your union: