The way I ended up structuring my opcodes was similar to your way but a little different still. I ended up using function pointers but an array of them. Each opcode is defined in an enum and will be assigned to each funtion pointer based on it's corresponding array index. When the virtual CPU reads an opcode it just calls the function pointed to by the pointer at that index.

I found doing it this way makes it easy to change or add opcodes without needing to go back through a giant switch statement to find and rearrange everything. As a bonus too, the assembler just uses the same enum and basically just works through it the opposite way the CPU does. Translating keywords to the matching opcode index in the array then writing the index to the correct memory address in the binary. This also means any time I update an opcode or add one in the virtual machine all I have to do is add it to the enum and both the assembler and virtual machine will be updated without having to do anything else.