I agree, the copies are ugly. I expect them to be optimized away by the compiler tough (I haven't checked, it should be an interesting thing to do).
Named and default arguments just postpone the problem. If you have many optional fields your code will likely include a lot of if Some(val)... to handle them.
These ifs will be a runtime penalty - unless the compiler can again optimize away. Using types you can achieve static dispatch and incur in no runtime penalty (at expense at slower compilation and bigger code size).
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