I'm not entirely sure what your actual goal is. I guess what you are trying to achieve seem to be better solved by
filterserves as validator in this case, i.e.,
people.filter(isFirstNameValid). This returns a collection of all people with a defined first name -- is this what you want?
mapserves as extractor of the desired field, in this case the first name. So overall
people.filter(isFirstNameValid).map(_.firstName)in case you want your collection to represent first names instead of a complete person. If you furthermore want to convert from
Option(of first name) to a concrete value you may want to use
flatMapinstead (this also makes the explicit validation unnecessary).
In case you really what to stick to a solution based on modifying external state, you have to place your mutable variable in an external scope for instance...
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