R: extract names of partially named vector

Question

I have a vector that is partially named. All values (and names) are distinct.

my_vec <- c('one',
           'two' = '2',
           'three' = '3')

Sometimes I need the values i.e. unique(my_vec) which returns c("one","2","3"). I now need the "opposite" that is: c("one","two", "three"). Note that names is insufficient because the vector is partially named.

Is there a base R or tidy way to return the names of vector elements where available and vector values otherwise?

Apologies, this feels like something that should have an easily accessible answer on here but I can't find it anywhere.