Print associative array keys on separate lines in Bash?

Question

Similar to this Print array elements on separate lines in Bash? but printing only the keys.

The answer on that other one %s\n' "${myarray[@]}" when used on an associative array prints the values only while I'm looking for the keys.

declare -r -A myarray=(
   [a]=1
   [b]=2
   [c]=3
   [d]=4
)

Would like to have:

a
b
c
d

Answer 1

So just:

printf "%s\n" "${!myarray[@]}"