How can I join elements of an array in Bash?

 #!/bin/bash

foo=('foo bar' 'foo baz' 'bar baz')
bar=$(printf ",%s" "${foo[@]}")
bar=${bar:1}

echo $bar

from: https://stackoverflow.com/questions/1527049/how-can-i-join-elements-of-an-array-in-bash/53050617