set aa bb cc -- dd ; f=$'\1' IFS=$f

recho "$f$*$f"
recho "$f--$f"

[[ $f$*$f == *$f--$f* ]] && echo ok 1
[[ $f$*$f == "$f--$f" ]] || echo ok 2

[[ ${f}${*}${f} == *$f--$f* ]] && echo ok 3

[[ $f$*$f == $f$*$f ]] && echo ok 4
[[ ${f}${*}${f} == $f$*$f ]] && echo ok 5
[[ $f$*$f == *--* ]] && echo ok 6

[[ $* == $* ]] && echo ok 7
[[ $* == ${*} ]] && echo ok 8
[[ $f == $f ]] && echo ok 9
[[ $f == ${f} ]] && echo ok 10

# now with f an array and $f -> ${f[0]}

set aa bb cc -- dd ; f=( $'\1' )

[[ $f$*$f == *$f--$f* ]] && echo ok 11
[[ ${f}${*}${f} == *$f--$f* ]] && echo ok 12
[[ $f$*$f == $f$*$f ]] && echo ok 13
[[ ${f}${*}${f} == $f$*$f ]] && echo ok 14
[[ $f$*$f == *--* ]] && echo ok 15

[[ $* == $* ]] && echo ok 16
[[ $* == ${*} ]] && echo ok 17
[[ $f == $f ]] && echo ok 18
[[ $f == ${f} ]] && echo ok 19

# now use an array instead of $*
A=( aa bb cc -- dd ); f=$'\1' IFS=$f

[[ $f${A[*]}$f == $f${A[*]}$f ]] && echo ok 20
[[ $f${A[*]}$f == *--* ]] && echo ok 21
[[ ${f}${A[*]}${f} == *$f--$f* ]] && echo ok 22

[[ ${f}${A[*]}${f} == $f${A[*]}$f ]] && echo ok 23
[[ ${A[*]} == ${A[*]} ]] && echo ok 24