set -- "abc" "def ghi" "jkl"
A=("$@")

IFS=':'

echo 'IFS=: ${var-$*}'
unset var; printf '%s\n' ${var-$*}
printf '%s\n' ${var-${A[*]}}

echo "----"
echo 'IFS=: ${var=$*}'

unset  var; printf '%s\n' ${var=$*}
printf 'var=%s\n' "$var"

unset var; printf '%s\n' ${var=${A[*]}}
printf 'var=%s\n' "$var"

echo "----"
echo 'IFS=: ${var+$*}'

printf '%s\n' ${var+$*}
printf '%s\n' ${var+${A[*]}}

echo "----"
echo 'IFS= ${var-$*}'

IFS=''
unset var; printf '%s\n' ${var-$*}
unset var; printf '%s\n' ${var-${A[*]}}

echo "----"
echo 'IFS= ${var=$*}'

unset var
printf '%s\n' ${var=$*}
printf 'var=%s\n' "$var"

unset var
printf '%s\n' ${var=${A[*]}}
printf 'var=%s\n' "$var"

echo "----"
echo 'IFS= ${var+$*}'

printf '%s\n' ${var+$*}
printf '%s\n' ${var+${A[*]}}