#   This program is free software: you can redistribute it and/or modify
#   it under the terms of the GNU General Public License as published by
#   the Free Software Foundation, either version 3 of the License, or
#   (at your option) any later version.
#
#   This program is distributed in the hope that it will be useful,
#   but WITHOUT ANY WARRANTY; without even the implied warranty of
#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#   GNU General Public License for more details.
#
#   You should have received a copy of the GNU General Public License
#   along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
# this captures how bash and ksh93 expand indexed array subscripts in
# various contexts. if changes are ever made, or an option added to do
# this differently, the diffs will show up here

typeset -a array

index='$( echo >&2 foo )' # Literal shell code should never be evaluated unless an 'eval' is involved.

echo ${array[ $index ]} # [] expands $index, results in a literal that [] does not re-evaluate.
echo $(( $index )) # (( )) expands $index, results in a literal that (( )) does not re-evaluate.
echo $(( array[ $index ] )) # (( )) expands $index, results in a literal that  [] DOES re-evaluate.

(( array[ $index ] ))

typeset -a a

: $(( a[$index]=5 ))

#shopt -s assoc_expand_once
echo $((1+a[$index]))
echo $((1+a[\$index]))
echo "1+${a[$index]}"

# intermediate problems discovered while bash-5.0 was in testing
a=0
echo $(( a[a[0]] ))
echo ${a[a[a[0]]]}
echo $(( a[a[a[0]]] ))