bash destructuring assignment for arrays

destruct-alternatives.sh

#!/bin/bash
## Alternative Versions

# only allows space separated variable name list
# example: destruct a b c = arr
destruct() {
  for ((i=1;i < $#-1; ++i)) do
    local value_adress="${!#}[$i-1]"
    declare -g "${!i}=${!value_adress}"
  done
}

# only allows comma separated variable name list
# example: destruct a,b,c = arr
destruct() {
  local var_names=(${1//,/ })
  for ((i=0; i < ${#var_names[@]}; i++)) do 
    local value_adress="$3[$i]"
    declare -g "${var_names[$i]}=${!value_adress}"
  done
}


# only allows compact form
# example: destruct a,b,c=arr
destruct() {
  local var_names="${1%%=*}"
  var_names=(${var_names//,/ })
  for ((i=0; i < ${#var_names[@]}; i++)) do 
    local value_adress="${1#*=}[$i]"
    declare -g "${var_names[$i]}=${!value_adress}"
  done
}

destruct.sh

#!/bin/bash
# destructuring assignment allows you to extract individual items from
# an array and place them into variables using a shorthand syntax
#
# allows mixed comma and space separated variable name list
#
# note:
#   do not use consecutive commas do not skip over values!
#   good: destruct a, _, c = arr
#   bad:  destruct a,,c = arr
#
# the following behave equally:
#   destruct a b c  d = arr
#   destruct a, b, c, d = arr
#   destruct a,,b  c, d = arr
#
# example:
#   connection_config=(127.0.0.1 3306)
#   destruct host, port = connection_config
#
# if more variable names are specified than the array is long,
# remaining variables will be set to an empty string
#
# author: jtbrinkmann

## short form
destruct() {
  local variable_names=${@:1:$#-2}
  variable_names=(${variable_names//,/ })
  for ((i=0; i < ${#variable_names[@]}; i++)) do 
    local value_name="${!#}[$i]"
    declare -g "${var_names[$i]}=${!value_name}"
  done
}

## documented code
# adhering to the Google styleguide for shell scripts
# https://google.github.io/styleguide/shellguide.html

#######################################
# destructuring assignment for arrays
# Arguments:
#   variable names to assign to (mixed comma/space separated or mixed)
#   equal sign
#   array variable name
# Outputs:
#   if 2nd to last argument isn't an equal sign,
#   an error message is written and the function will stop
#######################################
destruct() {
  local equal_sign_parameter="${@:$#-1:1}"
  local array_name="${!#}"

  if [ "=" != "$equal_sign_parameter" ]; then
    echo "incorrect usage" >&2
    echo "usage: destruct [variable_name]... = array_variable_name" >&2
    echo "" >&2
    echo "example:  destruct a b c = sample_array" >&2
    echo "example:  destruct a,b,c = sample_array" >&2
    echo "example:  destruct a, b, c = sample_array" >&2
    false
  else
    # get all variable names (every parameter except the last 2)
    local variable_names=${@:1:$#-2}

    # split comma separated names
    variable_names=(${variable_names//,/ })

    for ((i=0; i < ${#variable_names[@]}; i++)) do 
      # to get the array's value at the current index, we must first
      # build a string with the array variable's name and the index 
      local value_adress="$array_name[$i]"

      # and then resolve it
      local value="${!value_adress}"

      # and set the variable to that value
      local variable_name="${variable_names[$i]}"
      declare -g "$variable_name=$value"
    done
  fi
}