A shim for Bash's mapfile to support mapping key value pairs into an associative array

mapfile_assoc_shim.sh

#!/usr/bin/env bash
# mapfile_assoc_shim.sh
# If mapfile does not have a -A associative array mode
# then implement it
# Usage:
# include mapfile_assoc_shim.sh
# or
# . mapfile_assoc_shim.bash
#
# Example:
# IFS='=' mapfile -A assoc_array <<<$'key1=value1\nkey2=value2'
# 
if ! { mapfile -A _ </dev/null; } 2>/dev/null; then
  mapfile() {
    local k v d
    local -n A=${*: -1:1}
    declare -gA "${!A}"
    if [ "${*: -2:1}" = -A ]; then
      if [ "${*:1:1}" = -d ]; then
        d=${*:2:1}
      else
        d=$'\n'
      fi
      while read -rd "$d" k v || [ "$k" ]; do
        # shellcheck disable=SC2034 # nameref use
        [ "$k" ] && A[$k]=$v
      done
    else
      command mapfile "$@"
    fi
  }
fi