function init_param {
  typeset _a="$1$2$3" _p _q
  _p="${_a%%=*}"
  eval "$_p=; unset $_p"
  [[ "$_a" = "$_p" ]] || eval $_p=\"${_a#*=}\"
}

# init_param a=b
# init_param a =b
# init_param a= b
# init_param a = b
# init_param a = " b c  "