Bash: checking shell errexit shell option inside function, disabling it, and then restoring it.

foo.sh

#!/usr/bin/env bash

# Show how to check, save, restore the errexit shell option that is commonly set 
# using "set -e". This is useful for functions that care about non-zero exit statuses
# and want to do something because of it such as a retry function.

set -eu

echo "Shell options: $-"

function f(){
  local restore_errexit="";
  if [[ -o errexit ]] ; then
    restore_errexit="yes"
  fi;

  # Disable set -e because we rely on non-zero exit statuses for retrying
  # commands below.
  set +e
  echo "shell options with errexit disabled: $-"

  # whis command will fail
  which an_unknown_command
  
  # we wan
  if [ $? -ne 0 ] ; then
    echo "a failed command ran, yay!"
  fi

  # Re-enable set -e if it was previously turned on
  if [[ -n "$restore_errexit" ]] ; then
    set -e
  fi;
  echo "shell options with errexit restored': $-"
}

f;

echo "Shell options: $-"