an class='id identifier rubyid_return_value'>return_value</span> <span class='op'>=</span> <span class='id identifier rubyid_block'>block</span><span class='period'>.</span><span class='id identifier rubyid_call'>call</span>
  <span class='comment'># Restore previous value
</span>  <span class='id identifier rubyid_keys_to_overwrite'>keys_to_overwrite</span><span class='period'>.</span><span class='id identifier rubyid_each_key'>each_key</span> <span class='kw'>do</span> <span class='op'>|</span><span class