Show relative number column when using certain operator keys

relativenumber_op.vim

" Requires 'timeoutlen' to be low enough for this to be practical:  
" set timeoutlen=100

function! s:relative_number_op(key) abort
  let old_rn = &l:relativenumber
  let &l:relativenumber = 1
  redraw

  let seq = a:key
  while 1
    echo seq
    let next_key = nr2char(getchar())
    if next_key ==# "\<esc>"
      let seq = next_key
      break
    endif

    let seq .= next_key

    if next_key !~# '\d\+'
      break
    endif
  endwhile

  let &l:relativenumber = old_rn
  redraw

  return seq
endfunction


function! s:op_hook(key) abort
  execute 'nnoremap <silent><expr> ' . a:key . ' <sid>relative_number_op("' . a:key . '")'
endfunction


call s:op_hook('c')
call s:op_hook('d')
call s:op_hook('y')