vim function to replace selection with current register

gistfile1.vim

function! ReplaceWithRegister(type, ...)
  let sel_save = &selection
  let &selection = "inclusive"
  let reg_a = @a
  let reg_z = @z
  let @z = @@

  if a:0  " Invoked from Visual mode, use '< and '> marks.
    silent exe 'normal! `<' . a:type . '`>"ad"zP'
  elseif a:type == 'line'
    silent exe "normal! '[V']\"ad\"zP"
  elseif a:type == 'block'
    silent exe "normal! `[\<C-V>`]\"ad`[\"zP"
  else
    silent exe 'normal! `["ad`]"Ax"zP'
  endif

  let &selection = sel_save
  let @@ = @a
  let @a = reg_a
  let @z = reg_z
endfunction

" map to ;
" typing ;w replace a word with current register
nmap <silent> ; :set opfunc=ReplaceWithRegister<CR>g@
vmap <silent> ; :<C-U>call ReplaceWithRegister(visualmode(), 1)<CR>