Is there a 'toggle' :set option?

Question

In my $VIMRC I have:

nnoremap <leader>A :set formatoptions+=a<cr>
nnoremap <leader>a :set formatoptions-=a<cr>

What I'm wondering is if there's something more like:

nnoremap <leader>A :set formatoptions!=a<cr>

that takes the value of a (the formatoptions flag) and inverts it (if set, unset it, otherwise set it).

This would be like

nnoremap <leader>s :set spell!<cr>

but for options where it takes flags rather than it being a true/false boolean. I'd like to accomplish this without getting into vimscript and if/else loops.

Answer 1

There is no built-in way to do this in vimscript that I'm aware of. You could put it in a function:

function ToggleOption(option)
  if &formatoptions =~# a:option
    exec "set formatoptions-=".a:option
  else
    exec "set formatoptions+=".a:option
  endif
endfunction

nnoremap <leader>A :<C-u>call ToggleOption('a')<cr>

But if you really want this as a one liner, you'd need something like this:

nnoremap <expr> <leader>a ":\<C-u>set fo".'+-'[&fo =~# 'a']."=a\<CR>"

In my opinion, this is kinda ugly and the function is much preferable.