How to cmap a local function?

Question

I'd like to reproduce this zsh mapping:

smart_dot() {
  if [[ $LBUFFER = *.. ]]; then
    LBUFFER+=/..
  else
    LBUFFER+=.
  fi
}
zle -N smart_dot
bindkey -M viins -- . smart_dot

At first I used this:

function! Smart_dot() abort
  if getcmdtype() =~# '[:]'
    let l:cmd=getcmdline()
    if match(l:cmd, '\.\.$') !=-1
      return '/..'
    else
      return "."
    endif
  else
    return getcmdline()
  endif
endfunction
cnoremap . <c-r>=Smart_dot()<CR>

but how do turn this into local function? I've tried many variants on this that wouldn't work because it complained <SID> was not used in a script context. Do I need to use <c-r>= or <c-\>e? Do I need to use the expand(<sfile>) trick to get the script number, described near the end of section :h script-local? Or do I need to <Plug> this? I'm confused.

" function! s:smart_dot() ...
cnoremap . <C-\>ecall(function('<SID>smart_dot()'), [])<CR>

Answer 1

You may use <sid> directly in this context like any other key code:

cnoremap . <c-r>=<sid>Smart_dot()<cr>

The reason is the *map family of commands are special in that they convert key codes to actual real characters. For example, <cr> is converted to a carriage return, code 13, and <c-r> is converted to code 18.