Share configuration across `ftplugin` files without duplicating code

Question

A lot of languages use curly braces {} to enclose code blocks, so it's nice to have a mapping something like:

inoremap  <buffer>  {<CR>    {<CR>}<Esc>O

I have this mapping in my c.vim ftplugin, but also in: r.vim, scala.vim, and json.vim.

But this forces me to duplicate it four times. If I come up with an improvement, or I want to rebind the keys, I have to do it in each place.

Sourcing a shared script in each ftplugin seems like a good solution, but I'm not sure where the right place to put those shared scripts is. Putting them in plugin/ means they are loaded every time, which is not what I want. autoload/ seems to be designed for functions more than mappings, but perhaps there is a way to use it that way?

---

So, in short:

How can I define these mappings (but more generally, any part of an ftplugin) once, and then use them in multiple ftplugin files?

Answer 1

I see several ways to proceed

1. When I want to store code to load and execute on demand, I use the old macros/ directories.

   runtime macros/some_script.vim
   

2. Another approach is to put the mappings you which to define in a series of functions in an autoload plugin and to call the functions from the various ftplugins.

   call ns1#ns2#my_init_function1(args)
   

3. A third approach, which is the one I've chosen in lh-brackets in to have very generic mappings I use quite everywhere in a plugin/, and specialized <buffer>-mappings in buffers where I desire a different behaviour (in ftplugins). Of course, this works only when the specialized behaviour is not do nothing which is not standard.

PS: By experience, a mapping on {<cr> is a bad idea as it'll introduce a delay every time you'll type {. Having a contextual mapping on <cr> that detects whether there is a { before the cursor, or even if the cursor is between a pair of curly brackets, will give a much better user experience. See what I've done in lh-brackets.

if get(g:, 'cb_newline_within_empty_brackets', 1)
  " The following function will fall back to an existing previous
  " mapping definition, if any, or to default behaviour if the 
  " condition isn't met
  call lh#brackets#enrich_imap('<cr>',
        \ {'condition': 'getline(".")[col(".")-2:col(".")-1]=="{}"',
        \   'action': 'lh#brackets#_add_newline_between_brackets()'},
        \ 0
        \ )
endif