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Letting variable values be overwritten in a script

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Tip 82 Printable Monobook Previous Next

created 2001 · complexity basic · author Salman Halim · version 6.0


This is a simple function I wrote to get the value of a variable from three different places (in that order): the current buffer, the global setting or from the script itself.

This allows me to set a default value for a configuration variable inside my script and the user to change it on a global level by setting the same variable with a g: prepended. then, they can further set it on a per-buffer level by the b: mechanism. One of the examples for this might be my comments script (not uploaded). I have a variable in there that determines whether comment characters (// for java, for example) are placed the beginning of the line or just before the first-non-blanks in the text. I set up a default in my script:

let g:comments_hug_start_of_line=0 " comments should hug the text

that's fine as a default, but if I want to overwrite it for Vim scripts, I just put the following in my ftplugin/vim.vim:

let b:comments_hug_start_of_line=1 " Vim comments should hug the first column, always

" Tries to return the buffer-specific value of a variable; if not
" found, tries to return the global value -- if that's not found
" either, returns an optional default value or -1 if not specified.
function! GetVar(...)
  let varName=a:1
  if (exists("a:2"))
    let retVal=a:2
  else
    let retVal=-1
  endif
  if (exists ("b:" . varName))
    exe "let retVal=b:" . varName
  elseif (exists ("g:" . varName))
    exe "let retVal=g:" . varName
  endif
  return retVal
endfunction

So, to specify the default scope for java bean properties (used inside javabean.vim, though I chose not to put this mechanism in there to avoid the dependency on this function), I just use:

let current_javabean_scope = GetVar("javabean_scope", "protected")

If there is a buffer or global variable set, it uses that; otherwise, it defaults to protected scope.

CommentsEdit

I have a similar function in a library-plugin (implemented as an autoload plugin) for Vim 7. The difference is that I always force the script author to specify the default value as we can never know (as a library writer) if the option is a string or a number -- thus the best way to have an unique access point in script functions is to define an accessor:

let s:defaultMyFooOption = "bar"
function s:MyFooOption()
   return lh#option#Get("myFooOption", s:defaultMyFooOption)
endfunction

This way, it is possible to specify the default value as a script variable, and still define the generic function in a VimL library.

BTW, the function I use is the following:

" {rtp}/autoload/lh/option.vim
"
" Function: lh#option#Get(name, default [, scope])            {{{2
" @return b:{name} if it exists, of g:{name} if it exists, or {default}
" otherwise
" The order of the variables checked can be specified through the optional
" argument {scope}
function! lh#option#Get(name,default,...)
  let scope = (a:0 == 1) ? a:1 : 'bg'
  let name = a:name
  let i = 0
  while i != strlen(scope)
    if exists(scope[i].':'.name) && (0 != strlen({scope[i]}:{name}))
      return {scope[i]}:{name}
    endif
    let i += 1
  endwhile
  return a:default
endfunction

NB: it can also support window-variables (w:), tab-variables (t:), arguments (a:), ... See :help internal-variables

--Luc Hermitte 13:09, 30 July 2007 (UTC)


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