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Back up Lists and Dictionaries to viminfo

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created October 6, 2012 · complexity basic · author Q335r49 · version 7.0

The "!" option in set viminfo stores string and number variables with all uppercase names to the viminfo file. A patch for vim 7.3 extends this behavior to lists and dictionaries, but apparently has problems with nested lists. This method doesn't have that limitation, and also has the advantage of working on earlier versions. It converts lists and dictionaries to a vimscript string, which then can be stored via the usual method in viminfo. The variables are recovered by executing that string.

By the way, this doesn't preserve the identity of lists. Variables that point to the same list will become copies of different but equivalent lists after restoring.

There are a few bits I had to look up:

  • Ctrl-A lists all possible completions. So you can get a list of all global variables via :let g:<c-a>.
  • For some reason directly writing a variable containing "\n" produces errors when sourcing the file, Vim treats it as an actual line break. We have to substitute the \n char with the string '."\n".'

Script

The following script can be placed in your vimrc.

fun! WriteVars()
    sil exe "norm! :let g:\<c-a>'\<c-b>\<right>\<right>\<right>\<right>v='\<cr>"
    let i=0
    for name in split(v)
        if name[2:]==#toupper(name[2:])	&& eval("type(".name.")")>1
            let g:VARSAV_{i}=substitute("let".name."=".eval("string(".name.")"),"\n",'''."\\n".''',"g")
            let i+=1
        en
    endfor
    "If the number of variables saved is less than last time, clear the extra ones
    if exists("g:VARSAVES") && i<g:VARSAVES
        exe "unlet! ".join(map(range(i,g:VARSAVES),"'g:VARSAV_'.v:val"))
    en
    let g:VARSAVES=i
endfun
fun! RestoreVars()
    if exists("g:VARSAVES")
        for i in range(g:VARSAVES)
            exe VARSAV_{i}
    endfor
en
au VimLeavePre * call WriteVars()

To restore the variables, use :call RestoreVars(). Note that if you use this in your vimrc file, you'll have to use :rviminfo to manually read the viminfo file first since the vimrc file is processed before the viminfo.

Comments

Does this script do anything not done by built-in Vim functionality, after version 7.3.30? --Fritzophrenic (talk) 04:49, October 7, 2012 (UTC)

I'm still running 7.3 compiled by someone long ago for android -- I don't have the means to compile a newer version. Also, the Windows version linked to from the vim.org website isn't patched. I haven't tested the patched version, the help file diff says "Nested List and Dict items may not be read back correctly, you end up with a string representation instead.". I'm not sure what they mean by "may", but this method does nested lists just fine.

It still doesn't do "pointers to the same list" of course, which probably can't be done in vimscript and would definitely require a patch. In my own vimrc file, I've added something along the lines of

if has_key(eval('dictname'),"reinitafterstorate")
  call add(list,"call ".dictname.".reinitafterstorage()")
end

into WriteVar(), so that the reinitafterstorage function would reinitialize any lists in the dictionary so that they point to the same address. I remember being really confused the first time this happened. --Q335r49 October 7, 2012

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