Case Study: Grep Operator, Part Three

Our shiny new "grep operator" is working great, but part of writing Vimscript is being considerate and making your users' lives easier. We can do two more things to make our operator play nicely in the Vim ecosystem.

Saving Registers

By yanking the text into the unnamed register we destroy anything that was previously in there. Further, by using a visual selection to yank the text in the case that our operator is applied with a motion, we also destroy any record of the most recent visual selection.

This isn't very nice to our users, so let's avoid using a visual selection in that case and also save the contents of the unnamed register before we yank in all cases so that we can restore it after we're done. Change the code to look like this:

nnoremap <leader>g :set operatorfunc=GrepOperator<cr>g@
vnoremap <leader>g :<c-u>call GrepOperator(visualmode())<cr>

function! GrepOperator(type)
    let saved_unnamed_register = @@

    if a:type ==# 'v'
        normal! `<v`>y
    elseif a:type ==# 'char'
        normal! `[y`]
    else
        return
    endif

    silent execute "grep! -R " . shellescape(@@) . " ."
    copen

    let @@ = saved_unnamed_register
endfunction

We've added two let statements at the top and bottom of the function. The first saves the contents of @@ into a variable and the second restores it. Additionally, we've applied yank with a motion rather than a visual selection in the case that our operator is applied with a motion.

Write and source the file. Make sure it works by yanking some text, then pressing <leader>giw to run our operator, then pressing p to paste the text you yanked before.

When writing Vim plugins you should always strive to save and restore any settings or registers your code modifies so you don't surprise and confuse your users.

Namespacing

Our script created a function named GrepOperator in the global namespace. This probably isn't a big deal, but when you're writing Vimscript it's far better to be safe than sorry.

We can avoid polluting the global namespace by tweaking a couple of lines in our code. Edit the file to look like this:

nnoremap <leader>g :set operatorfunc=<SID>GrepOperator<cr>g@
vnoremap <leader>g :<c-u>call <SID>GrepOperator(visualmode())<cr>

function! s:GrepOperator(type)
    let saved_unnamed_register = @@

    if a:type ==# 'v'
        normal! `<v`>y
    elseif a:type ==# 'char'
        normal! `[v`]y
    else
        return
    endif

    silent execute "grep! -R " . shellescape(@@) . " ."
    copen

    let @@ = saved_unnamed_register
endfunction

The first three lines of the script have changed. First, we modified the function name to start with s: which places it in the current script's namespace.

We also modified the mappings and prepended the GrepOperator function name with <SID> so they could find the function. If we hadn't done this they would have tried to find the function in the global namespace, which wouldn't have worked.

Congratulations, our grep-operator.vim script is not only extremely useful, but it's also a considerate Vimscript citizen!

Exercises

Read :help <SID>.

Treat yourself to a snack. You deserve it!

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