How can I define an operator that takes a register as an argument?

Question

I'm trying to write a "Paste-over" operator. It will work like a combination of p and R, so it will paste the contents of a register over the text currently in the buffer. I have this so far:

function! PasteOver(before)
  if a:before
    call feedkeys("m`")
  endif

  call feedkeys("R")
  for i in split(@", '\zs')
    call feedkeys(i)
  endfor
  call feedkeys("\<esc>")

  if a:before
    call feedkeys("\<C-o>")
  endif
endfunction

nnoremap <M-p> :<C-u>call PasteOver(0)<cr>
nnoremap <M-P> :<C-u>call PasteOver(1)<cr

And it works great. However, I have a dilemma. I'd like this operator to work with registers, the same way that p does, e.g. "a<M-p> will paste over from the contents of register 'a', and have this work with every register.

There's two ways I could think of to do this:

• Write a mapping for every single register. I think it goes without saying that this is a terribly inefficient and sloppy way of doing this.

• Make the register argument come after the operator, so "a<M-p> would become <M-p>a. This would work fine, but it makes pasting from the default register less convenient, and I prefer the first way since it feels more natural (since my fingers have already learned "ap

Is there a builtin way to get the register argument to an operator? I'm thinking something like v:count, but v:register instead.

Answer 1

You can use v:register to grab the name of the last register supplied to a command, getreg() to grab its contents, and <c-r>= to insert text from a register when in insert (or replace) mode:

nnoremap <m-p> R<c-r>=getreg(v:register)<cr><esc>
nnoremap <m-P> R<c-r>=getreg(v:register)<cr><esc>`[

You can also use `[ to jump to the beginning of the last changed text.