How to clear vim registers effectively?

Registers in vim are a great feature to store text snippets and even to run commands on the text stored within them. However, I'm a tidy person and tend to clean things up when I'm done.

I know that if I wanted to clear register a, I can use qaq.

I can also execute the following command:

:let @a = ''

However, these solutions seem like a mere workaround to the problem. When I execute :registers, the list still displays register a (with an empty value), while registers that have otherwise never been used are not displayed.

Is there a way to clear a register with the side-effect of removing the register from this list?

And if so, is there also a way to clear all registers at once, i.e., to reset that list of registers?

Since that venerable answer on the mailing list, linked by @romainl, we have setreg('a', []) that clears the register.

Thus, the code could become:

let regs=split('abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789/-"', '\zs')
for r in regs
  call setreg(r, [])
endfor

AFAIK you can't use built-in commands/functions to make registers disappear from the list. That seems to be doable only by removing them from your ~/.viminfo which sounds a bit extreme.

this thread on the vim mailing list has a command that clears every register but it doesn't remove them from :reg:

let regs='abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789/-"' | let i=0 | while (i<strlen(regs)) | exec 'let @'.regs[i].'=""' | let i=i+1 | endwhile | unlet regs

--- EDIT ---

The command above is no longer needed but here is a breakdown for the curious:

" The value of variable regs is a string made up of all named
" and numbered registers, plus the search, small delete, and
" unnamed registers. A string can be used as a list for our
" use case so we use the most concise method. We could have
" done let regs = ['a', 'b', 'c', etc. instead.
let regs = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789/-"'

" We are going to iterate through the string so we initialize
" a loop counter with value 0.
let i = 0

" Here is our loop where we check at each iteration if the loop
" counter is smaller than the length of regs.
while (i < strlen(regs))

    " If it is, we programmatically assign an empty string
    " to each corresponding register
    exec 'let @' . regs[i] . ' = ""'

    " and we add 1 to the loop counter.
    let i = i + 1
endwhile

" Once we are done, we get rid of the variable we created above
" which is now unnecessary.
unlet regs

Put this in your .vimrc:

command! WipeReg for i in range(34,122) | silent! call setreg(nr2char(i), []) | endfor

and clear every register with :WipeReg

If you would like that to happen every time you start Vim also add:

autocmd VimEnter * WipeReg

Remove .viminfo file or delete the register line in the .viminfo file.

You can get the details from Here:

The viminfo file is used to store:
- The command line history.
- The search string history.
- The input-line history.
- Contents of non-empty registers.
- Marks for several files.
- File marks, pointing to locations in files.
- Last search/substitute pattern (for 'n' and '&').
- The buffer list.
- Global variables

Another option is to never load any registers. As others have said, registers are loaded from .viminfo. The -i flag is used to specify what viminfo file to use. If you specify NONE, no viminfo, and therefore no registers will be loaded.

vim -i NONE

It is possible to set a value for each used register, similar to romainl's approach:

function! ClearRegisters()
   redir => l:register_out
   silent register
   redir end
   let l:register_list = split(l:register_out, '\n')
   call remove(l:register_list, 0) " remove header (-- Registers --)
   call map(l:register_list, "substitute(v:val, '^.\\(.\\).*', '\\1', '')")
   call filter(l:register_list, 'v:val !~ "[%#=.:]"') " skip readonly registers
   for elem in l:register_list
      execute 'let @'.elem.'= ""'
   endfor
endfunction

This avoids including additional register on the output of :registers

For the sake of completeness, I'll note that while setting a register to contain an empty string doesn't remove the register from the output of the :registers command, Vim does not save registers which have been cleared in this way to the .viminfo file.

Therefore, one other quick-and-dirty alternative for removing specific registers from the list is to clear them using either of the commands you suggest, and then restart Vim.