vim keep cursor position when counting matches - function

Question

I have a function to count and return the number of matches of some text:
function! count_matches()
redir => matches_cnt
silent! %s/\[\d*\]//gn
redir END
return split(matches_cnt)[0]
endfunction
I created a map to insert the return value of count_matches() at the current position:
noremap <C-A> Go[foo<C-R>=count_matches()<CR>]
However the cursor jumps to the beginning of the line after executing the silent %s/[\d*]//gn command. So when I press control+a vim inserts "[foo", then the function is being executed, the search command resets the cursor position and the return value is inserted at the beginning of the line resulting in "1][foo" instead of "[foo1]".
Can I somehow prevent count from changing the cursor position, or reset the cursor position after counting the matches?
The script also leads to an error, if the pattern is not found. How can I get the function to return 1 without an error for zero matches?

Answer 1

Even better then just to save the cursor position, is to save the complete viewport. (But that only works, if you do not change the window layout)
See :help winsaveview()
let wsv = winsaveview()
MoveTheCursorAround
call winrestview(wsv)
In your particular case, I would take another approach:
inoremap <expr> <f3> len(split(join(getline(1,'$'),"\n"), '\[\d\+\]',1))
Which takes the whole text, and splits it on the pattern \[\d\+\] and then counts how many elements there are. Or if you like to add some text:
inoremap <expr> <f3> '['.len(split(join(getline(1,'$'),"\n"), '\[\d\+\]',1)).']'
This will add the [ in front and ] after the number. Adjust the mapping key and text to your personal taste. (Note, you do not need the winsaveview() function, cause the cursor won't move).
It is perhaps not such a good idea to use that function on a multi MB text size. ;)

Answer 2

This is the same function, reworked to return 1 when there's no match:
function! count_matches()
redir => matches_cnt
try
silent! %s/\[\d*\]//gn
catch
echo 1
endtry
redir END
return split(matches_cnt)[0]
endfunction

Answer 3

See :help getpos()
let save_cursor = getpos(".")
MoveTheCursorAround
call setpos('.', save_cursor)

Answer 4

My solution:
function! CountWithCursorKeep(...)
let currentCursor = getcurpos()
let pattern = expand('<cword>')
if a:0 > 0 | let pattern = a:1 | endif
execute(':%s#' . pattern . '##gn')
call setpos('.', currentCursor)
endfunction
nmap ,ns :call CountWithCursorKeep(<C-R>/)<cr>
nmap ,nw :call CountWithCursorKeep(expand('<cword>'))<cr>
nmap ,nW :call CountWithCursorKeep(expand('<cWORD>'))<cr>
command! -nargs=? -bar -complete=tag CountMatch call CountWithCursorKeep(<f-args>)
You can use :CountMatch pattern to get how many times pattern occurs in current file.