Vim function to perform easy retabs ( eg. change file with softtabstop=4 to softtabstop=2 )

ReTab.vim

function! ReTab( tabsize )
  " Description: Change indentation when tab size is changed
  " Primarily used to convert an indentation of eg. 4 to 2 or vice-versa
  if &expandtab
    let l:tabstop_old     = &tabstop
    let l:softtabstop_old = &softtabstop
    let l:shiftwidth_old  = &shiftwidth

    let &tabstop = &softtabstop
    set noexpandtab
    retab!
    let &tabstop = a:tabsize
    set expandtab
    retab!

    let &tabstop = l:tabstop_old
    let &softtabstop = a:tabsize
    if (l:shiftwidth_old == l:softtabstop_old)
      let &shiftwidth = a:tabsize
    endif

  else
    let &tabstop = a:tabsize
  endif
endfunction
command! -nargs=1 ReTab call ReTab(<args>)