Cycle through autocomplete menu using tab

Question

I am activating my autocomplete menu in vim using:

inoremap <C-@> <C-n>

and after it opened and only when it opened I would like to use the "tab" key to cycle through the menu. But when it isn't open I would still like to use the "tab" key to write normal "tabs". Is this possible?

Thank you very much in advance.

Answer 1

Put the following insert-mode mapping (see :h mapmode-i) in your vimrc:

inoremap <expr> <TAB> pumvisible() ? "\<C-n>" : "\<TAB>"
inoremap <expr> <S-TAB> pumvisible() ? "\<C-p>" : "\<TAB>"

:h pumvisible() returns non-zero when popupmenu is visible and zero otherwise. :h :map-<expr> maps the key to the expression returned by the right hand side. And the whole expression is based on a ternary operator which ultimately states, map <Tab> to expression \<C-n> if popup-menu is visible and to expression \<Tab> otherwise.