How do I delete/unset a buffer local option (such as autoread)?

Question

In a new buffer, the expression &l:autoread evaluates to the value -1, indicating that the local option autoread has not yet been set with :setl autoread or :setl noautoread.

When I set the local option with :setl autoread, the expression evaluates to 1, when I unset it with :setl noautoread, it evaluates to 0. In either case, I won't be able to automatically have the global value for the option set with :set autoread.

So, is there a possibility to completely unset/delete the local option so that the expression &l:autoread will evaluate to -1 again?

Answer 1

You could directly set the local option to -1:

setl autoread
let &l:autoread=-1

At this point echo &l:autoread returns -1, and setl autoread? outputs --autoread, which is the exact same output of a new buffer, meaning that the global value is being used for that option:

                                                        *:setl* *:setlocal*
:setl[ocal] ...         Like ":set" but set only the value local to the
                        (...)
                        Without argument: Display local values for all local
                        options which are different from the default.
                        When displaying a specific local option, show the
                        local value.  For a global/local boolean option, when
                        the global value is being used, "--" is displayed
                        before the option name.

Answer 2

To remove a setlocal override option such that the global set is used instead, you can

:setlocal autoread<