Vim positive lookahead regex

If you check the vim help, there is not much to explain: (:h \@=)

\@=     Matches the preceding atom with zero width. {not in Vi}
        Like "(?=pattern)" in Perl.
        Example             matches
        foo\(bar\)\@=       "foo" in "foobar"
        foo\(bar\)\@=foo    nothing

This should match the last id:

/id\(_\d$\)\@=

save some back slashes with “very magic”:

/\vid(_\d$)@=

actually, it looks more straightforward to use vim’s \zs \ze:

id\ze_\d$