Completion and aliases - how to alter command line?

["Alexey I. Froloff" <raorn@xxxxxxxxxxxx>]

I have function _foo that completes arguments for command foo.  I
have alias bar='foo --baz=quux'.  How do I enable completion of
command bar like foo and have --bar option available to _foo?
Doing

$ compdef _foo bar

will not do what I want.

-- 
Regards,
Sir Raorn.

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