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From: karl@haddock
Newsgroups: net.lang.c
Subject: Re: Orphaned Response
Message-ID: <86900055@haddock>
Date: Tue, 16-Sep-86 19:20:00 EDT
Article-I.D.: haddock.86900055
Posted: Tue Sep 16 19:20:00 1986
Date-Received: Sat, 27-Sep-86 13:34:20 EDT
References: <559@hadron.UUCP>
Lines: 27
Nf-ID: #R:hadron.UUCP:559:haddock:86900055:000:1427
Nf-From: haddock!karl    Sep 16 19:20:00 1986


hadron!jsdy (Joe Yao) writes:
>In article <1761@mmintl.UUCP> franka@mmintl.UUCP (Frank Adams) writes:
>>[haddock!karl (Karl Heuer) writes:]
>>>For another, the types might be
>>>unknown, if they are arguments in a macro; in this case I would want the
>>>macro to work on void as well as valued expressions.
>>This case is not covered by my suggestion.  I find it hard to imagine doing
>>it, however.
>When would one try to pass a void "value" to anything, whether or
>not it is a macro?  (I agree, that is  v e r y  hard to imagine!)

Your comment "whether or not it is a macro" suggests that you are assuming
the macro has function semantics, in which case it would not be useful to
hand it a void expression.  But not all macros have this property; consider
    #define new(T) ((T *)malloc(sizeof(T)))
which expects a type rather than an expression.

What I was thinking of (I don't have a specific instance) was a macro whose
return value has the same type as its arguments -- like generic MIN and MAX.
To concoct something that would accept void arguments, you could write
    #define foo(e1,e2) (SOMETHING ? (SOMETHING,(e1)) : (SOMETHING,(e2)))
I suppose.  Of course, the user must be aware that this is a macro, and that
its value is void when its arguments are.  In any case, I agree that it's
not all that likely, but it's not inconceivable.

Karl W. Z. Heuer (ima!haddock!karl; karl@haddock.isc.com), The Walking Lint