Re: rfc: macros accepting constructors

[Andreas Schwab <schwab at suse dot de>]

Daniel Berlin <dberlin@dberlin.org> writes:

|> On Thu, 27 Jun 2002, Tim Hollebeek wrote:
|> 
|> > On Thu, Jun 27, 2002 at 10:02:32AM -0700, Aldy Hernandez wrote:
|> > > 
|> > > > Perhaps the best suggestion (if anything is desirable) is to modify
|> > > > grammar so that ()'s are allowed around any grammar element which is
|> > > > surrounded by {}'s.  Then all you have to do is remember to use ({ and
|> > > 
|> > > this already works.
|> > 
|> > I think you misunderstood.  The part of the grammar I was proposing to
|> > modify was the C grammar, not the preprocessor grammar.  What I suggested
|> > most definitely does NOT work right now:
|> > 
|> > d1.c: void foo(void) ({ int x, y; })
|> > d2.c: int x[2] = ({ 0, 0 });
|> > 
|> > d1.c:1: parse error before `{'
|> > d2.c:1: braced-group within expression allowed only inside a function
|> > 
|> > > but foo({1,2}) doesn't. 
|> > 
|> > What I'm proposing would allow foo({1,2}) to safely be rewritten as
|> > foo(({1,2})) regardless of how the { ends up getting used.
|> This conflicts with statement expressions (a gcc extension), probably 
|> irreconciably.
|> 
|> ({1,2}) is an almost valid statement expression with the value "2".
|> 
|> (It's invalid because you don't have a semicolon at the end of the 2)
|> 
|> Thus, foo(({1,2;})) would be equivalent to foo(2).
|> Try it, you'll get a "too many arguments" error if you have "void 
|> foo(void)", rather than some other weird error.

Going back to the OP's question, it was about this:

	#define foo(x) bar((x))

	foo((vector int){0, 1, 2, 3});

Since you can put parens around *every* valid expression, what is wrong
with writing this?

	foo(((vector int){0, 1, 2, 3}));

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
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