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From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <2467bc3b-c0da-b6e4-1201-48983ba5a5af@redhat.com>
Date: Wed, 21 Mar 2018 15:49:13 +0100
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Subject: Re: [Qemu-devel] [PATCH 2/3] qobject: assume base of a qobject is
 at offset 0
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To: =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= <marcandre.lureau@redhat.com>, Eric Blake <eblake@redhat.com>
Cc: qemu-devel <qemu-devel@nongnu.org>, "P. Berrange, Daniel" <berrange@redhat.com>, "Armbruster, Markus" <armbru@redhat.com>

On 21/03/2018 15:21, Marc-Andr=C3=A9 Lureau wrote:
>>> Yeah, I tried a few of those approaches. Here the problem is that
>>> QObject doesn't have base field. So you get a compile time error with
>>> a QObject * as argument.
>>
>> So the compiler requires &(x)->base to resolve even when it is not on =
the
>> branch that gets selected?
>=20
> Unfortunately, yes, all branches must compile apparently (I know)...

Ugh, and that's indeed true of _Generic too.  These don't compile:

  struct s1 { int y; };
  struct s2 { int z; };

  #define f(x)  _Generic(x, struct s1: (x).y, struct s2: (x).z)

  int f1(struct s1 *s) { return f(*s); }
  int f2(struct s2 *s) { return f(*s); }

:(  Then I guess Marc-Andr=C3=A9's realization is ugly but unavoidable.

Paolo