Re: [Qemu-devel] [PATCH 2/3] qobject: assume base of a qobject is at offset 0

[Paolo Bonzini <pbonzini@redhat.com>]

On 21/03/2018 15:21, Marc-André 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?
> 
> 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-André's realization is ugly but unavoidable.

Paolo