[Freeciv-Dev] (PR#15158) __extension__ keyword in gui-sdl

["Christian Prochaska" <cp.ml.freeciv.dev@xxxxxxxxxxxxxx>]

<URL: http://bugs.freeciv.org/Ticket/Display.html?id=15158 >

> [jdorje - Sa 14. Jan 2006, 19:15:10]:
> 
> 
> I can see no reason why it would be there.  Was it always there?  Is it 
> there in 1.14?
> 
> -jason
> 

SVN history shows the following:

in r5500 (first version of the SDL client in Freeciv repository) it
looked like this

#define get_wstate(pWidget)                             \
( __extension__                                         \
        (pWidget->state_types_flags & STATE_MASK)       \
)

in r5831 the fc__extension macro was introduced and the macro above
changed to

#define get_wstate(pWidget)                             \
        fc__extension(pWidget->state_types_flags & STATE_MASK)

the Log entry says "Correct __extension__ calls."

in r5968 the scrollbar_size macro was introduced

#define scrollbar_size(pScroll)                                         \
  fc__extension((float)((float)(pScroll->active) /
(float)pScroll->count) * \
                                (pScroll->max - pScroll->min))

in r6082 the "state flags" were changed to an enum type and we got

#define get_wstate(pWidget)                             \
        fc__extension((enum WState)(pWidget->state_types_flags & STATE_MASK))

which is the current version.

So it now appears to me that the __extension__ keyword was necessary in
the first version because of the braces (when the macro was used inside
an expression)

http://gcc.gnu.org/onlinedocs/gcc-3.3.1/gcc/Statement-Exprs.html

That would mean the problem had already been solved by removing the
braces in r5831.

Ok, I think I understand now :-)

There is a problem with macros that have braces and "return a value".
Using "do{}while(0)" is not possible in this case, so you need to make
use of the GCC extension or write a function. Then Rafal created the
fc__extension macro to use with macros of this type and used it even if
there were no braces at all.

That would also make Raimar Falke's patch in PR#3608 a bit clearer to
me. So I think the fc__extension macro can be safely removed and it's
generally better to use functions instead for the kind of macros that
would have needed it. Agreed?