Re: Visibility attribute

[Geoff Keating <geoffk at geoffk dot org>]

Matt Austern <austern@apple.com> writes:

>   3. The later declaration always overrides the earlier.  So x and z
> have default visibility, y has protected visibility.
...
> Option 3 is what the compiler
> currently does.

As I commented in the bug report, the compiler doesn't currently do it
right; except in unit-at-a-time mode, anything between the
declarations will be compiled assuming the initial visibility.

However, this can only cause trouble in certain cases.  As I think HJ
was trying to say, maybe the best choice is an 'option 6':

6. If the later declaration has more restrictive visibility that the
   earlier, the later declaration overrides; otherwise, the visibility
   from the earlier declaration is used.

So, from your examples,

    __attribute__ ((visibility("hidden"))) int x;
    int x = 5;  // is still 'hidden'

    __attribute__ ((visibility("hidden"))) int y;
    __attribute__ ((visibility("protected"))) int y = 5;

    __attribute__ ((visibility("hidden"))) int z;
    __attribute__ ((visibility("default"))) int z = 5;

all three variables end up 'hidden', since that's the most restrictive.

Perhaps a warning when a visibility attribute is explicitly specified
and is ignored; but that's not essential.

-- 
- Geoffrey Keating <geoffk@geoffk.org>