Re: g_object_ref() now propagates types

2017-12-11 Thread Owen Taylor 
On Fri, Dec 8, 2017 at 6:26 AM, Philip Withnall 
wrote:

>
> child_type = CHILD_TYPE (g_object_ref (parent_type));
>
> That will add a compile-time explicit cast, and a runtime type check.
> (As always, the runtime type check is disabled if GLib is built without
> debugging enabled (or with G_DISABLE_CAST_CHECKS defined.)
>

G_DISABLE_CAST_CHECKS is defined internally in GLib and GTK+ for stable
releases (--enable-debug defaults to minimum for stable releases, yes for
unstable releases), but that doesn't have any effect on whether they are
enabled or disabled for your application; if you want to disable cast
checks in production builds for your application, you need to specify
G_DISABLE_CAST_CHECKS yourself.

Owen
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Re: g_object_ref() now propagates types

2017-12-11 Thread Philip Withnall 
On Sat, 2017-12-09 at 10:54 +0100, Sébastien Wilmet wrote:
> On Fri, Dec 08, 2017 at 11:26:31AM +, Philip Withnall wrote:
> > Note that the new behaviour requires GCC, and is only enabled if
> > you
> > have defined GLIB_VERSION_MAX_ALLOWED >= GLIB_VERSION_2_56.
> 
> If GLIB_VERSION_MAX_ALLOWED is not defined, does it take by default
> the
> value of the last GLib version?

That’s a good point. If left undefined, GLIB_VERSION_MAX_ALLOWED is
defined to the current stable release (GLIB_VERSION_CUR_STABLE). Once
2.56 is released, that means anyone who has not defined
GLIB_VERSION_MAX_ALLOWED will get the new g_object_ref() behaviour by
default.

Philip

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Re: g_object_ref() now propagates types

2017-12-09 Thread Sébastien Wilmet 
On Fri, Dec 08, 2017 at 11:26:31AM +, Philip Withnall wrote:
> Note that the new behaviour requires GCC, and is only enabled if you
> have defined GLIB_VERSION_MAX_ALLOWED >= GLIB_VERSION_2_56.

If GLIB_VERSION_MAX_ALLOWED is not defined, does it take by default the
value of the last GLib version?

--
Sébastien
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Re: g_object_ref() now propagates types

2017-12-08 Thread Paul Davis 
On Fri, Dec 8, 2017 at 6:26 AM, Philip Withnall 
wrote:

> Hi all,
>
> We just landed a patch in GLib which propagates the type from the
> argument of g_object_ref() to its return type:
>
> https://git.gnome.org/browse/glib/commit/?id=3fae39a5d
> https://bugzilla.gnome.org/show_bug.cgi?id=790697
>
> The idea here is that it will catch invalid implicit casts which the
> compiler otherwise wouldn’t have noticed because g_object_ref()
> previously operated entirely on gpointers. This will eliminate a whole
> class of bugs: bugs which are unlikely to exist, but are a complete
> pain to track down if they do.
>

​Great work. Another 3 or 4 or 200 of these and we'll almost have a C++
compiler!

tongue firmly and warmly in cheek :))) ​
​
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Re: g_object_ref() now propagates types

2017-12-08 Thread Emmanuele Bassi 
On 8 December 2017 at 11:26, Philip Withnall  wrote:


> If anybody encounters any problems with this, please comment on the bug
> report:
>
> https://bugzilla.gnome.org/show_bug.cgi?id=790697

As a side note: I've started a full Continuous rebuild, so if there
are projects that indeed break with this change, we should be notified
pretty quickly.

Ciao,
 Emmanuele.

-- 
https://www.bassi.io
[@] ebassi [@gmail.com]
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g_object_ref() now propagates types

2017-12-08 Thread Philip Withnall 
Hi all,

We just landed a patch in GLib which propagates the type from the
argument of g_object_ref() to its return type:

https://git.gnome.org/browse/glib/commit/?id=3fae39a5d
https://bugzilla.gnome.org/show_bug.cgi?id=790697

The idea here is that it will catch invalid implicit casts which the
compiler otherwise wouldn’t have noticed because g_object_ref()
previously operated entirely on gpointers. This will eliminate a whole
class of bugs: bugs which are unlikely to exist, but are a complete
pain to track down if they do.

The downside of this is that some legitimate implicit casts may now
cause compiler warnings with -Wincompatible-pointer-types. For example,
in the situation below, a warning will be introduced since parent_type
isn’t guaranteed to be an instance of child_type:

ParentType *parent_type;
ChildType *child_type;

child_type = g_object_ref (parent_type);

To fix this warning, first double-check that parent_type is actually
guaranteed to always be an instance of child_type at runtime, and then
change the ref to:

child_type = CHILD_TYPE (g_object_ref (parent_type));

That will add a compile-time explicit cast, and a runtime type check.
(As always, the runtime type check is disabled if GLib is built without
debugging enabled (or with G_DISABLE_CAST_CHECKS defined.)

Note that the new behaviour requires GCC, and is only enabled if you
have defined GLIB_VERSION_MAX_ALLOWED >= GLIB_VERSION_2_56.

If anybody encounters any problems with this, please comment on the bug
report:

https://bugzilla.gnome.org/show_bug.cgi?id=790697

Thanks,
Philip
on behalf of the GLib maintainership cabal

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