g_object_ref() now propagates types

Hi all,

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


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

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


on behalf of the GLib maintainership cabal

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