The G_CONST_RETURN define in GLib is, and has always been, a bit fuzzy.
We always used it to conform to the platform, at least for public-facing
API.
At first I assumed it has something to do with brain-damaged compilers
or with weird platforms where const was not really supported; sadly,
it's something much, much worse: it's a define that can be toggled at
compile-time to remove const from the signature of public API. This is a
truly terrifying feature that I assume was added in the past century,
and whose inception clearly had something to do with massive doses of
absynthe and opium — because any other explanation would make the
existence of such a feature even worse than assuming drugs had anything
to do with it.
Anyway, and pleasing the gods, this dubious feature is being
removed/deprecated in GLib; see bug:
https://bugzilla.gnome.org/show_bug.cgi?id=644611
Before deprecation, though, we should just remove its usage from the
whole API. We should especially remove its usage from Cally's internals,
since there it never made sense in the first place.
Remove the dispose() implementation and replace
with destroy().
This should be promoted as the standard approach
for implementing a composite actor, as it emits a
signal when instances of the actor subclass are destroyed.
Add some extra description to the allocate() function,
explaining how the allocation has to be adjusted to
coordinates relative to the actor as a whole, before
applying to the single child actor it is composed from.
As most actor subclasses will probably want to implement
size requisition, give a simple example of how to do this
on the basis of the composed actor's size, plus some padding.
