Re: lack of const in glib::GDate

[Havoc Pennington <hp redhat com>]

Ben Stanley <bds02 uow edu au> writes:
> 
> I'm using the GDate stuff in glib-1.2.9, and I noticed that const has
> not been used
> anywhere.
> 
> I was wondering if there was a reason that it was designed that way, and
> if there are any plans for changing it in the future.
> 
> I also noticed that const has been used in other places in the API.
> 

Many of the const operations on GDate actually do mutate the struct,
because GDate has two different representations of the date which it
keeps updated according to what you're doing. C has no mutable
keyword. If you have a 'const GDate' then it could be in read-only
memory, and the GDate methods would crash.

Basically const isn't worth much on plain structs, because of no
'mutable', and also because of this:

 struct Foo
 {
   gchar *field;
 };

const Foo *foo = foo_new ();
foo->field[0] = 'a'; /* no warning at all */

i.e. the const isn't "inherited" by member variables. This is why
const is useless on GList, for example:

 GList *list;
 const GList *clist;

 list = clist->next->prev; /* no warning, and list == clist. */

Anyhow, short answer, the reason C programmers don't use const is that
without C++ features such as mutable and accessor functions, const is
not very useful.

Havoc