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    SubjectRe: [PATCH 5/5] typesafe: TIMER_INITIALIZER and setup_timer
    On Thursday 06 March 2008 21:40:35 Al Viro wrote:
    > extern void decay_to_pointer(void const volatile *);
    > #define check_callback_type(f,x) (sizeof((0 ? decay_to_pointer(x),(f)(x) :
    > (void)0), 0)) #define __setup_timer(timer, func, arg) \
    > do { \
    > struct timer_list *__timer = (timer); \
    > __timer->function = (void (*)(unsigned long))(func); \
    > __timer->data = (unsigned long)(arg); \
    > (void)check_callback_type(func, arg); \
    > } while(0)

    Thanks for that snippet; it's much more complete than the last one I found.
    I especially like the handling of const- and volatile-taking callback fns.
    My version is uglier, pasted below.

    There are three problems I see here. First, the lack of warning for "void
    intfn(int); DECLARE_TIMER(t, intfn, 0);", but that's relatively minor.
    Second, the change of all the users is just churn, with cast_if_type() it can
    be done over the next couple of years, if ever.

    Worst, I can't see a way to apply your technique in general, for
    non-void-returning functions (eg. interrupt handlers).

    Here's the typesafe_cb () helper function from ccan (there are also
    typesafe_cb_preargs and postargs for callbacks with extra args):

    /* Doesn't handle const volatile, but can be added. */
    #define typesafe_cb(rettype, fn, arg) \
    cast_if_type(cast_if_type(cast_if_type((fn), \
    rettype (*)(const typeof(arg)), \
    rettype (*)(void *)), \
    rettype (*)(volatile typeof(arg)), \
    rettype (*)(void *)), \
    rettype (*)(typeof(arg)), \
    rettype (*)(void *))

    > PS: apologies for missing your previous mail; ETOOBIGMBOX ;-/

    That's fine, happens to all of us. I was a little disappointed to return from
    holiday to discover that either your work or mine hadn't been merged tho :)


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