Re: [RFC] timers, pointers to functions and type safety

[Kyle Moffett]

On Dec 02, 2006, at 07:42:51, Al Viro wrote:
> On Sat, Dec 02, 2006 at 04:23:32AM -0500, Kyle Moffett wrote:
> > On Dec 01, 2006, at 12:21:49, Al Viro wrote:
> > > And that's where it gets interesting.  It would be very nice to  
> > > get to
> > > the following situation:
> > >  * callbacks are void (*)(void *)
> > >  * data is void *
> > >  * instances can take void * or pointer to object type
> > >  * a macro SETUP_TIMER(timer, func, data) sets callback and data  
> > > and checks if func(data) would be valid.
> >
> > This is where a very limited form of C++ templates would do  
> > nicely; you could define something like the following:
> >
> > template <typename T>
> > static inline void setup_timer(struct timer_list *timer,
> > 		void (*function)(T *), T *data)
> > {
> > 	timer->function = (void (*)(void *))function;
> > 	timer->data = (void *)data;
> > 	init_timer(timer);
> > }
> >
> > Any attempts to call it with mismatched "function" and "data"  
> > arguments would display an "Unable to find matching template"  
> > error from the compiler.
> >
> > Unfortunately you can't get simple templated functions without  
> > opening the whole barrel of monkeys involved with C++ support;
>
> Fortunately, you can get all checks done by gcc without involving C+ 
> + (or related flamewars).  See original post for a way to do it in  
> a macro and for fsck sake, leave gcc@xxxxxxxxxxx out of it

Oh, I'm sorry I totally missed the CC of gcc@xxxxxxxxxxxx  My point  
was just that while it _could_ be done with GCC and some ugly macros,  
a basic form of C++ templates usually produces much nicer and more  
descriptive error messages (leaving out all the reasons C++ isn't  
usable in the kernel for the sake of academic discussion).  The  
template syntax is also a bit more descriptive than is the macro  
syntax for achieving the same thing.

Cheers,
Kyle Moffett

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