Richard Levitte - VMS Whacker <[EMAIL PROTECTED]>:
> Let me see if I got it all. So far, I've seen the following
> alternatives:
>
> 1. ignore the problem (obviously not the right thing to do :-)).
> 2. take the parameter in question as we do today, but use a union so
> the compiler will shut up (which is a fancy way of ignoring the
> problem).
> 3. whenever the passed parameter is a function pointer, use double
> indirection and assume the caller has really passed a reference
> to a function pointer.
> 4. Have the caller tuck the parameter in a union that will represent
> function pointers as well as other pointers, and pass that union
> by value.
> 5. Have the caller tuck the parameter in a union that will represent
> function pointers as well as other pointers, and pass that union
> by reference.
> Actually, 4 and 5 are basically the same.
No, 5 is to 4 what (for function pointers) 3 is to 1.
> Choices 1 and 2 are really just as bad, they're designed to ignore the
> problem instead of dealing with it.
>
> Choice 3 assumes that the parameter ni question will be prototyped
> and used like this:
>
> int foo (..., void *parg, ...)
> {
> /* ... */
> int (*fptr)() = *(int (**)())parg;
> /* ... */
> }
>
> It's a good way to deal with the problem in what could be perceived as
> a safe way, but for a detail: there's no way to see from the API that
> function pointers need to be handled differently than other pointers
> when passed down to the functino using them ("doall" and "ctrl"
> functions...), and the compiler will not give a hint.
It will give a hint! Just don't use casts, and the compiler will
complain when you try to pass a function pointer directly. Simarly,
the function using the function pointer can be written without casts
if it is using the pointer correctly; if it's incorrect, you need
casts to make the warning go away.
> And yes, there will be the problem of binary compatibility in all
> choices but 1 and 2...
Choice 4 should be binary compatible as well, because on platforms
where choice 1 and 2 work in practice both types of pointers
have the same length, so probably the union won't be any different.
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