[MPI3 Fortran] Fortran extra_state argument to MPIattributefunctions
nmm1 at cam.ac.uk
Thu May 28 15:36:36 CDT 2009
On May 28 2009, Aleksandar Donev wrote:
>> Using tokens for such things
>> has major software engineering advantages, not least because you can
>> check them for validity (e.g. scoping errors) before use.
>Except that *integers* are the wrong way to do that! If they were, we
>would call them "tokens" and not "integers". Sets are sets, and integers
>are some particular set which has, for example, addition attached to it,
>something tokens probably not ought to.
Oh, yes, I agree. Opaque types would be better.
>> Even in C,
>> checking arbitrary pointer values for validity relies on undefined
> Correct, and languages more modern than C, including Fortran 2003, have a
> good (maybe not the best) way to do "checked" pointers, namely, using
> "CLASS(...), POINTEr". These are (partially) typed, and can only be
> pointed to things of the right type and with the TARGET attribute, but
> are also extensible. You can make them act like integers and thus be even
> more checkable (for example, restricted to a small finite set of possible
> values), or TYPE(C_PTR) (an address), according to your desires. Instead
> of forcing everyone to use integers just because that happens to be the
> one single intrinsic type that can be used to index a set.
But can they handle the scoping issue?
>But the point here is to find something for MPI. In most MPI codes, I am
>sure people will not check the integer handles and in fact simply do
>illegal things like Jeff mentioned: pass the first element of an array
>and that way later refer to the whole array. Also, the C interface
>already uses void*, and trying to do "better" than that seems pointless.
>I though the decision was not to "modernize" the MPI interface but
>rather try to emulate the C interface as closely as possible.
Jeff Squyres has responded to this one, and I think that we should follow
up on that.
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