[Mpi-forum] "BigCount" rendering in PDF

[Jeff Hammond]

You’re going to have to mention C++. You can’t just pretend that C++ supports C11 generic, because it explicitly doesn’t. And you really should do this because it’s ridiculous not to use C++ polymorphism if we use C11’s.

Jeff

> On Jul 31, 2019, at 6:14 AM, Jeff Squyres (jsquyres) via mpi-forum <mpi-forum at lists.mpi-forum.org> wrote:
> 
>> On Jul 31, 2019, at 4:31 AM, Joseph Schuchart via mpi-forum <mpi-forum at lists.mpi-forum.org> wrote:
>> 
>> Should we mark in the interface the fact that the MPI_Count overloads are only available in C11? I'm thinking about something similar to cppreference's distinction between C/C++ standard versions, e.g.,
>> 
>> 
>> ```
>> int MPI_Send(const void *buf, MPI_Count count, MPI_Datatype datatype, int dest, int tag, MPI_Comm comm) [>C11|C++]
>> ```
> 
> These are exactly the kind of discussions that I'd like to have before the September meeting: what is the best way to render the output to convey the information in an aesthetic way?  I'm terrible at this kind of stuff.
> 
> -----
> 
> That being said, I would not want to mark anything as "C++", because the MPI spec does not explicitly support C++ at all.  The text that will support this ticket will only have an Advice to Implementors for those implementations who want to continue to have an <mpi.h> that supports both C and C++.  Per feedback we got in the Virtual Meeting last week, the advice is to *not* use C++ polymorphism, and, instead, treat C++ as a complier that does not support C11 _Generic (i.e., the MPI_Count-enabled version of MPI_Foo() will simply not be available -- see Froozle).
> 
> The rationale here is that if an implementation supports C++ polymorphism, there are three options:
> 
> 1. The standard needs to make official statements about C++, which basically re-introduces formal C++ support in the MPI spec (which is a Big Deal)
> 2. PMPI-enabled tools will need to support non-standard C++ polymorphism in order to guarantee that they can intercept all MPI APIs when the application is written in C++
> 3. PMPI-enabled tools do not support intercepting all MPI APIs when the application is written in C++
> 
> None of those 3 options are attractive.
> 
> -- 
> Jeff Squyres
> jsquyres at cisco.com
> 
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