(j3.2006) 17-152 and CO_REDUCE

[Bill Long]

This is another example of gratuitous generality that serves no purpose.  We have made that mistake enough times in the past that we should know better than to fall for it again.

In this particular case, there is a very good reason why these changes cannot work.  The OPERATION function is called from within the CO_REDUCE library code. Which is almost certainly going to be written in C or C++.  Independent of the library implementation language, there is no chance that an interface for the function would be visible at the call site.  Thus, the interface has to be fixed in the standard.  So, optional arguments are unacceptable.  A library routine would have no concept of how to call the function with a Fortran polymorphic argument, so that is also out. 

Cheers,
Bill

> On May 17, 2017, at 9:06 PM, Van Snyder <Van.Snyder at jpl.nasa.gov> wrote:
> 
> Imposing "exactly two arguments" on the OPERATION argument to CO_REDUCE
> requires one to write a wrapper to use a function that has more than two
> arguments, with those after the first two being optional.
> 
> I would prefer "OPERATION shall be a pure function with at least two
> arguments; the result and each of the first two arguments shall be
> scalar, nonallocatable, nonpointer, nonpolymorphic data objects with the
> same type and type parameters as A.  The first two arguments shall not
> be optional and any additional arguments shall be optional."
> 
> I also don't understand why the first two arguments can't be optional.
> 
> Are polymorphic dummy arguments really a problem?  If not, remove the
> prohibition against polymorphic, and replace "type" with "declared
> type".
> 
> If the processor is expected to enforce the requirements on OPERATION,
> it should be required to have explicit interface.
> 
> 
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Bill Long                                                                       longb at cray.com
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