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Barry Smith <bsm...@petsc.dev> writes:
>> We already have the generated ftn-auto-interfaces/*.h90. The INTERFACE keyword could be replaced with CONTAINS (making these definitions instead of just interfaces), and then the bodies could use iso_c_binding to call the C functions. That would reduce repetition and be the standards-compliant way to do this. > > Sure, the interface and the stub go in the same file instead of two files. This is slightly nicer but not significantly simpler, and alone, it is not reason enough to write an entire new stub generator. I agree, but if one *is* writing a new stub generator for good reasons (like better automation/completeness), there's a case for doing it this way unless users really need an environment in which that feature can't be used. >> What we do now with detecting the Fortran mangling scheme and calling conventions "works" but doesn't conform to any standard and there's nothing stopping Fortran implementations from creating yet another variant that we have to deal with manually. > > From practical experience, calling C/Fortran using non-standards has only gotten easier over the last thirty-five years (fewer variants on how char* is handled); it has not gotten more complicated, so I submit the likelihood of "nothing stopping Fortran implementations from creating yet another variant that we have to deal with manually" is (though possible) rather unlikely. As far as I am concerned, much of iso_c_binding stuff just solved a problem that never really existed (except in some people's minds) since calling C/Fortran has always been easy, modulo knowing a tiny bit of information.. An examples for concreteness: https://urldefense.us/v3/__https://fortranwiki.org/fortran/show/Generating*C*Interfaces__;Kys!!G_uCfscf7eWS!YxEvDc1D4VU4lVeRBtAnpLnK6bOtF5usV8GsUXqiSsukaNrK5znZB16c7n5VUgIqFwNTGEkSEppdwFVuJSM$ And discussion: https://urldefense.us/v3/__https://fortran-lang.discourse.group/t/iso-c-binding-looking-for-practical-example-of-how-it-helps-with-mangling/3393/8__;!!G_uCfscf7eWS!YxEvDc1D4VU4lVeRBtAnpLnK6bOtF5usV8GsUXqiSsukaNrK5znZB16c7n5VUgIqFwNTGEkSEppdx1pKPgQ$ With this approach, one could even use method syntax like ksp%SetOperators(J, Jpre), as in the nlopt-f project linked in the top of this question. I don't know if we want that (it would be a huge change for users, albeit it "easy"), but generating stubs in Fortran using iso_c_binding opens a variety of possibilities for more idiomatic bindings.
