Assignment interfaces with allocatable polymorphic variables in gfortran 5.5.0 & 8.1.0.

[Ethan Beyak]

Janus,

Thank you very much for your response. I didn't realize you could put an
'assignment (=)' in a public statement. This'll solve my problem perfectly!

As a follow-up, let's say I did have multiple 'interface assignment (=)'
blocks in this module. Would the 'public assignment (=)' statement then
make all of assignments public then?
Is there any way to make these 'public assignment (=)' statements distinct?
I tried the following, both failed to compile on gfortran 5.5.0:

=======
interface assign_foo assignment (=)
    module procedure foo
end interface assign_foo assignment (=)

interface assignment (=) assign_foo
    module procedure foo
end interface assignment (=) assign_foo

'Error: Syntax error: Trailing garbage in INTERFACE statement'
=======

Is there any way I could apply the public attribute to the interface block
directly, or am I limited to public statements for affecting the
accessibility of interface blocks?

And a brief convention question: is it standard to omit whitespace between
'assignment' and '(=)' when writing Fortran, or is there no general
consensus?

Thanks,

Ethan

On Fri, Sep 7, 2018 at 5:56 AM Janus Weil <janus@gcc.gnu.org> wrote:

> Hi Ethan,
>
> > However, on version 5.5, I get the following errors:
> >
> > OUTPUT 2
> > =========
> > $ gfortran --version
> > GNU Fortran (Ubuntu 5.5.0-12ubuntu1) 5.5.0 20171010
> >
> > $ gfortran baz_module.f90 test_public_assignment.f90 -o test.out
> > test_public_assignment.f90:13:0:
> >
> >  wrk = e     ! invoking foo
> >  1
> > Error: Assignment to an allocatable polymorphic variable at (1) is not
> yet
> > supported
> > test_public_assignment.f90:19:0:
>
> Note that gfortran version 7 can also compile the program in its
> original form (so you don't necessarily need version 8), but
> unfortunately earlier versions fail.
>
>
> > Now I did find some workaround by setting the default accessibility of
> the
> > module to be public and explicitly declaring the complement of the set of
> > procedures and variables that I wanted to be private. I'm not sure what
> > gfortran 5.5.0 is doing to be honest, but the definition of the
> assignment
> > can be used in the calling program. Commenting out lines 5,6 and
> commenting
> > in lines 8,9 in baz_module.f90 gave me the following output on gfortran
> > 5.5.0
> >
> > OUTPUT 3
> > =========
> >  Compiler version: GCC version 5.5.0 20171010
> >  Compiler options: -mtune=generic -march=x86-64
> >  d:    4.00000000       2.00000000       1.00000000
> >  e:    8.00000000       6.00000000       4.00000000
> >  f:    32.0000000       18.0000000       8.00000000
> > =========
> >
> > So I have two questions for the gfortran community: 1) do you know why
> > inverting the module accessibility causes these assignments to work in
> > gfortran 5.5.0? It seems as if the assignment interface was made public
> > somehow, but I'm not certain.
>
> Exactly, the "public" statement makes everything in the module public
> by default. The assignment operator is private otherwise.
>
>
> > 2) can you think of any *clean* solutions to
> > this problem? I'd love backward compatibility while not going against the
> > recommended standard of private default accessibility.
>
> A more reasonable approach might be to not make everything public, but
> just the assignment interface:
>
> public assignment(=)
>
> HTH,
> Janus
>