Add a CONFORM function to check that argument dimensions match?

10

Actually no. There is hardly any good use case for dummy arguments of CLASS(*) unlimited polymorphic type in Fortran. CLASS(*) is a pathway toward vulnerabilities in a library.

Instead one can argue this is a passable use case for the other type of unlimited polymorphic entity, TYPE(*) i.e., assumed-type dummy argument facility introduced in the language starting Fortran 2018: This is given the guardrails provided in the standard with assumed-type dummy arguments - there isn’t much a Fortranner inclined heavily toward domain expertise as opposed to sound software engineering can do with this type.

And also assumed-rank facility can be employed here.

module m
contains
   pure function conform(mold, var)
      ! Argument list
      type(*), intent(in) :: mold(..)          !<-- assumed-type, assumed-rank dummy
      type(*), intent(in), optional :: var(..) !<--       -ditto-
      ! Function result
      logical :: conform
      conform = .true.
      if ( present(var) ) then
          conform = all( shape(mold) == shape(var) )
      end if
   end function conform
end module
   use m, only : conform
   blk1: block
      integer :: foo, bar
      print *, "Block: scalar integers"
      print *, "conform(foo,bar)? ", conform(foo, bar), "; expected is T"
   end block blk1
   print *
   blk2: block
      character(len=1), dimension(2) :: foo, bar
      print *, "Block: shape=[2] character variables"
      print *, "conform(foo,bar)? ", conform(foo, bar), "; expected is T"
   end block blk2
   print *
   blk3: block
      real :: foo(1,2), bar(2,1)
      print *, "Block: rank-2 real variables of different shape"
      print *, "conform(foo,bar)? ", conform(foo, bar), "; expected is F"
   end block blk3
   print *
   blk4: block
      type :: t
      end type t
      type(t), dimension(2,3,4) :: foo, bar
      print *, "Block: rank-3 objects of type(t) with same shape"
      print *, "conform(foo,bar)? ", conform(foo, bar), "; expected is T"
   end block blk4
end

See below with both Intel Fortran and gfortran:

C:\temp>ifort /standard-semantics /warn:all /stand:f18 p.f90
Intel(R) Fortran Intel(R) 64 Compiler Classic for applications running on Intel(R) 64, Version 2021.2.0 Build 20210228_000000
Copyright (C) 1985-2021 Intel Corporation. All rights reserved.

Microsoft (R) Incremental Linker Version 14.27.29112.0
Copyright (C) Microsoft Corporation. All rights reserved.

-out:p.exe
-subsystem:console
p.obj

C:\temp>p.exe
Block: scalar integers
conform(foo,bar)? T ; expected is T

Block: shape=[2] character variables
conform(foo,bar)? T ; expected is T

Block: rank-2 real variables of different shape
conform(foo,bar)? F ; expected is F

Block: rank-3 objects of type(t) with same shape
conform(foo,bar)? T ; expected is T

C:\temp>gfortran -Wall p.f90 -o gcc-p.exe

C:\temp>gcc-p.exe
Block: scalar integers
conform(foo,bar)? T ; expected is T

Block: shape=[2] character variables
conform(foo,bar)? T ; expected is T

Block: rank-2 real variables of different shape
conform(foo,bar)? F ; expected is F

Block: rank-3 objects of type(t) with same shape
conform(foo,bar)? T ; expected is T

C:\temp>

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