>From my perspective, one of the beauties of Fortran 90 is infact that
in the majority of cases it is not necessary to define an explicit
interface and thus there is no need to maintain consistent
specifications of procedures (public or private) in more than one
place. Thus I would be disappointed to see the
compulsory separation of implementation and specification
(interface).
Never-the-less Fortran 90 does have a problem with respect to the
way Modules are implemented which can (and does) lead to very large
source files.
For example, often, one requires that instances of a derived type be
declared outside the Module in which the type is defined. But is also
usually required that the components of the type be invisible to the
outside. In such circumstances it is necessary that all procedures
that operate on this type be contained in the Module in which the
type is defined, thus leading to impractically large source files.
It would seem to me that a mechanisim is required which allows one to
define a type in one Module (file) as PUBLIC with PRIVATE components
and to be able to specify other Modules (files) for which the PRIVATE
components can infact be accessed. This would allow one to partition
the development of a system into smaller and more managable
components, while at the same time preserving the OO ideas of
encapsulation and hiding implementation details.
The following pseudo code in which the new constructs UMBRELLA
and UNDER are introduced is intended to illustrate my objectives.
In this scheme, the UMBRELLA becomes the unit of "Object Oriented" or
"logical" encapsulation and MODULES serve as a convenient means
of partitioning a system. However, there is nothing to stop Modules
being used in the same way that they are currently.
I have no experience in language design or implementation. What
follows is from a user perspective, and so would welcome suggestions
for improvement.
=== Pseudo code follows ===
! ... Define an UMBRELLA (MySystem) which USEs Modules
! which may be in different files. The entities within a
! Module which is UNDER MySystem are visible (PUBLIC) to
! all other entities within all other Modules which are
! also UNDER MySystem.
UMBRELLA MySystem
! ... This UMBELLA contains the declaration of the type MyType and
! and all the procedures which operate on it.
USE MyTypeModule
USE MyPublicModuleA
USE MyPublicModuleB
USE MyPrivateModuleA
USE MyPrivateModuleB
END UMBRELLA MySystem
MODULE MyTypeModule
! ... Declare that MyTypeModule is UNDER the MySystem UMBRELLA
UNDER MySystem
PUBLIC
! ... MyType is PUBLIC but its components are PRIVATE, except in
! those modules UNDER the MySystem UMBRELLA, where the
! components are PUBLIC.
TYPE :: MyType
PRIVATE
INTEGER :: componentA
...
END TYPE MyType
...
END MODULE MyTypeModule
MODULE MyPublicModuleA
UNDER MySystem
! ... The following modules are UNDER the MySystem UMBRELLA.
USE MyTypeModule
USE MyPrivateModuleA
! ... The following modules are "normal" modules
USE OtherModuleA
PUBLIC
CONTAINS
SUBROUTINE SubA(x)
TYPE(MyType), INTENT(IN) :: x
...
! ... components of x are visible within MyPublicModuleA
! because this module is UNDER the MySystem UMBRELLA
! of which MyTypeModule is a part.
x%componentA = 1
! ... PrivSubA is visible, again because it is UNDER the
! MySystem UMBRELLA
CALL PrivSubA(x)
END SUBROUTINE SubA
...
END MODULE MyPublicModuleA
! ... Similar for MyPublicModuleB etc.
MODULE MyPrivateModuleA
UNDER MySystem
USE MyTypeModule
! ... All subroutines in this module are PRIVATE except in those
! modules UNDER the MySystem UMBRELLA, in which they are
! PUBLIC.
PRIVATE
CONTAINS
SUBROUTINE PrivSubA(x)
TYPE(MyType), INTENT(IN) :: x
...
x%componentA = ...
END SUBROUTINE PrivSubA
...
END MODULE MyPrivateModuleA
! ... Similar for MyPrivateModuleB etc.
MODULE SomeOtherModule
USE MyTypeModule
USE MyPublicModuleA
CONTAINS
SUBROUTINE SomeSub(x)
TYPE(MyType) :: x
! ... The components of x cannot be accessed because
! SomeOtherModule is not UNDER MySystem.
! Similarly, PrivSubA can not be called from this Module.
! However, SubA can be called because it was declared
! to be PUBLIC in MyPublicModuleA.
CALL SubA(x)
END SUBROUTINE SomeSub
END MODULE SomeOtherModule
Regards,
David.
----------------------------------------------------------
David Vowles
Research Officer
Department of Electrical and Electronic Engineering
The University of Adelaide
Australia 5005
Voice: +61 8 8303 5416
Fax: +61 8 8303 4360
Email: [log in to unmask]
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