J3/05-239

Date:  July 25, 2005
To:    J3
From:  Aleksandar Donev
Title: Storage units and STORAGE_SIZE inquiry function

References: J3 proposal J3-004 in WG5 Repository

Basic Functionality:

  Modify the original STORAGE_SIZE proposal to allow for arguments that
are
  1) Of arbitrary declared derived type, and
  2) Polymorphic, including unlimited polymorphic
  To do this some extension to 16.4.3.1 will need to be done in order to
explain what a storage unit means in such contexts.

  The procedure STORAGE_SIZE is in ISO_FORTRAN_ENV and returns the size
in bits of the storage unit for a scalar with the same type as the
*dynamic* type of its argument, as specified in 16.4.3.1. Without the
proposed modification, I believe the utility of this function is too
small and covers only a small subset of existing demand.

Rationale:

  There are situations where a program needs to know the size of an
entity.

Estimated Impact:

   Many vendors already provide extensions similar to this. The standard
will hopefully be impacted in a minimal way localized in 16.4.3.

Detailed Specification:

   It seems some addition to 16.4.3.1 is necessary in order to clarify
the concept of a storage unit in certain cases. The problem at present
seems to be the leading "In a storage association context" before the
numbered list in 16.4.3.1 [from private discussion with Richard]. This
wording excludes things like polymorphic objects as such cannot occur
in a storage association context. This wording is likely there in order
to clarify things like the fact that holding a variable in register
does not give it a different storage unit. I ask J3 to consider the
issue and come up with a recommendation.

   Here is the original spec for STORAGE_SIZE:

__________________________________
      *Description.*  Returns the storage size in bits for a
                      nonpointer nonallocatable scalar
                      of the declared type of X.

      *Class.*  Inquiry function.

      *Arguments.*

        X               may be of intrinsic or derived type.  It
                        shall not be polymorphic.  If it is
                        of derived type, that type shall be
                        a SEQUENCE or interoperable type and
                        shall have no allocatable ultimate
                        components.  If its type has
                        any deferred type parameters, it shall
                        be a pointer that is associated or
                        an allocatable object that is
                        allocated. It may be a scalar or an array.

        *Result Value.*  The result value is the size in bits
                         of the storage unit (16.4.3.1)
                         in a storage association context
                         for a nonpointer nonallocatable scalar
                         with the declared type and
                         type parameters of X.
__________________________________


The modification should be:

__________________________________

   *Description.*  Returns the storage size in bits for a nonpointer
nonallocatable scalar of the dynamic type of X.

   *Arguments.*
   X may be of intrinsic or derived type, and it may be polymorphic. It
may be a scalar or an array. If it is pointer or allocatable and it is
polymorphic or its type has any deferred type parameters, it shall be a
pointer that is associated or an allocatable object that is allocated.

   *Result Value.*  The result value is the size in bits of the storage
unit (16.4.3.1) in a storage association context for a nonpointer
nonallocatable scalar with a declared type and type parameters that are
the same as the dynamic type of X.
__________________________________


History: J3/05-239 at meeting 173

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