ISO/IEC JTC1/SC22/WG5 N1355
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To: WG5
From: Data Subgroup
Author: Lawrie Schonfelder
Subject: Simplification of requirement
Date:17-JUN-1999

WG5, during its consideration of the current requirements and work-plan for the production of
Fortran2000, considered that a significant saving could be achieved by the following changes.

¥	The current description of function and language definition included in the draft document
for data-object initialisation (constructors) should be removed.

¥	The current functionality and description for object finalisation (destruction) should be
retained, perhaps with some modification and correction.

¥	To add at least some minimal compensatory functionality for the lost capability, the
following relaxation should be made. Users should be permitted to override the intrinsic data-
type structure constructor by the creation of procedures with a generic name that is the same as
the type-name. The same rules should be applied, mutatis mutandis, as already exist for
overriding intrinsic definitions for the semantics of intrinsic assignment and intrinsic functions
by user written generic procedures.

It is accepted that this loses some potentially useful functionality but it is believed that such a
change would make a substantial reduction in J3Õs workload, while preserving much of the
critical capability of the constructor/destructor requirement.

Although this proposal will not in general allow the creation of user defined derived type
objects with the PARAMETER attribute, nor will it make initialisation more generally
supportable.  It will, however, allow appropriately named user-defined type-conversion
procedures to be used to create values of derived types.  For example, given a type definition
for variable precision arithmetic based on a type,

TYPE NUMBER
  INTEGER::exp
  INTEGER,POINTER::sig(:)
END TYPE NUMBER

The user could define additional generic procedures called NUMBER.  One specific version
could take a single integer argument and another could take a character string argument; both
designed to return a value of the NUMBER datatype.  This will allow the following set of
statements to be valid.

type(NUMBER)::ten,c
ten=NUMBER(10)
c=NUMBER("2.99792458E+8") 

With a data type such as this the user has no simple way of using the intrinsic value
constructors to create the structure values.  Usable values can only be created by procedures
written by the user to provide a more appropriate type conversion.   In general, the logical name
for such conversion procedures is the typename.  In this example the name NUMBER is the
appropriate.
  
This minor change provides a valuable regularisation and aid to program readability and does
not preclude the later addition of more extensive constructor functionality.