J3/04-111

Date:    08 Dec. 2003
To:      J3
From:    Dan Nagle
Subject: Automatic for Procedure Variables


Many vendors support an "automatic" declaration for procedure
variables to indicate the opposite of "save", that is, that
there is to be a new instance of each variable for each instance
of the procedure.  This applies to recursive procedures as well as
multihtreaded programs.

I want to avoid module variables so as not to complicate modules.

Number:

Title: Automatic Procedure Variables

Submitted By: J3

Status: For Consideration

References: Section 5.1.2.13 SAVE

Basic Functionality: Request a new instance of a variable for each
                     instance of a procedure.

Rationale:  The standard currently provides the SAVE attribute
            to request persistent storage for a variable, but
            no way exists within the standard to request per instance
            of the procedure storage.  Many vendors have implemented
            an AUTOMATIC attribute to fulfill this requirement.
            This paper proposes to standardize this attribute
            for procedure variables only.

Estimated Impact: The effect should be low, since vendors must implement
                  recursive procedures anyway, and many have implemented
                  automatic already.

Detailed Specification: The automatic attribute would parallel the save
                        attribute.  It may be placed on the declaration
                        statement, or applied to a list or to an entire
                        procedure if no list is present.

                        Example:

                        real, automatic :: x, y( 100)

History: