[vhdl-200x-ft] Update FT 22 composite locally static values

FT22 has been updated to reflect the needs of array bounds to be locally static
if the resulting expression is to be locally static.

Regards,
    John

-- 
-- mailto: johnr@model.com     phone: (503)685-0864
--   http://www.model.com        fax: (503)685-0921
--

IEEE 200X Fast Track Change Proposal

ID: FT-22

Proposer: John Ries
email: johnr@model.com

Status: Open
Proposed: 04/20/04
Analyzed: Date
Resolved: Date

Enhancement Summary: Allow aggregates, array operands, and array operators
to be locally static.
Related issues:
Relevant LRM section: 7.4.1

Enhancement Detail:
----------------------------

Currently the only locally static non-scalars are bit string literals
and string literals. As a result aggregates, concatenation, slices,
or functions returning composites cannot be used in places that
require locally static expression such as choices for cases.

This enhancement is to modify the statement

  "An expression is said to be locally static if and only if every
  operator in the expression denotes an implicitly defined operator
  whose operands and result are scalar and if every primary in the
  expression is a locally static primary, where locally static primary
  is defined to be one of the following:"

To

  "An expression is said to be locally static if and only if every
  operator in the expression denotes an implicitly defined operator
  and if every primary in the expression is a locally static primary,
  where locally static primary is defined to be one of the following:"

Item b in the list is modified to

b) A constant (other than a deferred constant) explicitly declared by
   a constant declaration with a locally static subtype and initialized
   with a locally static expression.

The line 606 in section 7.4.1 is changed from

"A locally static array subtype is a constrained array subtype formed
  by imposing on an unconstrained array type a locally static index
  constraint"

to

"A locally static array subtype is a constrained array subtype formed
 by imposing on an unconstrained array type with a locally static index
 constraint. The unconstained array type must have a locally static element subtype
 and locally static index subtype definitions."

Addition items defining a locally static primary would be added

  "k) An array aggregate, if and only if

      1) All expression in its element associations are locally static
         expressions, and
      2) All ranges in its element associations are locally static
         ranges

   l) A record aggregate, if and only if all expressions in its
      element associations are locally static expressions

   m) A subelement or a slice of a locally static primary, provided
      that any index expressions are locally static expressions and any
      discrete ranges used in slice names are locally static discrete
      ranges

A locally static range is either a range of the second form (see 3.1) whose
bounds are locally static expressions, or a range of the first form whose prefix
denotes either a locally static subtype or and object that is of a locally static
subtype. A locally static range constraint is a range constraint whose range is
locally static.

   n) A selected name, whose prefix denotes a locally static primary."

These changes allow better use of existing language construct at the
expense of compiler complexity. Specifically the inability to use
& in constants that are then used as case choices currently is illegal
and causes users problems.

Analysis:
----------------------------
[To be performed by the 200X Fast Track Working Group]

Resolution:
----------------------------
[To be performed by the 200X Fast Track Working Group]
Received on Mon Nov 15 16:06:48 2004