J3/15-117
To:        J3
Subject:   Wart removal proposal -- Specify type parameters with EXTENDS
From:      Van Snyder
Date: 2015 January 29
Reference: 15-007

1. Introduction
===============

The syntax of the EXTENDS attribute of a derived type definition uses
<parent-type-name>.  This does not allow to specify type parameters of
the parent type, which could be used to prohibit them from being
specified differently when variables of the extension type are declared.

2. Proposal
===========

In R428 (in 15-007), replace <parent-type-name> with
<derived-type-spec>.  Define the effects of this change.

3. Edits
========

[xviii, Introduction, under "Data usage and computation"] Insert list
item

"-- Where a type is extended, values of type parameters of the parent
    type may be specified; these parameters are then not parameters of
    the extension type."

[64:6 R428] Replace "<parent-type-name>" with "<derived-type-spec>".

[64:11 C433] Replace the constraint:

"C433 (R428) The <type-name> in <derived-type-spec> shall be the name of
      an accessible extensible type (4.5.7)."

[64:11+ C433+] Insert a constraint:

"C433a (R428) Every <type-param-value> within <derived-type-spec> shall
       be specified by a constant expression."

[79:23- 4.5.7.1p3-] Insert a paragraph:

"If <type-param-spec-list> appears within <derived-type-spec> in the
EXTENDS <type-attr-spec>, it specifies values for the specified type
parameters of the parent type.  Those parameters of the parent type are
not parameters of the extension type."