Daniel provides improved P/R

xml/issue3975.xml

@@ -17,13 +17,53 @@ would need to have (e.g., it does not provide a means to initialize the expositi
 library was not designed to be able to work with user specializations of <tt>std::basic_format_context</tt>, declaring 
 such specializations should be explicitly disallowed.
 </p>
+
+<superseded>
+<p>
+This wording is relative to <paper num="N4958"/>.
+</p>
+
+<ol>
+
+<li><p>Modify the <sref ref="[format.context]"/> as indicated:</p>
+
+<blockquote>
+<p>
+-1- An instance of <tt>basic_format_context</tt> holds formatting state consisting of the formatting arguments and
+the output iterator.
+<p/>
+<ins>-?- The behavior of a program that adds specializations of <tt>basic_format_context</tt> is undefined.</ins>
+<p/>
+-2- <tt>Out</tt> shall model <tt>output_iterator&lt;const charT&amp;&gt;</tt>.
+</p>
+</blockquote>
+
+</li>
+</ol>
+</superseded>
+
+<note>2023-09-23; Daniel comments and provides improved wording</note>
+<p>
+During the reflector discussion, Dietmar pointed out that the constraint can in principle be checked statically (e.g. when the 
+Library creates or refers to an instantiation of <tt>basic_format_context</tt>), so we can reduce the rather draconian consequence of
+"undefined behaviour" to "ill-formed, no diagnostics required". Furthermore, the new wording also adds the same constraint to
+<tt>basic_format_parse_context</tt> as suggested by Tim. This is needed, since only one public constructor is specified, but
+that specification does not allow to construct an object a non-zero <tt>num_args_</tt> or with the type information necessary 
+for the <tt>check_dynamic_spec*</tt> functions, so the library has an unspecified way to realize this.
+</p>
 </discussion>
 
 <resolution>
 <p>
 This wording is relative to <paper num="N4958"/>.
 </p>
 
+<blockquote class="note">
+<p>
+[<i>Drafting note:</i> The suggested wording form is borrowed from exactly the same wording form used for <tt>allocator_traits</tt>.]
+</p>
+</blockquote>
+
 <ol>
 
 <li><p>Modify the <sref ref="[format.context]"/> as indicated:</p>
@@ -33,12 +73,27 @@ This wording is relative to <paper num="N4958"/>.
 -1- An instance of <tt>basic_format_context</tt> holds formatting state consisting of the formatting arguments and
 the output iterator.
 <p/>
-<ins>-?- The behavior of a program that adds specializations of <tt>basic_format_context</tt> is undefined.</ins>
+<ins>-?- If a program declares an explicit or partial specialization of <tt>basic_format_context</tt>, the program is ill-formed,
+no diagnostic required.</ins>
 <p/>
 -2- <tt>Out</tt> shall model <tt>output_iterator&lt;const charT&amp;&gt;</tt>.
 </p>
 </blockquote>
 
+</li>
+
+<li><p>Modify the <sref ref="[format.parse.ctx]"/> as indicated:</p>
+
+<blockquote>
+<p>
+-1- An instance of <tt>basic_format_parse_context</tt> holds the format string parsing state consisting of the format
+string range being parsed and the argument counter for automatic indexing.
+<p/>
+<ins>-?- If a program declares an explicit or partial specialization of <tt>basic_format_parse_context</tt>, the program is ill-formed,
+no diagnostic required.</ins>
+</p>
+</blockquote>
+
 </li>
 </ol>
 </resolution>