New issue from Matt Bentley: "hive::reserve() needs Throws: element adjusted to match block min/max considerations"

Author: Dani-Hub

xml/issue4379.xml

@@ -0,0 +1,71 @@
+<?xml version='1.0' encoding='utf-8' standalone='no'?>
+<!DOCTYPE issue SYSTEM "lwg-issue.dtd">
+
+<issue num="4379" status="New">
+<title>`hive::reserve()` needs <i>Throws:</i> element adjusted to match block min/max considerations</title>
+<section>
+<sref ref="[hive.capacity]"/>
+</section>
+<submitter>Matt Bentley</submitter>
+<date>17 Sep 2025</date>
+<priority>99</priority>
+
+<discussion>
+<p>
+This issue comes from Bloomberg as part of their C++26 comments via Incits. To summarize their case, in a 
+call to `reserve(n)`, 
+</p>
+<blockquote>
+<pre>
+if (n &gt; capacity() &amp;&amp; capacity() + <i>current-limits</i>.min &gt; max_size()),
+</pre>
+</blockquote>
+<p>
+`reserve` should throw, e.g when `max_size=100`, `capacity=80`, <tt><i>current-limits</i>.min</tt> and 
+<tt><i>current-limits</i>.max</tt> are `40` and `n=90`. 
+<p/>
+In addition, in the above scenario if we increase `max_size()` to 140 and `n` to 130, 
+we can see that although we could add one block with a capacity of <tt><i>current-limits</i>.min</tt>,
+adding another would be impossible; we still cannot make <tt>capacity &gt;= n</tt> without also 
+being <tt>&gt;= max_size</tt>.
+<p/>
+This is currently not stated in the <i>Throws:</i> element. I've implemented the requested additional 
+throws and they are easily achievable.
+</p>
+</discussion>
+
+<resolution>
+<p>
+This wording is relative to <paper num="N5014"/>.
+</p>
+
+<ol>
+
+
+<li><p>Modify <sref ref="[hive.capacity]"/> as indicated:</p>
+
+<blockquote>
+<pre>
+void reserve(size_type n);
+</pre>
+<blockquote>
+<p>
+-3- <i>Effects</i>: If <tt>n &lt;= capacity()</tt> is `true`, there are no effects. Otherwise increases 
+`capacity()` by allocating reserved blocks.
+<p/>
+-4- <i>Postconditions</i>: <tt>capacity() &gt;= n</tt> is `true`.
+<p/>
+-5- <i>Throws</i>: `length_error` if <del>`n`</del><ins>`capacity()` cannot be made <tt>&gt;= n</tt> without 
+being</ins> <tt>&gt; max_size()</tt>, as well as any exceptions thrown by the allocator.
+<p/>
+[&hellip;]
+</p>
+</blockquote>
+</blockquote>
+
+</li>
+
+</ol>
+</resolution>
+
+</issue>