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<title>Issue 3273: Specify weekday_indexed to range of [0, 7]</title>
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<p><em>This page is a snapshot from the LWG issues list, see the <a href="lwg-active.html">Library Active Issues List</a> for more information and the meaning of <a href="lwg-active.html#C++20">C++20</a> status.</em></p>
<h3 id="3273"><a href="lwg-defects.html#3273">3273</a>. Specify <code>weekday_indexed</code> to range of <code>[0, 7]</code></h3>
<p><b>Section:</b> 30.8.7.2 <a href="https://wg21.link/time.cal.wdidx.members">[time.cal.wdidx.members]</a> <b>Status:</b> <a href="lwg-active.html#C++20">C++20</a>
 <b>Submitter:</b> Howard Hinnant <b>Opened:</b> 2019-09-02 <b>Last modified:</b> 2021-02-25</p>
<p><b>Priority: </b>0
</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++20">C++20</a> status.</p>
<p><b>Discussion:</b></p>
<p>
On one hand, we say that if you try to construct a <code>weekday_indexed</code> with index 0, 
you get an unspecified index instead (30.8.7.2 <a href="https://wg21.link/time.cal.wdidx.members">[time.cal.wdidx.members]</a>/p1),:
</p>
<blockquote>
<p>
The values held are unspecified if <code>!wd.ok()</code> or index is not in the range <code>[1, 5]</code>.
</p>
</blockquote>
<p>
OTOH, we take pains to pin down <code>year_month_weekday</code>'s conversion to <code>sys_days</code> 
when the index is zero (30.8.7.2 <a href="https://wg21.link/time.cal.wdidx.members">[time.cal.wdidx.members]</a>/p19):
</p>
<blockquote>
<p>
If <code>index()</code> is <code>0</code> the returned <code>sys_days</code> represents the date <code>7</code> 
days prior to the first <code>weekday()</code> of <code>year()/month()</code>.
</p>
</blockquote>
<p>
This is inconsistent. We should allow a slightly wider range (say, <code>[0, 7]</code>, since you need 
at least 3 bits anyway to represent the 5 distinct valid values, and the <code>0</code> value referred 
to by 30.8.7.2 <a href="https://wg21.link/time.cal.wdidx.members">[time.cal.wdidx.members]</a>/p19.
</p>

<p><i>[2019-09-24 Issue Prioritization]</i></p>

<p>Status to Tentatively Ready and priority to 0 after six positive votes on the reflector.</p>


<p id="res-3273"><b>Proposed resolution:</b></p>
<p>This wording is relative to <a href="https://wg21.link/n4830">N4830</a>.</p>

<ol>
<li><p>Modify 30.8.7.2 <a href="https://wg21.link/time.cal.wdidx.members">[time.cal.wdidx.members]</a> as indicated:</p>

<blockquote class="note">
<p>
[<i>Drafting note:</i> As a drive-by fix a cleanup of "Constructs an object of type <code>weekday_indexed</code>"
wording has been applied as well. ]
</p>
</blockquote>


<blockquote>
<pre>
constexpr weekday_indexed(const chrono::weekday&amp; wd, unsigned index) noexcept;
</pre>
<blockquote>
<p>
-1- <i>Effects:</i> <del>Constructs an object of type <code>weekday_indexed</code> by 
initializing</del><ins>Initializes</ins> <code>wd_</code> with <code>wd</code> and <code>index_</code> with 
<code>index</code>. The values held are unspecified if <code>!wd.ok()</code> or 
<code>index</code> is not in the range <code>[<del>1</del><ins>0</ins>, <del>5</del><ins>7</ins>]</code>.
</p>
</blockquote>
</blockquote>

</li>
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