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<title>Issue 3226: zoned_time constructor from string_view should accept
zoned_time&lt;Duration2, TimeZonePtr2&gt;</title>
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zoned_time&lt;Duration2, TimeZonePtr2&gt;">
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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="3226"><a href="lwg-defects.html#3226">3226</a>. <code>zoned_time</code> constructor from <code>string_view</code> should accept
<code>zoned_time&lt;Duration2, TimeZonePtr2&gt;</code></h3>
<p><b>Section:</b> 30.11.7.2 <a href="https://wg21.link/time.zone.zonedtime.ctor">[time.zone.zonedtime.ctor]</a> <b>Status:</b> <a href="lwg-active.html#C++20">C++20</a>
 <b>Submitter:</b> Tomasz Kami&nacute;ski <b>Opened:</b> 2019-06-23 <b>Last modified:</b> 2021-02-25</p>
<p><b>Priority: </b>2
</p>
<p><b>View all other</b> <a href="lwg-index.html#time.zone.zonedtime.ctor">issues</a> in [time.zone.zonedtime.ctor].</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>
<code>zoned_time</code> constructors with <code>string_view</code> and
another <code>zoned_time</code> are not accepting <code>zoned_time</code>
instances that use a different time zone representation (<code>TimeZonePtr</code> parameter):
</p>
<blockquote><pre>
zoned_time(string_view name, const zoned_time&lt;Duration&gt;&amp; zt);
zoned_time(string_view name, const zoned_time&lt;Duration&gt;&amp; zt, choose);
</pre></blockquote>
<p>
This makes them inconsistent with the constructors from <code>TimeZonePtr</code> 
and <code>zoned_time</code>, that they delegate to: 
</p>
<blockquote><pre>
template&lt;class Duration2, class TimeZonePtr2&gt;
  zoned_time(TimeZonePtr z, const zoned_time&lt;Duration2, TimeZonePtr2&gt;&amp; zt);
template&lt;class Duration2, class TimeZonePtr2&gt;
  zoned_time(TimeZonePtr z, const zoned_time&lt;Duration2, TimeZonePtr2&gt;&amp; zt, choose);
</pre></blockquote>
<p>
Furthermore it forces the creation of a temporary <code>zoned_time</code> object in 
case when the source uses the same <code>TimeZonePtr</code>, but different <code>Duration</code>.
</p>

<strong>Previous resolution [SUPERSEDED]:</strong>
<blockquote class="note">
<p>This wording is relative to <a href="https://wg21.link/n4820">N4820</a>.</p>

<ol>
<li><p>Modify 30.11.7.1 <a href="https://wg21.link/time.zone.zonedtime.overview">[time.zone.zonedtime.overview]</a>, class template <code>zoned_time</code> synopsis, 
as indicated:</p>

<blockquote>
<pre>
<ins>template&lt;class Duration2, class TimeZonePtr2&gt;</ins>
zoned_time(string_view name, const zoned_time&lt;Duration<ins>2, TimeZonePtr2</ins>&gt;&amp; zt);
<ins>template&lt;class Duration2, class TimeZonePtr2&gt;</ins>
zoned_time(string_view name, const zoned_time&lt;Duration<ins>2, TimeZonePtr2</ins>&gt;&amp; zt, choose);</pre>
</blockquote>
</li>

<li><p>Modify 30.11.7.2 <a href="https://wg21.link/time.zone.zonedtime.ctor">[time.zone.zonedtime.ctor]</a> as indicated:</p>

<blockquote>
<pre>
<ins>template&lt;class Duration2, class TimeZonePtr2&gt;</ins>
zoned_time(string_view name, const zoned_time&lt;Duration<ins>2, TimeZonePtr2</ins>&gt;&amp; y);
</pre>
<blockquote>
<p>
-32- <i>Remarks:</i> This constructor does not participate in overload resolution unless 
<code>zoned_time</code> is constructible from the return type of <code>traits::locate_zone(name)</code> 
and <code>zoned_time<ins>&lt;Duration2, TimeZonePtr2&gt;</ins></code>.
<p/>
-33- <i>Effects:</i> Equivalent to construction with <code>{traits::locate_zone(name), y}</code>.
</p>
</blockquote>
<pre>
<ins>template&lt;class Duration2, class TimeZonePtr2&gt;</ins>
zoned_time(string_view name, const zoned_time&lt;Duration<ins>2, TimeZonePtr2</ins>&gt;&amp; y, choose c););
</pre>
<blockquote>
<p>
-34- <i>Remarks:</i> This constructor does not participate in overload resolution unless 
<code>zoned_time</code> is constructible from the return type of <code>traits::locate_zone(name)</code>, 
<code>zoned_time<ins>&lt;Duration2, TimeZonePtr2&gt;</ins></code>, and <code>choose</code>.
<p/>
-35- <i>Effects:</i> Equivalent to construction with <code>{traits::locate_zone(name), y, c}</code>.
<p/>
-36- [<i>Note:</i> The <code>choose</code> parameter has no effect. &mdash; <i>end note</i>]
</p>
</blockquote>
</blockquote>
</li>
</ol>

</blockquote>

<p><i>[2020-02-13, Prague]</i></p>

<p>
During LWG discussions it was suggested to rebase the wording to reduce the chances for confusion.
</p>
<p><i>[2020-02 Status to Immediate on Thursday morning in Prague.]</i></p>



<p id="res-3226"><b>Proposed resolution:</b></p>
<p>This wording is relative to <a href="https://wg21.link/n4849">N4849</a>.</p>

<ol>
<li><p>Modify 30.11.7.1 <a href="https://wg21.link/time.zone.zonedtime.overview">[time.zone.zonedtime.overview]</a>, class template <code>zoned_time</code> synopsis, 
as indicated:</p>

<blockquote>
<pre>
<ins>template&lt;class Duration2, class TimeZonePtr2&gt;</ins>
zoned_time(string_view name, const zoned_time&lt;Duration<ins>2, TimeZonePtr2</ins>&gt;&amp; zt);
<ins>template&lt;class Duration2, class TimeZonePtr2&gt;</ins>
zoned_time(string_view name, const zoned_time&lt;Duration<ins>2, TimeZonePtr2</ins>&gt;&amp; zt, choose);</pre>
</blockquote>
</li>

<li><p>Modify 30.11.7.2 <a href="https://wg21.link/time.zone.zonedtime.ctor">[time.zone.zonedtime.ctor]</a> as indicated:</p>

<blockquote>
<pre>
<ins>template&lt;class Duration2, class TimeZonePtr2&gt;</ins>
zoned_time(string_view name, const zoned_time&lt;Duration<ins>2, TimeZonePtr2</ins>&gt;&amp; y);
</pre>
<blockquote>
<p>
-32- <i>Constraints:</i> <code>zoned_time</code> is constructible from the return type of <code>traits::locate_zone(name)</code> 
and <code>zoned_time<ins>&lt;Duration2, TimeZonePtr2&gt;</ins></code>.
<p/>
-33- <i>Effects:</i> Equivalent to construction with <code>{traits::locate_zone(name), y}</code>.
</p>
</blockquote>
<pre>
<ins>template&lt;class Duration2, class TimeZonePtr2&gt;</ins>
zoned_time(string_view name, const zoned_time&lt;Duration<ins>2, TimeZonePtr2</ins>&gt;&amp; y, choose c););
</pre>
<blockquote>
<p>
-34- <i>Constraints:</i> <code>zoned_time</code> is constructible from the return type of <code>traits::locate_zone(name)</code>, 
<code>zoned_time<ins>&lt;Duration2, TimeZonePtr2&gt;</ins></code>, and <code>choose</code>.
<p/>
-35- <i>Effects:</i> Equivalent to construction with <code>{traits::locate_zone(name), y, c}</code>.
<p/>
-36- [<i>Note:</i> The <code>choose</code> parameter has no effect. &mdash; <i>end note</i>]
</p>
</blockquote>
</blockquote>
</li>
</ol>




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