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<title>Issue 2938: basic_string_view::const_iterator should be literal types</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#Resolved">Resolved</a> status.</em></p>
<h3 id="2938"><a href="lwg-defects.html#2938">2938</a>. <code>basic_string_view::const_iterator</code> should be literal types</h3>
<p><b>Section:</b> 27.3.3 <a href="https://wg21.link/string.view.template">[string.view.template]</a> <b>Status:</b> <a href="lwg-active.html#Resolved">Resolved</a>
 <b>Submitter:</b> Antony Polukhin <b>Opened:</b> 2017-03-01 <b>Last modified:</b> 2020-09-06</p>
<p><b>Priority: </b>2
</p>
<p><b>View all other</b> <a href="lwg-index.html#string.view.template">issues</a> in [string.view.template].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#Resolved">Resolved</a> status.</p>
<p><b>Discussion:</b></p>
<p>
Force the literal type requirement for the <code>const_iterator</code> in the
<code>std::basic_string_view</code> so that iterators of <code>std::basic_string_view</code>
could be used in <code>constexpr</code> functions.
</p>

<p><i>[2017-03-02, Kona]</i></p>

<p>
Wording tweaks suggested by LWG applied.
</p>

<p><i>[2017-03-02, Tim Song comments]</i></p>

<p>
I don't believe the blanket "all operations" wording is quite correct.
<p/>
First, <code>T t;</code> (required by <code>DefaultConstructible</code>) isn't usable in a constant expression if the iterator is a 
pointer, since it would leave it uninitialized. 
<p/>
Second, an explicit destructor call <code>u.~T()</code> (required by <code>Destructible</code>) isn't usable if the iterator is a 
class type because it explicitly invokes a non-<code>constexpr</code> function (the destructor); see [expr.const]/2.2.
</p>

<p><i>[2017-03-04, Kona]</i></p>

<p>Set priority to 2. Lisa and Alisdair to work with Antony to come up with better wording. The same wording can be used for <a href="lwg-defects.html#2897" title="array::iterator and array::const_iterator should be literal types (Status: Resolved)">2897</a><sup><a href="https://cplusplus.github.io/LWG/issue2897" title="Latest snapshot">(i)</a></sup>.</p>

<p><i>[2017-11 Albuquerque Saturday issues processing]</i></p>

<p><a href="https://wg21.link/P0858R0">P0858R0</a> (adopted on Sat; to be moved in Jacksonville) will resolve this.</p>

<p><i>[2018-06 Rapperswil Wednesday issues processing]</i></p>

<p>This was resolved by <a href="https://wg21.link/P0858">P0858</a>, which was adopted in Jacksonville.</p>


<p id="res-2938"><b>Proposed resolution:</b></p>
<p>This wording is relative to <a href="https://wg21.link/n4640">N4640</a>.</p>

<ol>
<li><p>Add to the end of the 27.3.3 <a href="https://wg21.link/string.view.template">[string.view.template]</a> section:</p>

<blockquote>
<p>
-1- In every specialization <code>basic_string_view&lt;charT, traits&gt;</code>, the type traits shall satisfy the character
traits requirements (21.2), and the type <code>traits::char_type</code> shall name the same type as <code>charT</code>.
<p/>
<ins>-?- All operations on <code>iterator</code> and <code>const_iterator</code> that are required to satisfy the 
random access iterator requirements are usable in constant expressions.</ins>
</p>
</blockquote>

</li>
</ol>







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