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<title>Issue 2778: basic_string_view is missing constexpr</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++17">C++17</a> status.</em></p>
<h3 id="2778"><a href="lwg-defects.html#2778">2778</a>. <code>basic_string_view</code> is missing <code>constexpr</code></h3>
<p><b>Section:</b> 27.3 <a href="https://wg21.link/string.view">[string.view]</a> <b>Status:</b> <a href="lwg-active.html#C++17">C++17</a>
 <b>Submitter:</b> Billy Robert O'Neal III <b>Opened:</b> 2016-09-30 <b>Last modified:</b> 2017-07-30</p>
<p><b>Priority: </b>0
</p>
<p><b>View other</b> <a href="lwg-index-open.html#string.view">active issues</a> in [string.view].</p>
<p><b>View all other</b> <a href="lwg-index.html#string.view">issues</a> in [string.view].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++17">C++17</a> status.</p>
<p><b>Discussion:</b></p>
<p>
<code>basic_string_view</code> was not updated to account for other library
machinery made <code>constexpr</code> in Oulu. Now that <code>reverse_iterator</code> is
<code>constexpr</code> there's no reason the reverse range functions can't be.
Also, now that we have C++14 relaxed <code>constexpr</code>, we can also take care
of the assignment operator and <code>copy</code>.
</p>

<p><i>[Issues processing Telecon 2016-10-7]</i></p>

<p>split off the copy into its' own issue <a href="lwg-defects.html#2780" title="basic_string_view::copy is missing constexpr (Status: Resolved)">2780</a><sup><a href="https://cplusplus.github.io/LWG/issue2780" title="Latest snapshot">(i)</a></sup></p>
<p>P0; set what's left to Tentatively Ready</p>

<p>
<strong>Previous resolution [SUPERSEDED]:</strong>
</p>
<blockquote class="note">
<p>
This wording is relative to N4606.
</p>

<ol>
<li><p>In 27.3.3 <a href="https://wg21.link/string.view.template">[string.view.template]</a>, add <code>constexpr</code> to the assignment operator:</p>

<blockquote>
<pre>
<ins>constexpr </ins>basic_string_view&amp; operator=(const basic_string_view&amp;) noexcept = default;
</pre>
</blockquote>
</li>

<li><p>In 27.3.3 <a href="https://wg21.link/string.view.template">[string.view.template]</a>, add <code>constexpr</code> to the reverse range functions:</p>

<blockquote>
<pre>
<ins>constexpr </ins>const_reverse_iterator rbegin() const noexcept;
<ins>constexpr </ins>const_reverse_iterator rend() const noexcept;
<ins>constexpr </ins>const_reverse_iterator crbegin() const noexcept;
<ins>constexpr </ins>const_reverse_iterator crend() const noexcept;
</pre>
</blockquote>
</li>

<li><p>In 27.3.3.4 <a href="https://wg21.link/string.view.iterators">[string.view.iterators]</a>, add <code>constexpr</code> to the reverse range functions:</p>

<blockquote>
<pre>
<ins>constexpr </ins>const_reverse_iterator rbegin() const noexcept;
<ins>constexpr </ins>const_reverse_iterator crbegin() const noexcept;
</pre>
<blockquote>
<p>
-6- <em>Returns:</em> <code>const_reverse_iterator(end())</code>
</p>
</blockquote>
<pre>
<ins>constexpr </ins>const_reverse_iterator rend() const noexcept;
<ins>constexpr </ins>const_reverse_iterator crend() const noexcept;
</pre>
<blockquote>
<p>
-7- <em>Returns:</em> <code>const_reverse_iterator(begin())</code>
</p>
</blockquote>
</blockquote>
</li>

<li><p>In 27.3.3 <a href="https://wg21.link/string.view.template">[string.view.template]</a>, add <code>constexpr</code> to <code>copy</code>:</p>

<blockquote>
<pre>
<ins>constexpr </ins>size_type copy(charT* s, size_type n, size_type pos = 0) const;
</pre>
</blockquote>
</li>

<li><p>In 27.3.3.8 <a href="https://wg21.link/string.view.ops">[string.view.ops]</a>, add <code>constexpr</code> to <code>copy</code>:</p>

<blockquote>
<pre>
<ins>constexpr </ins>size_type copy(charT* s, size_type n, size_type pos = 0) const;
</pre>
</blockquote>
</li>
</ol>
</blockquote>


<p id="res-2778"><b>Proposed resolution:</b></p>
<p>
This wording is relative to N4606.
</p>

<ol>
<li><p>In 27.3.3 <a href="https://wg21.link/string.view.template">[string.view.template]</a>, add <code>constexpr</code> to the assignment operator:</p>

<blockquote>
<pre>
<ins>constexpr </ins>basic_string_view&amp; operator=(const basic_string_view&amp;) noexcept = default;
</pre>
</blockquote>
</li>

<li><p>In 27.3.3 <a href="https://wg21.link/string.view.template">[string.view.template]</a>, add <code>constexpr</code> to the reverse range functions:</p>

<blockquote>
<pre>
<ins>constexpr </ins>const_reverse_iterator rbegin() const noexcept;
<ins>constexpr </ins>const_reverse_iterator rend() const noexcept;
<ins>constexpr </ins>const_reverse_iterator crbegin() const noexcept;
<ins>constexpr </ins>const_reverse_iterator crend() const noexcept;
</pre>
</blockquote>
</li>

<li><p>In 27.3.3.4 <a href="https://wg21.link/string.view.iterators">[string.view.iterators]</a>, add <code>constexpr</code> to the reverse range functions:</p>

<blockquote>
<pre>
<ins>constexpr </ins>const_reverse_iterator rbegin() const noexcept;
<ins>constexpr </ins>const_reverse_iterator crbegin() const noexcept;
</pre>
<blockquote>
<p>
-6- <em>Returns:</em> <code>const_reverse_iterator(end())</code>
</p>
</blockquote>
<pre>
<ins>constexpr </ins>const_reverse_iterator rend() const noexcept;
<ins>constexpr </ins>const_reverse_iterator crend() const noexcept;
</pre>
<blockquote>
<p>
-7- <em>Returns:</em> <code>const_reverse_iterator(begin())</code>
</p>
</blockquote>
</blockquote>
</li>

</ol>






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