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<title>Issue 4053: Unary call to std::views::repeat does not decay the argument</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#WP">WP</a> status.</em></p>
<h3 id="4053"><a href="lwg-defects.html#4053">4053</a>. Unary call to <code>std::views::repeat</code> does not decay the argument</h3>
<p><b>Section:</b> 25.6.5.2 <a href="https://wg21.link/range.repeat.view">[range.repeat.view]</a> <b>Status:</b> <a href="lwg-active.html#WP">WP</a>
 <b>Submitter:</b> Jiang An <b>Opened:</b> 2024-02-05 <b>Last modified:</b> 2024-04-02</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#range.repeat.view">issues</a> in [range.repeat.view].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#WP">WP</a> status.</p>
<p><b>Discussion:</b></p>
<p>
Currently, a binary call to <code>std::views::repeat</code> decay the arguments due to the deduction guide, 
but a unary call doesn't, which is inconsistent.
<p/>
For example:
</p>
<blockquote><pre>
#include &lt;concepts&gt;
#include &lt;ranges&gt;

using RPV = std::ranges::repeat_view&lt;const char*&gt;;

static_assert(std::same_as&lt;decltype(std::views::repeat("foo", std::unreachable_sentinel)), RPV&gt;); // OK
static_assert(std::same_as&lt;decltype(std::views::repeat(+"foo", std::unreachable_sentinel)), RPV&gt;); // OK
static_assert(std::same_as&lt;decltype(std::views::repeat("foo")), RPV&gt;); // <span style="color:red;font-weight:bolder">ill-formed</span>
static_assert(std::same_as&lt;decltype(std::views::repeat(+"foo")), RPV&gt;); // OK
</pre></blockquote>
<p>
Presumably we should extend the deduction guide of <code>std::ranges::repeat_view</code> to cover the unary cases.
</p>

<p><i>[2024-03-12; Reflector poll]</i></p>

<p>
Set status to Tentatively Ready after six votes in favour during reflector poll.
</p>

<p><i>[Tokyo 2024-03-23; Status changed: Voting &rarr; WP.]</i></p>



<p id="res-4053"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N4971" title=" Working Draft, Programming Languages — C++">N4971</a>.
</p>

<ol>
<li><p>Modify 25.6.5.2 <a href="https://wg21.link/range.repeat.view">[range.repeat.view]</a>, class template <code>repeat_view</code> synopsis, as indicated:</p>

<blockquote class="note">
<p>
[<i>Drafting note:</i> The proposed wording has been suggested by Casey Carter, see 
<a href="https://github.com/microsoft/STL/issues/3576">microsoft/STL#3576</a>]
</p>
</blockquote>

<blockquote>
<pre>
namespace std::ranges {
  [&hellip;]

  template&lt;class T, class Bound <ins>= unreachable_sentinel_t</ins>&gt;
    repeat_view(T, Bound <ins>= Bound()</ins>) -&gt; repeat_view&lt;T, Bound&gt;;
}
</pre>
</blockquote>
</li>
</ol>





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