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<title>Issue 3592: lazy_split_view needs to check the simpleness of Pattern</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++23">C++23</a> status.</em></p>
<h3 id="3592"><a href="lwg-defects.html#3592">3592</a>. <code>lazy_split_view</code> needs to check the simpleness of <code>Pattern</code></h3>
<p><b>Section:</b> 25.7.16.2 <a href="https://wg21.link/range.lazy.split.view">[range.lazy.split.view]</a> <b>Status:</b> <a href="lwg-active.html#C++23">C++23</a>
 <b>Submitter:</b> Tim Song <b>Opened:</b> 2021-09-15 <b>Last modified:</b> 2023-11-22</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View other</b> <a href="lwg-index-open.html#range.lazy.split.view">active issues</a> in [range.lazy.split.view].</p>
<p><b>View all other</b> <a href="lwg-index.html#range.lazy.split.view">issues</a> in [range.lazy.split.view].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++23">C++23</a> status.</p>
<p><b>Discussion:</b></p>
<p>
For forward ranges, the non-<code>const</code> versions of <code>lazy_split_view::begin()</code>
and <code>lazy_split_view::end()</code> returns an <code><i>outer-iterator</i>&lt;<i>simple-view</i>&lt;V&gt;&gt;</code>,
promoting to <code>const</code> if <code>V</code> models <code><i>simple-view</i></code>. However, this failed to
take <code>Pattern</code> into account, even though that will also be accessed as <code>const</code> if 
<code>const</code>-promotion takes place. There is no requirement that <code>const Pattern</code> is a range, 
however.
</p>

<p><i>[2021-09-24; Reflector poll]</i></p>

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

<p><i>[2021-10-14 Approved at October 2021 virtual plenary. Status changed: Voting &rarr; WP.]</i></p>



<p id="res-3592"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/n4892">N4892</a>.
</p>

<ol>
<li><p>Modify 25.7.16.2 <a href="https://wg21.link/range.lazy.split.view">[range.lazy.split.view]</a>, class template <code>lazy_split_view</code> synopsis, as indicated:</p>

<blockquote>
<blockquote>
<pre>
namespace std::ranges {

  [&hellip;]

  template&lt;input_range V, forward_range Pattern&gt;
    requires view&lt;V&gt; &amp;&amp; view&lt;Pattern&gt; &amp;&amp;
             indirectly_comparable&lt;iterator_t&lt;V&gt;, iterator_t&lt;Pattern&gt;, ranges::equal_to&gt; &amp;&amp;
            (forward_range&lt;V&gt; || <i>tiny-range</i>&lt;Pattern&gt;)
  class lazy_split_view : public view_interface&lt;lazy_split_view&lt;V, Pattern&gt;&gt; {
  private:
    [&hellip;]
  public:
    [&hellip;]

    constexpr auto begin() {
      if constexpr (forward_range&lt;V&gt;)
        return <i>outer-iterator</i>&lt;<i>simple-view</i>&lt;V&gt;<ins> &amp;&amp;
          <i>simple-view</i>&lt;Pattern&gt;</ins>&gt;{*this, ranges::begin(<i>base_</i>)};
      else {
        <i>current_</i> = ranges::begin(<i>base_</i>);
        return <i>outer-iterator</i>&lt;false&gt;{*this};
      }
    }
    
    [&hellip;]
    
    constexpr auto end() requires forward_range&lt;V&gt; &amp;&amp; common_range&lt;V&gt; {
      return <i>outer-iterator</i>&lt;<i>simple-view</i>&lt;V&gt;<ins> &amp;&amp;
        <i>simple-view</i>&lt;Pattern&gt;</ins>&gt;{*this, ranges::end(<i>base_</i>)};
    }

    [&hellip;]
  };
  
  [&hellip;]
  
}
</pre>
</blockquote>
</blockquote>
</li>

</ol>





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