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<!DOCTYPE html>
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<title>Issue 4245: Operators that interact with counted_iterator and default_sentinel_t should be noexcept</title>
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<meta property="og:title" content="Issue 4245: Operators that interact with counted_iterator and default_sentinel_t should be noexcept">
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<meta property="og:description" content="C++ library issue. Status: New">
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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#New">New</a> status.</em></p>
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<h3 id="4245"><a href="lwg-active.html#4245">4245</a>. Operators that interact with <code class='backtick'>counted_iterator</code> and <code class='backtick'>default_sentinel_t</code> should be <code class='backtick'>noexcept</code></h3>
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<p><b>Section:</b> 24.5.7.1 <a href="https://wg21.link/counted.iterator">[counted.iterator]</a>, 24.5.7.5 <a href="https://wg21.link/counted.iter.nav">[counted.iter.nav]</a>, 24.5.7.6 <a href="https://wg21.link/counted.iter.cmp">[counted.iter.cmp]</a> <b>Status:</b> <a href="lwg-active.html#New">New</a>
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<b>Submitter:</b> Hewill Kang <b>Opened:</b> 2025-04-18 <b>Last modified:</b> 2025-04-21</p>
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<p><b>Priority: </b>Not Prioritized
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</p>
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<p><b>View all other</b> <a href="lwg-index.html#counted.iterator">issues</a> in [counted.iterator].</p>
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<p><b>View all issues with</b> <a href="lwg-status.html#New">New</a> status.</p>
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<p><b>Discussion:</b></p>
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<p>
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<code class='backtick'>counted_iterator</code> can be compared or subtracted from <code class='backtick'>default_sentinel_t</code>,
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which only involves simple integer arithmetic and does not have any <i>Preconditions</i>.
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<p/>
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In this case, it is reasonable to declare them as <code>noexcept</code>.
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</p>
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<p id="res-4245"><b>Proposed resolution:</b></p>
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<p>
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This wording is relative to <a href="https://wg21.link/N5008">N5008</a>.
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</p>
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<ol>
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<li><p>Modify 24.5.7.1 <a href="https://wg21.link/counted.iterator">[counted.iterator]</a> as indicated:</p>
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<blockquote>
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<pre>
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namespace std {
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template&lt;input_or_output_iterator I&gt;
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class counted_iterator {
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public:
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[&hellip;]
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friend constexpr iter_difference_t&lt;I&gt; operator-(
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const counted_iterator&amp; x, default_sentinel_t) <ins>noexcept</ins>;
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friend constexpr iter_difference_t&lt;I&gt; operator-(
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default_sentinel_t, const counted_iterator&amp; y) <ins>noexcept</ins>;
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[&hellip;]
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friend constexpr bool operator==(
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const counted_iterator&amp; x, default_sentinel_t) <ins>noexcept</ins>;
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[&hellip;]
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};
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[&hellip;]
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}
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</pre>
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</blockquote>
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</li>
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<li><p>Modify 24.5.7.5 <a href="https://wg21.link/counted.iter.nav">[counted.iter.nav]</a> as indicated:</p>
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<blockquote>
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<pre>
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friend constexpr iter_difference_t&lt;I&gt; operator-(
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const counted_iterator&amp; x, default_sentinel_t) <ins>noexcept</ins>;
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</pre>
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<blockquote>
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<p>
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-15- <i>Effects</i>: Equivalent to: <code>return -x.length;</code>
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</p>
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</blockquote>
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<pre>
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friend constexpr iter_difference_t&lt;I&gt; operator-(
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default_sentinel_t, const counted_iterator&amp; y) <ins>noexcept</ins>;
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</pre>
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<blockquote>
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<p>
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-16- <i>Effects</i>: Equivalent to: <code>return y.length;</code>
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</p>
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</blockquote>
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</blockquote>
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</li>
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<li><p>Modify 24.5.7.6 <a href="https://wg21.link/counted.iter.cmp">[counted.iter.cmp]</a> as indicated:</p>
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<blockquote>
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<pre>
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friend constexpr bool operator==(
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const counted_iterator&amp; x, default_sentinel_t) <ins>noexcept</ins>;
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</pre>
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<blockquote>
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<p>
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-3- <i>Effects</i>: Equivalent to: <code>return x.length == 0;</code>
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</p>
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</blockquote>
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</blockquote>
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</li>
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</ol>
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</body>
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</html>

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