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LWG4272: New proposed resolution fixing constructor from padded layouts
This fixes mistake pointed out on reflector.
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‎xml/issue4272.xml‎

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@@ -250,9 +250,8 @@ template<class OtherExtents>
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</superseded>
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<note>2025-06-20, Luc Grosheintz provides further wording improvements</note>
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</discussion>
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<resolution>
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<superseded>
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<p>
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This wording is relative to <paper num="N5008"/>.
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</p>
@@ -493,7 +492,255 @@ LayoutRightPaddedMapping::padding_value == dynamic_extent)
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</blockquote>
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</li>
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</ol>
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</superseded>
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<note>2025-09-27, Tomasz Kamiński fixes constraints in constructors from padded layouts</note>
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</discussion>
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<resolution>
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<p>
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This wording is relative to <paper num="N5008"/>.
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</p>
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<blockquote class="note">
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<p>
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[<i>Drafting note</i>: As drive-by fixes the edits for <tt>layout_left_padded&lt;&gt;::mapping</tt> and
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<tt>layout_right_padded&lt;&gt;::mapping</tt> also correct an editorial asymmetry between class
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header synopsis declaration form and prototype specification form of the corresponding
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constructors and adjust to the correct formatting of the exposition-only data member <tt><i>rank_</i></tt>.]
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</p>
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</blockquote>
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<ol>
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<li><p>Modify <sref ref="[mdspan.layout.left.overview]"/> 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;class Extents&gt;
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class layout_left::mapping {
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[&hellip;]
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<i>// <sref ref="[mdspan.layout.left.cons]"/>, constructors</i>
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[&hellip;]
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template&lt;class OtherExtents&gt;
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constexpr explicit(<del>extents_type::rank() &gt; 0</del><ins><i>see below</i></ins>)
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mapping(const layout_stride::mapping&lt;OtherExtents&gt;&amp;);
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constexpr mapping&amp; operator=(const mapping&amp;) noexcept = default;
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[&hellip;]
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};
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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 <sref ref="[mdspan.layout.left.cons]"/> as indicated:</p>
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<blockquote>
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<pre>
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template&lt;class OtherExtents&gt;
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constexpr explicit(<del>extents_type::rank() &gt; 0</del><ins><i>see below</i></ins>)
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mapping(const layout_stride::mapping&lt;OtherExtents&gt;&amp; other);
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</pre>
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<blockquote>
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<p>
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-13- <i>Constraints</i>: [&hellip;]
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<p/>
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-14- <i>Preconditions</i>: [&hellip;]
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<p/>
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-15- <i>Effects</i>: [&hellip;]
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<p/>
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<ins>-?- <i>Remarks</i>: The expression inside `explicit` is equivalent to:</ins>
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</p>
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<blockquote><pre>
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<ins>!(extents_type::rank() == 0 &amp;&amp; is_convertible_v&lt;OtherExtents, extents_type&gt;)</ins>
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</pre></blockquote>
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</blockquote>
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</blockquote>
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</li>
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<li><p>Modify <sref ref="[mdspan.layout.right.overview]"/> 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;class Extents&gt;
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class layout_right::mapping {
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[&hellip;]
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<i>// <sref ref="[mdspan.layout.right.cons]"/>, constructors</i>
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[&hellip;]
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template&lt;class OtherExtents&gt;
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constexpr explicit(<del>extents_type::rank() &gt; 0</del><ins><i>see below</i></ins>)
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mapping(const layout_stride::mapping&lt;OtherExtents&gt;&amp;);
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constexpr mapping&amp; operator=(const mapping&amp;) noexcept = default;
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[&hellip;]
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};
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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 <sref ref="[mdspan.layout.right.cons]"/> as indicated:</p>
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<blockquote>
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<pre>
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template&lt;class OtherExtents&gt;
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constexpr explicit(<del>extents_type::rank() &gt; 0</del><ins><i>see below</i></ins>)
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mapping(const layout_stride::mapping&lt;OtherExtents&gt;&amp; other);
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</pre>
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<blockquote>
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<p>
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-13- <i>Constraints</i>: [&hellip;]
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<p/>
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-14- <i>Preconditions</i>: [&hellip;]
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<p/>
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-15- <i>Effects</i>: [&hellip;]
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<p/>
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<ins>-?- <i>Remarks</i>: The expression inside `explicit` is equivalent to:</ins>
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</p>
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<blockquote><pre>
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<ins>!(extents_type::rank() == 0 &amp;&amp; is_convertible_v&lt;OtherExtents, extents_type&gt;)</ins>
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</pre></blockquote>
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</blockquote>
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</blockquote>
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</li>
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<li><p>Modify <sref ref="[mdspan.layout.leftpad.overview]"/> 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;size_t PaddingValue&gt;
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template&lt;class Extents&gt;
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class layout_left_padded&lt;PaddingValue&gt;::mapping {
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[&hellip;]
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<i>// <sref ref="[mdspan.layout.leftpad.cons]"/>, constructors</i>
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[&hellip;]
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template&lt;class OtherExtents&gt;
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constexpr explicit(<del>extents_type::rank() &gt; 0</del><ins><i>see below</i></ins>)
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mapping(const layout_stride::mapping&lt;OtherExtents&gt;&amp;);
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[&hellip;]
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};
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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 <sref ref="[mdspan.layout.leftpad.cons]"/> as indicated:</p>
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<blockquote>
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<pre>
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template&lt;class OtherExtents&gt;
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constexpr explicit(<del>rank_ &gt; 0</del><ins><i>see below</i></ins>)
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mapping(const layout_stride::mapping&lt;OtherExtents&gt;&amp; other);
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</pre>
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<blockquote>
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<p>
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-10- <i>Constraints</i>: [&hellip;]
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<p/>
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-11- <i>Preconditions</i>: [&hellip;]
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<p/>
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-12- <i>Effects</i>: [&hellip;]
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<p/>
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<ins>-?- <i>Remarks</i>: The expression inside `explicit` is equivalent to:</ins>
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</p>
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<blockquote><pre>
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<ins>!(<i>rank_</i> == 0 &amp;&amp; is_convertible_v&lt;OtherExtents, extents_type&gt;)</ins>
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</pre></blockquote>
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</blockquote>
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<pre>
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template&lt;class LayoutLeftPaddedMapping&gt;
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constexpr explicit(<i>see below</i>)
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mapping(const LayoutLeftPaddedMapping&amp; other);
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</pre>
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<blockquote>
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<p>
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-13- <i>Constraints</i>: [&hellip;]
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<p/>
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[&hellip;]
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<p/>
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-16- <i>Remarks</i>: The expression inside `explicit` is equivalent to:
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</p>
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<blockquote><pre>
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<ins>!is_convertible_v&lt;typename LayoutLeftPaddedMapping::extents_type, extents_type&gt; ||</ins>
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rank_&gt; 1 &amp;&amp;
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(padding_value != dynamic_extent ||
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LayoutLeftPaddedMapping::padding_value == dynamic_extent)
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</pre></blockquote>
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</blockquote>
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</blockquote>
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</li>
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<li><p>Modify <sref ref="[mdspan.layout.rightpad.overview]"/> 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;size_t PaddingValue&gt;
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template&lt;class Extents&gt;
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class layout_right_padded&lt;PaddingValue&gt;::mapping {
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[&hellip;]
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<i>// <sref ref="[mdspan.layout.rightpad.cons]"/>, constructors</i>
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[&hellip;]
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template&lt;class OtherExtents&gt;
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constexpr explicit(<del>rank_ &gt; 0</del><ins><i>see below</i></ins>)
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mapping(const layout_stride::mapping&lt;OtherExtents&gt;&amp;);
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[&hellip;]
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};
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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 <sref ref="[mdspan.layout.rightpad.cons]"/> as indicated:</p>
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<blockquote>
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<pre>
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template&lt;class OtherExtents&gt;
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constexpr explicit(<del>rank_ &gt; 0</del><ins><i>see below</i></ins>)
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mapping(const layout_stride::mapping&lt;OtherExtents&gt;&amp; other);
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</pre>
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<blockquote>
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<p>
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-10- <i>Constraints</i>: [&hellip;]
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<p/>
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-11- <i>Preconditions</i>: [&hellip;]
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<p/>
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-12- <i>Effects</i>: [&hellip;]
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<p/>
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<ins>-?- <i>Remarks</i>: The expression inside `explicit` is equivalent to:</ins>
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</p>
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<blockquote><pre>
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<ins>!(<i>rank_</i> == 0 &amp;&amp; is_convertible_v&lt;OtherExtents, extents_type&gt;)</ins>
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</pre></blockquote>
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</blockquote>
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<pre>
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template&lt;class LayoutRightPaddedMapping&gt;
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constexpr explicit(<i>see below</i>)
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mapping(const LayoutRightPaddedMapping&amp; other);
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</pre>
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<blockquote>
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<p>
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-13- <i>Constraints</i>: [&hellip;]
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<p/>
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[&hellip;]
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<p/>
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-17- <i>Remarks</i>: The expression inside `explicit` is equivalent to:
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</p>
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<blockquote><pre>
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<ins>!is_convertible_v&lt;typename LayoutRightPaddedMapping::extents_type, extents_type&gt; ||</ins>
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<i>rank_</i> &gt; 1 &amp;&amp;
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(padding_value != dynamic_extent ||
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LayoutRightPaddedMapping::padding_value == dynamic_extent)
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</pre></blockquote>
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</blockquote>
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</blockquote>
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</li>
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</ol>
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</resolution>
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</issue>

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