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New issue from Jiang An: "Inconsistent preconditions for transparent …
…insertion of std::flat_map/std::flat_set"
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| <?xml version='1.0' encoding='utf-8' standalone='no'?> | ||
| <!DOCTYPE issue SYSTEM "lwg-issue.dtd"> | ||
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| <issue num="4048" status="New"> | ||
| <title>Inconsistent preconditions for transparent insertion of <tt>std::flat_map/std::flat_set</tt></title> | ||
| <section><sref ref="[flat.set]"/><sref ref="[flat.map.overview]"/></section> | ||
| <submitter>Jiang An</submitter> | ||
| <date>26 Jan 2024</date> | ||
| <priority>99</priority> | ||
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| <discussion> | ||
| <p> | ||
| The preconditions for transparent insertion of associative containers (<sref ref="[map.modifiers]"/>/13, | ||
| <sref ref="[map.modifiers]"/>/29, and <sref ref="[set.modifiers]"/>/3) detect the results of <tt>equal_range</tt>, | ||
| while those for <tt>std::flat_set</tt> and <tt>std::flat_map</tt> (<sref ref="[flat.set.modifiers]"/>/2 and | ||
| <sref ref="[flat.map.modifiers]"/>/20) currently detect the results of <tt>find</tt>, which is inconsistent. | ||
| <p/> | ||
| During implementing <tt>std::flat_set</tt> in MSVC STL, it was reported | ||
| (<a href="https://github.com/microsoft/STL/issues/4105">microsoft/STL#4105</a>) that the current preconditions | ||
| for <tt>std::flat_set::insert</tt> can lead to inconsistent results. Tim Song told that the current preconditions | ||
| were copied from old revisions of <paper num="P2363"/>. So, presumably we should change these preconditions for | ||
| flat container adaptors to consistently use <tt>equal_range</tt>. | ||
| </p> | ||
| </discussion> | ||
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| <resolution> | ||
| <p> | ||
| This wording is relative to <paper num="N4971"/>. | ||
| </p> | ||
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| <ol> | ||
| <li><p>Modify <sref ref="[flat.map.modifiers]"/> as indicated:</p> | ||
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| <blockquote> | ||
| <pre> | ||
| template<class K, class... Args> | ||
| pair<iterator, bool> try_emplace(K&& k, Args&&... args); | ||
| template<class K, class... Args> | ||
| iterator try_emplace(const_iterator hint, K&& k, Args&&... args); | ||
| </pre> | ||
| <blockquote> | ||
| <p> | ||
| […] | ||
| <p/> | ||
| -20- <i>Preconditions</i>: The conversion from <tt>k</tt> into <tt>key_type</tt> constructs an | ||
| object <tt>u</tt>, for which <tt><del>find(k) == find(u)</del><ins>equal_range(k) == equal_range(u)</ins></tt> | ||
| is <tt>true</tt>. | ||
| </p> | ||
| </blockquote> | ||
| </blockquote> | ||
| </li> | ||
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| <li><p>Modify <sref ref="[flat.set.modifiers]"/> as indicated:</p> | ||
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| <blockquote> | ||
| <pre> | ||
| template<class K> pair<iterator, bool> insert(K&& x); | ||
| template<class K> iterator insert(const_iterator hint, K&& x); | ||
| </pre> | ||
| <blockquote> | ||
| <p> | ||
| […] | ||
| <p/> | ||
| -2- <i>Preconditions</i>: The conversion from <tt>x</tt> into <tt>value_type</tt> constructs an | ||
| object <tt>u</tt>, for which <tt><del>find(x) == find(u)</del><ins>equal_range(x) == equal_range(u)</ins></tt> | ||
| is <tt>true</tt>. | ||
| </p> | ||
| </blockquote> | ||
| </blockquote> | ||
| </li> | ||
| </ol> | ||
| </resolution> | ||
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| </issue> |