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<title>Issue 2193: Default constructors for standard library containers are explicit</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++14">C++14</a> status.</em></p>
<h3 id="2193"><a href="lwg-defects.html#2193">2193</a>. Default constructors for standard library containers are explicit</h3>
<p><b>Section:</b> 23 <a href="https://wg21.link/containers">[containers]</a> <b>Status:</b> <a href="lwg-active.html#C++14">C++14</a>
 <b>Submitter:</b> Richard Smith <b>Opened:</b> 2012-10-04 <b>Last modified:</b> 2017-07-05</p>
<p><b>Priority: </b>1
</p>
<p><b>View other</b> <a href="lwg-index-open.html#containers">active issues</a> in [containers].</p>
<p><b>View all other</b> <a href="lwg-index.html#containers">issues</a> in [containers].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++14">C++14</a> status.</p>
<p><b>Discussion:</b></p>

<p>
Most (all?) of the standard library containers have explicit default constructors. Consequently:
</p>
<blockquote><pre>
std::set&lt;int&gt; s1 = { 1, 2 }; // ok
std::set&lt;int&gt; s2 = { 1 }; // ok
std::set&lt;int&gt; s3 = {}; // ill-formed, copy-list-initialization selected an explicit constructor
</pre></blockquote>
<p>
Note that Clang + libc++ rejects the declaration of <code>s3</code> for this reason. This cannot possibly match the intent.
</p>
<p>
Suggested fix: apply this transformation throughout the standard library:
</p>
<blockquote><pre>
<ins>set() : set(Compare()) {}</ins>
explicit set(const Compare&amp; comp<del> = Compare()</del>,
             const Allocator&amp; = Allocator());
</pre></blockquote>

<p><i>[
2012-10-06: Daniel adds concrete wording.
]</i></p>


<p><i>[2012, Portland: Move to Open]</i></p>

<p>
This may be an issue better solved by a core language tweak.  Throw the issue over to EWG and see whether they
believe the issue is better resolved in Core or Library.
</p>

<p>
AJM suggest we spawn a new status of 'EWG' to handle such issues - and will move this issue appropriately when
the software can record such resolutions.
</p>

<p><i>[2013-08-27, Joaqu&iacute;n M L&oacute;pez Mu&ntilde;oz comments:]</i></p>


<p>
For the record, I'd like to point out that the resolution proposed by the submitter, namely replacing
</p>

<blockquote><pre>
explicit basic_string(const Allocator&amp; a = Allocator());
</pre></blockquote>

<p>
by
</p>

<blockquote><pre>
basic_string() : basic_string(Allocator()) {}
explicit basic_string(const Allocator&amp; a);
</pre></blockquote>

<p>
(and similarly for other container and container-like classes) might introduce a potential
backwards-compatibility problem related with explicit instantiation. Consider for instance
</p>

<blockquote><pre>
struct my_allocator
{
  my_allocator(...); // no default ctor
  ...
};

template class std::basic_string&lt;char, std::char_traits&lt;char&gt;, my_allocator&lt;char&gt;&gt;;
</pre></blockquote>

<p>
This (which I understand is currently a valid explicit instantiation of <code>std::basic_string</code>) will break if
<code>std::basic_string</code> ctors are modified as proposed by this issue, since <code>my_allocator</code> doesn't have
a default ctor.
</p>

<p><i>[2013-10-06, Daniel comments:]</i></p>


<p>
Issue <a href="lwg-active.html#2303" title="Explicit instantiation of std::vector&lt;UserType&gt; broken? (Status: New)">2303</a><sup><a href="https://cplusplus.github.io/LWG/issue2303" title="Latest snapshot">(i)</a></sup> describes the more general problem related to explicit instantiation requests in the current
library and may help to solve this problem here as well.
</p>

<p><i>[2014-02-13, Issaquah, Jonathan revises wording]</i></p>


<p><strong>Previous resolution from Daniel [SUPERSEDED]:</strong></p>

<blockquote class="note">

<p>This wording is relative to N3376.</p>

<p>The more general criterion for performing the suggested transformation was: Any type with an initializer-list 
constructor that also has an explicit default constructor.</p>

<ol>
<li><p>Change class template <code>basic_string</code> synopsis, 27.4.3 <a href="https://wg21.link/basic.string">[basic.string]</a> p5 as indicated:</p>
<blockquote><pre>
<ins>basic_string() : basic_string(Allocator()) {}</ins>
explicit basic_string(const Allocator&amp; a<del> = Allocator()</del>);
</pre></blockquote>
</li>

<li><p>Change 27.4.3.3 <a href="https://wg21.link/string.cons">[string.cons]</a> before p1 as indicated:</p>
<blockquote><pre>
explicit basic_string(const Allocator&amp; a<del> = Allocator()</del>);
</pre></blockquote>
</li>

<li><p>Change class template <code>deque</code> synopsis, 23.3.5.1 <a href="https://wg21.link/deque.overview">[deque.overview]</a> p2 as indicated:</p>
<blockquote><pre>
<ins>deque() : deque(Allocator()) {}</ins>
explicit deque(const Allocator&amp;<del> = Allocator()</del>);
</pre></blockquote>
</li>

<li><p>Change 23.3.5.2 <a href="https://wg21.link/deque.cons">[deque.cons]</a> before p1 as indicated:</p>
<blockquote><pre>
explicit deque(const Allocator&amp;<del> = Allocator()</del>);
</pre></blockquote>
</li>

<li><p>Change class template <code>forward_list</code> synopsis,  [forwardlist.overview] p3 as indicated:</p>
<blockquote><pre>
<ins>forward_list() : forward_list(Allocator()) {}</ins>
explicit forward_list(const Allocator&amp;<del> = Allocator()</del>);
</pre></blockquote>
</li>

<li><p>Change  [forwardlist.cons] before p1 as indicated:</p>
<blockquote><pre>
explicit forward_list(const Allocator&amp;<del> = Allocator()</del>);
</pre></blockquote>
</li>

<li><p>Change class template <code>list</code> synopsis, 23.3.11.1 <a href="https://wg21.link/list.overview">[list.overview]</a> p2 as indicated:</p>
<blockquote><pre>
<ins>list() : list(Allocator()) {}</ins>
explicit list(const Allocator&amp;<del> = Allocator()</del>);
</pre></blockquote>
</li>

<li><p>Change 23.3.11.2 <a href="https://wg21.link/list.cons">[list.cons]</a> before p1 as indicated:</p>
<blockquote><pre>
explicit list(const Allocator&amp;<del> = Allocator()</del>);
</pre></blockquote>
</li>

<li><p>Change class template <code>vector</code> synopsis, 23.3.13.1 <a href="https://wg21.link/vector.overview">[vector.overview]</a> p2 as indicated:</p>
<blockquote><pre>
<ins>vector() : vector(Allocator()) {}</ins>
explicit vector(const Allocator&amp;<del> = Allocator()</del>);
</pre></blockquote>
</li>

<li><p>Change 23.3.13.2 <a href="https://wg21.link/vector.cons">[vector.cons]</a> before p1 as indicated:</p>
<blockquote><pre>
explicit vector(const Allocator&amp;<del> = Allocator()</del>);
</pre></blockquote>
</li>

<li><p>Change class template specialization <code>vector&lt;bool&gt;</code> synopsis, 23.3.14 <a href="https://wg21.link/vector.bool">[vector.bool]</a> p1 as indicated:</p>
<blockquote><pre>
<ins>vector() : vector(Allocator()) {}</ins>
explicit vector(const Allocator&amp;<del> = Allocator()</del>);
</pre></blockquote>
</li>

<li><p>Change class template <code>map</code> synopsis, 23.4.3.1 <a href="https://wg21.link/map.overview">[map.overview]</a> p2 as indicated:</p>
<blockquote><pre>
<ins>map() : map(Compare()) {}</ins>
explicit map(const Compare&amp; comp<del> = Compare()</del>,
             const Allocator&amp; = Allocator());
</pre></blockquote>
</li>

<li><p>Change 23.4.3.2 <a href="https://wg21.link/map.cons">[map.cons]</a> before p1 as indicated:</p>
<blockquote><pre>
explicit map(const Compare&amp; comp<del> = Compare()</del>,
             const Allocator&amp; = Allocator());
</pre></blockquote>
</li>

<li><p>Change class template <code>multimap</code> synopsis, 23.4.4.1 <a href="https://wg21.link/multimap.overview">[multimap.overview]</a> p2 as indicated:</p>
<blockquote><pre>
<ins>multimap() : multimap(Compare()) {}</ins>
explicit multimap(const Compare&amp; comp<del> = Compare()</del>,
                  const Allocator&amp; = Allocator());
</pre></blockquote>
</li>

<li><p>Change 23.4.4.2 <a href="https://wg21.link/multimap.cons">[multimap.cons]</a> before p1 as indicated:</p>
<blockquote><pre>
explicit multimap(const Compare&amp; comp<del> = Compare()</del>,
                  const Allocator&amp; = Allocator());
</pre></blockquote>
</li>

<li><p>Change class template <code>set</code> synopsis, 23.4.6.1 <a href="https://wg21.link/set.overview">[set.overview]</a> p2 as indicated:</p>
<blockquote><pre>
<ins>set() : set(Compare()) {}</ins>
explicit set(const Compare&amp; comp<del> = Compare()</del>,
             const Allocator&amp; = Allocator());
</pre></blockquote>
</li>

<li><p>Change 23.4.6.2 <a href="https://wg21.link/set.cons">[set.cons]</a> before p1 as indicated:</p>
<blockquote><pre>
explicit set(const Compare&amp; comp<del> = Compare()</del>,
             const Allocator&amp; = Allocator());
</pre></blockquote>
</li>

<li><p>Change class template <code>multiset</code> synopsis, 23.4.7.1 <a href="https://wg21.link/multiset.overview">[multiset.overview]</a> p2 as indicated:</p>
<blockquote><pre>
<ins>multiset() : multiset(Compare()) {}</ins>
explicit multiset(const Compare&amp; comp<del> = Compare()</del>,
                  const Allocator&amp; = Allocator());
</pre></blockquote>
</li>

<li><p>Change 23.4.7.2 <a href="https://wg21.link/multiset.cons">[multiset.cons]</a> before p1 as indicated:</p>
<blockquote><pre>
explicit multiset(const Compare&amp; comp<del> = Compare()</del>,
                  const Allocator&amp; = Allocator());
</pre></blockquote>
</li>

<li><p>Change class template <code>unordered_map</code> synopsis, 23.5.3.1 <a href="https://wg21.link/unord.map.overview">[unord.map.overview]</a> p3 as indicated:</p>
<blockquote><pre>
<ins>unordered_map() : unordered_map(<i>see below</i>) {}</ins>
explicit unordered_map(size_type n<del> = <i>see below</i></del>,
                       const hasher&amp; hf = hasher(),
                       const key_equal&amp; eql = key_equal(),
                       const allocator_type&amp; a = allocator_type());
</pre></blockquote>
</li>

<li><p>Change 23.5.3.2 <a href="https://wg21.link/unord.map.cnstr">[unord.map.cnstr]</a> before p1 as indicated:</p>
<blockquote><pre>
<ins>unordered_map() : unordered_map(<i>see below</i>) {}</ins>
explicit unordered_map(size_type n<del> = <i>see below</i></del>,
                       const hasher&amp; hf = hasher(),
                       const key_equal&amp; eql = key_equal(),
                       const allocator_type&amp; a = allocator_type());
</pre></blockquote>
</li>

<li><p>Change class template <code>unordered_multimap</code> synopsis, 23.5.4.1 <a href="https://wg21.link/unord.multimap.overview">[unord.multimap.overview]</a> p3 as indicated:</p>
<blockquote><pre>
<ins>unordered_multimap() : unordered_multimap(<i>see below</i>) {}</ins>
explicit unordered_multimap(size_type n<del> = <i>see below</i></del>,
                            const hasher&amp; hf = hasher(),
                            const key_equal&amp; eql = key_equal(),
                            const allocator_type&amp; a = allocator_type());
</pre></blockquote>
</li>

<li><p>Change 23.5.4.2 <a href="https://wg21.link/unord.multimap.cnstr">[unord.multimap.cnstr]</a> before p1 as indicated:</p>
<blockquote><pre>
<ins>unordered_multimap() : unordered_multimap(<i>see below</i>) {}</ins>
explicit unordered_multimap(size_type n<del> = <i>see below</i></del>,
                            const hasher&amp; hf = hasher(),
                            const key_equal&amp; eql = key_equal(),
                            const allocator_type&amp; a = allocator_type());
</pre></blockquote>
</li>

<li><p>Change class template <code>unordered_set</code> synopsis, 23.5.6.1 <a href="https://wg21.link/unord.set.overview">[unord.set.overview]</a> p3 as indicated:</p>
<blockquote><pre>
<ins>unordered_set() : unordered_set(<i>see below</i>) {}</ins>
explicit unordered_set(size_type n<del> = <i>see below</i></del>,
                       const hasher&amp; hf = hasher(),
                       const key_equal&amp; eql = key_equal(),
                       const allocator_type&amp; a = allocator_type());
</pre></blockquote>
</li>

<li><p>Change 23.5.6.2 <a href="https://wg21.link/unord.set.cnstr">[unord.set.cnstr]</a> before p1 as indicated:</p>
<blockquote><pre>
<ins>unordered_set() : unordered_set(<i>see below</i>) {}</ins>
explicit unordered_set(size_type n<del> = <i>see below</i></del>,
                       const hasher&amp; hf = hasher(),
                       const key_equal&amp; eql = key_equal(),
                       const allocator_type&amp; a = allocator_type());
</pre></blockquote>
</li>

<li><p>Change class template <code>unordered_multiset</code> synopsis, 23.5.7.1 <a href="https://wg21.link/unord.multiset.overview">[unord.multiset.overview]</a> p3 as indicated:</p>
<blockquote><pre>
<ins>unordered_multiset() : unordered_multiset(<i>see below</i>) {}</ins>
explicit unordered_multiset(size_type n<del> = <i>see below</i></del>,
                            const hasher&amp; hf = hasher(),
                            const key_equal&amp; eql = key_equal(),
                            const allocator_type&amp; a = allocator_type());
</pre></blockquote>
</li>

<li><p>Change 23.5.7.2 <a href="https://wg21.link/unord.multiset.cnstr">[unord.multiset.cnstr]</a> before p1 as indicated:</p>
<blockquote><pre>
<ins>unordered_multiset() : unordered_multiset(<i>see below</i>) {}</ins>
explicit unordered_multiset(size_type n<del> = <i>see below</i></del>,
                            const hasher&amp; hf = hasher(),
                            const key_equal&amp; eql = key_equal(),
                            const allocator_type&amp; a = allocator_type());
</pre></blockquote>
</li>
</ol>

</blockquote>

<p><i>[Issaquah 2014-02-11: Move to Immediate after final review]</i></p>




<p id="res-2193"><b>Proposed resolution:</b></p>
<p>This wording is relative to N3376.</p>

<p>The more general criterion for performing the suggested transformation was: Any type with an initializer-list 
constructor that also has an explicit default constructor.</p>

<ol>
<li><p>Change class template <code>basic_string</code> synopsis, 27.4.3 <a href="https://wg21.link/basic.string">[basic.string]</a> p5 as indicated:</p>
<blockquote><pre>
<ins>basic_string() : basic_string(Allocator()) { }</ins>
explicit basic_string(const Allocator&amp; a<del> = Allocator()</del>);
</pre></blockquote>
</li>

<li><p>Change 27.4.3.3 <a href="https://wg21.link/string.cons">[string.cons]</a> before p1 as indicated:</p>
<blockquote><pre>
explicit basic_string(const Allocator&amp; a<del> = Allocator()</del>);
</pre></blockquote>
</li>

<li><p>Change class template <code>deque</code> synopsis, 23.3.5.1 <a href="https://wg21.link/deque.overview">[deque.overview]</a> p2 as indicated:</p>
<blockquote><pre>
<ins>deque() : deque(Allocator()) { }</ins>
explicit deque(const Allocator&amp;<del> = Allocator()</del>);
</pre></blockquote>
</li>

<li><p>Change 23.3.5.2 <a href="https://wg21.link/deque.cons">[deque.cons]</a> before p1 as indicated:</p>
<blockquote><pre>
explicit deque(const Allocator&amp;<del> = Allocator()</del>);
</pre></blockquote>
</li>

<li><p>Change class template <code>forward_list</code> synopsis,  [forwardlist.overview] p3 as indicated:</p>
<blockquote><pre>
<ins>forward_list() : forward_list(Allocator()) { }</ins>
explicit forward_list(const Allocator&amp;<del> = Allocator()</del>);
</pre></blockquote>
</li>

<li><p>Change  [forwardlist.cons] before p1 as indicated:</p>
<blockquote><pre>
explicit forward_list(const Allocator&amp;<del> = Allocator()</del>);
</pre></blockquote>
</li>

<li><p>Change class template <code>list</code> synopsis, 23.3.11.1 <a href="https://wg21.link/list.overview">[list.overview]</a> p2 as indicated:</p>
<blockquote><pre>
<ins>list() : list(Allocator()) { }</ins>
explicit list(const Allocator&amp;<del> = Allocator()</del>);
</pre></blockquote>
</li>

<li><p>Change 23.3.11.2 <a href="https://wg21.link/list.cons">[list.cons]</a> before p1 as indicated:</p>
<blockquote><pre>
explicit list(const Allocator&amp;<del> = Allocator()</del>);
</pre></blockquote>
</li>

<li><p>Change class template <code>vector</code> synopsis, 23.3.13.1 <a href="https://wg21.link/vector.overview">[vector.overview]</a> p2 as indicated:</p>
<blockquote><pre>
<ins>vector() : vector(Allocator()) { }</ins>
explicit vector(const Allocator&amp;<del> = Allocator()</del>);
</pre></blockquote>
</li>

<li><p>Change 23.3.13.2 <a href="https://wg21.link/vector.cons">[vector.cons]</a> before p1 as indicated:</p>
<blockquote><pre>
explicit vector(const Allocator&amp;<del> = Allocator()</del>);
</pre></blockquote>
</li>

<li><p>Change class template specialization <code>vector&lt;bool&gt;</code> synopsis, 23.3.14 <a href="https://wg21.link/vector.bool">[vector.bool]</a> p1 as indicated:</p>
<blockquote><pre>
<ins>vector() : vector(Allocator()) { }</ins>
explicit vector(const Allocator&amp;<del> = Allocator()</del>);
</pre></blockquote>
</li>

<li><p>Change class template <code>map</code> synopsis, 23.4.3.1 <a href="https://wg21.link/map.overview">[map.overview]</a> p2 as indicated:</p>
<blockquote><pre>
<ins>map() : map(Compare()) { }</ins>
explicit map(const Compare&amp; comp<del> = Compare()</del>,
             const Allocator&amp; = Allocator());
</pre></blockquote>
</li>

<li><p>Change 23.4.3.2 <a href="https://wg21.link/map.cons">[map.cons]</a> before p1 as indicated:</p>
<blockquote><pre>
explicit map(const Compare&amp; comp<del> = Compare()</del>,
             const Allocator&amp; = Allocator());
</pre></blockquote>
</li>

<li><p>Change class template <code>multimap</code> synopsis, 23.4.4.1 <a href="https://wg21.link/multimap.overview">[multimap.overview]</a> p2 as indicated:</p>
<blockquote><pre>
<ins>multimap() : multimap(Compare()) { }</ins>
explicit multimap(const Compare&amp; comp<del> = Compare()</del>,
                  const Allocator&amp; = Allocator());
</pre></blockquote>
</li>

<li><p>Change 23.4.4.2 <a href="https://wg21.link/multimap.cons">[multimap.cons]</a> before p1 as indicated:</p>
<blockquote><pre>
explicit multimap(const Compare&amp; comp<del> = Compare()</del>,
                  const Allocator&amp; = Allocator());
</pre></blockquote>
</li>

<li><p>Change class template <code>set</code> synopsis, 23.4.6.1 <a href="https://wg21.link/set.overview">[set.overview]</a> p2 as indicated:</p>
<blockquote><pre>
<ins>set() : set(Compare()) { }</ins>
explicit set(const Compare&amp; comp<del> = Compare()</del>,
             const Allocator&amp; = Allocator());
</pre></blockquote>
</li>

<li><p>Change 23.4.6.2 <a href="https://wg21.link/set.cons">[set.cons]</a> before p1 as indicated:</p>
<blockquote><pre>
explicit set(const Compare&amp; comp<del> = Compare()</del>,
             const Allocator&amp; = Allocator());
</pre></blockquote>
</li>

<li><p>Change class template <code>multiset</code> synopsis, 23.4.7.1 <a href="https://wg21.link/multiset.overview">[multiset.overview]</a> p2 as indicated:</p>
<blockquote><pre>
<ins>multiset() : multiset(Compare()) { }</ins>
explicit multiset(const Compare&amp; comp<del> = Compare()</del>,
                  const Allocator&amp; = Allocator());
</pre></blockquote>
</li>

<li><p>Change 23.4.7.2 <a href="https://wg21.link/multiset.cons">[multiset.cons]</a> before p1 as indicated:</p>
<blockquote><pre>
explicit multiset(const Compare&amp; comp<del> = Compare()</del>,
                  const Allocator&amp; = Allocator());
</pre></blockquote>
</li>

<li><p>Change class template <code>unordered_map</code> synopsis, 23.5.3.1 <a href="https://wg21.link/unord.map.overview">[unord.map.overview]</a> p3 as indicated:</p>
<blockquote><pre>
<ins>unordered_map();</ins>
explicit unordered_map(size_type n<del> = <i>see below</i></del>,
                       const hasher&amp; hf = hasher(),
                       const key_equal&amp; eql = key_equal(),
                       const allocator_type&amp; a = allocator_type());
</pre></blockquote>
</li>

<li><p>Change 23.5.3.2 <a href="https://wg21.link/unord.map.cnstr">[unord.map.cnstr]</a> before p1 as indicated:</p>
<blockquote><pre>
<ins>unordered_map() : unordered_map(size_type(<i>see below</i>)) { }</ins>
explicit unordered_map(size_type n<del> = <i>see below</i></del>,
                       const hasher&amp; hf = hasher(),
                       const key_equal&amp; eql = key_equal(),
                       const allocator_type&amp; a = allocator_type());
</pre>

-1- <i>Effects:</i> Constructs an empty <code>unordered_map</code> using the specified hash function, key equality func-<br />
tion, and allocator, and using at least <i>n</i> buckets. <del>If <i>n</i> is not provided,</del> <ins>For the default constructor</ins><br />
the number of buckets is implementation-defined. <code>max_load_factor()</code> returns 1.0.
</blockquote>

</li>

<li><p>Change class template <code>unordered_multimap</code> synopsis, 23.5.4.1 <a href="https://wg21.link/unord.multimap.overview">[unord.multimap.overview]</a> p3 as indicated:</p>
<blockquote><pre>
<ins>unordered_multimap();</ins>
explicit unordered_multimap(size_type n<del> = <i>see below</i></del>,
                            const hasher&amp; hf = hasher(),
                            const key_equal&amp; eql = key_equal(),
                            const allocator_type&amp; a = allocator_type());
</pre></blockquote>
</li>

<li><p>Change 23.5.4.2 <a href="https://wg21.link/unord.multimap.cnstr">[unord.multimap.cnstr]</a> before p1 as indicated:</p>
<blockquote><pre>
<ins>unordered_multimap() : unordered_multimap(size_type(<i>see below</i>)) { }</ins>
explicit unordered_multimap(size_type n<del> = <i>see below</i></del>,
                            const hasher&amp; hf = hasher(),
                            const key_equal&amp; eql = key_equal(),
                            const allocator_type&amp; a = allocator_type());
</pre>

-1- <i>Effects:</i> Constructs an empty <code>unordered_multimap</code> using the specified hash function, key equality<br />
function, and allocator, and using at least <i>n</i> buckets. <del>If <i>n</i> is not provided,</del> <ins>For the default constructor</ins><br />
the number of buckets is implementation-defined. <code>max_load_factor()</code> returns 1.0.

</blockquote>
</li>

<li><p>Change class template <code>unordered_set</code> synopsis, 23.5.6.1 <a href="https://wg21.link/unord.set.overview">[unord.set.overview]</a> p3 as indicated:</p>
<blockquote><pre>
<ins>unordered_set();</ins>
explicit unordered_set(size_type n<del> = <i>see below</i></del>,
                       const hasher&amp; hf = hasher(),
                       const key_equal&amp; eql = key_equal(),
                       const allocator_type&amp; a = allocator_type());
</pre></blockquote>
</li>

<li><p>Change 23.5.6.2 <a href="https://wg21.link/unord.set.cnstr">[unord.set.cnstr]</a> before p1 as indicated:</p>
<blockquote><pre>
<ins>unordered_set() : unordered_set(size_type(<i>see below</i>)) { }</ins>
explicit unordered_set(size_type n<del> = <i>see below</i></del>,
                       const hasher&amp; hf = hasher(),
                       const key_equal&amp; eql = key_equal(),
                       const allocator_type&amp; a = allocator_type());
</pre>

-1- <i>Effects:</i> Constructs an empty <code>unordered_set</code> using the specified hash function, key equality func-<br />
tion, and allocator, and using at least <i>n</i> buckets. <del>If <i>n</i> is not provided,</del> <ins>For the default constructor</ins><br />
the number of buckets is implementation-defined. <code>max_load_factor()</code> returns 1.0.

</blockquote>
</li>

<li><p>Change class template <code>unordered_multiset</code> synopsis, 23.5.7.1 <a href="https://wg21.link/unord.multiset.overview">[unord.multiset.overview]</a> p3 as indicated:</p>
<blockquote><pre>
<ins>unordered_multiset();</ins>
explicit unordered_multiset(size_type n<del> = <i>see below</i></del>,
                            const hasher&amp; hf = hasher(),
                            const key_equal&amp; eql = key_equal(),
                            const allocator_type&amp; a = allocator_type());
</pre></blockquote>
</li>

<li><p>Change 23.5.7.2 <a href="https://wg21.link/unord.multiset.cnstr">[unord.multiset.cnstr]</a> before p1 as indicated:</p>
<blockquote><pre>
<ins>unordered_multiset() : unordered_multiset(size_type(<i>see below</i>)) { }</ins>
explicit unordered_multiset(size_type n<del> = <i>see below</i></del>,
                            const hasher&amp; hf = hasher(),
                            const key_equal&amp; eql = key_equal(),
                            const allocator_type&amp; a = allocator_type());
</pre>

-1- <i>Effects:</i> Constructs an empty <code>unordered_multiset</code> using the specified hash function, key equality<br />
function, and allocator, and using at least <i>n</i> buckets. <del>If <i>n</i> is not provided,</del> <ins>For the default constructor</ins><br />
the number of buckets is implementation-defined. <code>max_load_factor()</code> returns 1.0.

</blockquote>
</li>
</ol>






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