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<title>Issue 265: std::pair::pair() effects overly restrictive</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#CD1">CD1</a> status.</em></p>
<h3 id="265"><a href="lwg-defects.html#265">265</a>. std::pair::pair() effects overly restrictive</h3>
<p><b>Section:</b> 22.3 <a href="https://wg21.link/pairs">[pairs]</a> <b>Status:</b> <a href="lwg-active.html#CD1">CD1</a>
 <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2000-09-11 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#pairs">issues</a> in [pairs].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#CD1">CD1</a> status.</p>
<p><b>Discussion:</b></p>
<p>
I don't see any requirements on the types of the elements of the
std::pair container in 20.2.2. From the descriptions of the member
functions it appears that they must at least satisfy the requirements of
20.1.3 [lib.copyconstructible] and 20.1.4 [lib.default.con.req], and in
the case of the [in]equality operators also the requirements of 20.1.1
[lib.equalitycomparable] and 20.1.2 [lib.lessthancomparable].
</p>

<p>
I believe that the the CopyConstructible requirement is unnecessary in
the case of 20.2.2, p2.
</p>


<p id="res-265"><b>Proposed resolution:</b></p>
<p>Change the Effects clause in 20.2.2, p2 from</p>

<blockquote><p>
-2- <b>Effects</b>: Initializes its members as if implemented: <code> pair() :
first(T1()), second(T2()) {} </code>
</p></blockquote>

<p>to</p>

<blockquote><p>
-2- <b>Effects</b>: Initializes its members as if implemented: <code> pair() :
first(), second() {} </code>
</p></blockquote>


<p><b>Rationale:</b></p>
<p>The existing specification of pair's constructor appears to be a
historical artifact: there was concern that pair's members be properly
zero-initialized when they are built-in types.  At one time there was
uncertainty about whether they would be zero-initialized if the
default constructor was written the obvious way.  This has been
clarified by core issue 178, and there is no longer any doubt that
the straightforward implementation is correct.</p>




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