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<title>Issue 3338: Rename default_constructible to default_initializable</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++20">C++20</a> status.</em></p>
<h3 id="3338"><a href="lwg-defects.html#3338">3338</a>. Rename <code>default_constructible</code> to <code>default_initializable</code></h3>
<p><b>Section:</b> 18.4.12 <a href="https://wg21.link/concept.default.init">[concept.default.init]</a> <b>Status:</b> <a href="lwg-active.html#C++20">C++20</a>
 <b>Submitter:</b> Casey Carter <b>Opened:</b> 2019-11-18 <b>Last modified:</b> 2021-06-06</p>
<p><b>Priority: </b>0
</p>
<p><b>View all other</b> <a href="lwg-index.html#concept.default.init">issues</a> in [concept.default.init].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++20">C++20</a> status.</p>
<p><b>Discussion:</b></p>
<p>
WG21 merged <a href="https://wg21.link/p1754r1">P1754R1</a> "Rename concepts to <code>standard_case</code> for C++20"
into the working draft as LWG Motion 11 in 2019 Cologne. That proposal contains editorial instructions to
rename what was the <code>DefaultConstructible</code> concept:
</p>
<blockquote style="border-left: 3px solid #ccc;padding-left: 15px;">
<pre>
IF LWG3151 ACCEPTED:
  default_initializable
ELSE
  default_constructible
</pre>
</blockquote>
<p>
Notably LWG <a href="lwg-defects.html#3151" title="ConvertibleTo rejects conversions from array and function types (Status: Resolved)">3151</a><sup><a href="https://cplusplus.github.io/LWG/issue3151" title="Latest snapshot">(i)</a></sup> "<code>ConvertibleTo</code> rejects conversions from array and function types" is
not the intended issue number, LWG <a href="lwg-defects.html#3149" title="DefaultConstructible should require default initialization (Status: C++20)">3149</a><sup><a href="https://cplusplus.github.io/LWG/issue3149" title="Latest snapshot">(i)</a></sup> "<code>DefaultConstructible</code> should require default
initialization" is. It was made clear during discussion in LEWG that 3149 would change the concept to require default-initialization to be valid rather than value-initialization which the <code>is_default_constructible</code>
trait requires. LEWG agreed that it would be confusing to have a trait and concept with very similar names
yet slightly different meanings, and approved <a href="https://wg21.link/p1754r1">P1754R1</a>'s proposed renaming.
<p/>
LWG <a href="lwg-defects.html#3149" title="DefaultConstructible should require default initialization (Status: C++20)">3149</a><sup><a href="https://cplusplus.github.io/LWG/issue3149" title="Latest snapshot">(i)</a></sup> was moved to "Ready" but not approved by WG21 until Belfast &mdash; after the application
of P1754R1 to the working draft &mdash; so this renaming has not happened, but the rationale remains valid.
</p>

<p><i>[2019-11-30 Issue Prioritization]</i></p>

<p>Status to Tentatively Ready and priority to 0 after eight positive votes on the reflector.</p>


<p id="res-3338"><b>Proposed resolution:</b></p>
<p>This wording is relative to <a href="https://wg21.link/n4835">N4835</a>.</p>

<ol>
<li><p>Change the stable name "[concept.defaultconstructible]" to "[concept.default.init]" and retitle
"Concept <code>default_constructible</code>" to "Concept <code>default_initializable</code>". Replace all references
to the name <code>default_constructible</code> with <code>default_initializable</code> (There are 20 occurrences).</p>
</li>
</ol>




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