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    CWG Issue 2780</TITLE>
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<P><EM>This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21
  Core Issues List revision 118b.
  See http://www.open-std.org/jtc1/sc22/wg21/ for the official
  list.</EM></P>
<P>2025-09-28</P>
<HR>
<A NAME="2780"></A><H4>2780.
  
<TT>reinterpret_cast</TT> to reference to function types
</H4>
<B>Section: </B>7.6.1.10&#160; [<A href="https://wg21.link/expr.reinterpret.cast">expr.reinterpret.cast</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD7
 &#160;&#160;&#160;

 <B>Submitter: </B>Lauri Vasama
 &#160;&#160;&#160;

 <B>Date: </B>2023-08-07<BR>


<P>[Accepted as a DR at the November, 2023 meeting.]</P>

<P>Subclause 7.6.1.10 [<A href="https://wg21.link/expr.reinterpret.cast#11">expr.reinterpret.cast</A>] paragraph 11 specifies:</P>

<BLOCKQUOTE>

A glvalue of type T1, designating an object x, can be cast to the type
&#8220;reference to T2&#8221; if an expression of type &#8220;pointer
to T1&#8221; can be explicitly converted to the type &#8220;pointer to
T2&#8221; using a reinterpret_cast.  The result is that of
*reinterpret_cast&lt;T2 *&gt;(p) where p is a pointer to x of type
&#8220;pointer to T1&#8221;. No temporary is created, no copy is made,
and no constructors (11.4.5 [<A href="https://wg21.link/class.ctor">class.ctor</A>]) or conversion
functions (11.4.8 [<A href="https://wg21.link/class.conv">class.conv</A>]) are called. [ Footnote: ... ]

</BLOCKQUOTE>

<P>The wording does not cover references to function type, only
references to object types.  All major implementations accept the
following example:</P>

<PRE>
  void f() {}

  void(&amp;g())(int) {
    return reinterpret_cast&lt;void(&amp;)(int)&gt;(f);
  }
</PRE>

<P><B>Proposed resolution (approved by CWG 2023-09-15):</B></P>

<P>Change in 7.6.1.10 [<A href="https://wg21.link/expr.reinterpret.cast#11">expr.reinterpret.cast</A>] paragraph 11 as follows:</P>

<BLOCKQUOTE>

A glvalue of type T1, designating
an object <INS>or function</INS> x, can be cast to the type
&#8220;reference to T2&#8221; if an expression of type &#8220;pointer
to T1&#8221; can be explicitly converted to the type &#8220;pointer to
T2&#8221; using a <TT>reinterpret_cast</TT>.  The result is that of
<TT>*reinterpret_cast&lt;T2 *&gt;(p)</TT> where <TT>p</TT> is a
pointer to x of type &#8220;pointer to T1&#8221;. No temporary is
created, no copy is made, and no constructors
(11.4.5 [<A href="https://wg21.link/class.ctor">class.ctor</A>]) or conversion functions
(11.4.8 [<A href="https://wg21.link/class.conv">class.conv</A>]) are called. [ Footnote: ... ]

</BLOCKQUOTE>

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