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    CWG Issue 2943</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="2943"></A><H4>2943.
  
Discarding a void return value
</H4>
<B>Section: </B>9.13.9&#160; [<A href="https://wg21.link/dcl.attr.nodiscard">dcl.attr.nodiscard</A>]
 &#160;&#160;&#160;

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

 <B>Submitter: </B>Brian Bi
 &#160;&#160;&#160;

 <B>Date: </B>2024-10-24<BR>


<P>[Accepted as a DR at the February, 2025 meeting.]</P>

<P>(From submission
<A HREF="https://github.com/cplusplus/CWG/issues/628">#628</A>.)
</P>

<P>A warning is currently, but ought not to be, encouraged for a call
to a [[nodiscard]] function with a void return type.  Such a situation
may arise for dependent return types.  For example:</P>

<PRE>
  [[nodiscard]] void f();
  template&lt;class T&gt; [[nodiscard]] T g();

  void h() {
    f();                //<SPAN CLASS="cmnt"> suggested change: warning no longer recommended</SPAN>
    (void)f();          //<SPAN CLASS="cmnt"> warning not recommended</SPAN>
    g&lt;int&gt;();           //<SPAN CLASS="cmnt"> warning recommended</SPAN>
    g&lt;void&gt;();          //<SPAN CLASS="cmnt"> suggested change: warning no longer recommended</SPAN>
    (void)g&lt;void&gt;();    //<SPAN CLASS="cmnt"> warning not recommended</SPAN>
  }
</PRE>

<P><B>Proposed resolution (2025-01-21, approved by CWG 2025-02-14):</B></P>

<P>Change in 9.13.9 [<A href="https://wg21.link/dcl.attr.nodiscard#4">dcl.attr.nodiscard</A>] paragraph 4 as follows:</P>

<BLOCKQUOTE>

Recommended practice: Appearance of a nodiscard call as a
potentially-evaluated discarded-value expression
(7.2 [<A href="https://wg21.link/expr.prop">expr.prop</A>]) <INS>of non-void type</INS> is discouraged
unless explicitly cast to void. Implementations should issue a warning
in such cases.  The value of a <I>has-attribute-expression</I> for the
nodiscard attribute should be 0 unless the implementation can issue
such warnings.

</BLOCKQUOTE>

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