issue4345.xml

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<issue num="4345" status="New">
<title><code>task::promise_type::return_value</code> default template parameter</title>
<section><sref ref="[task.promise]"/></section>
<submitter>Dietmar Kühl</submitter>
<date>01 Sep 2025</date>
<priority>99</priority>

<discussion>
<p>
The template parameter <code>V</code> of
<code>task::promise_type::return_value</code> doesn't have a default
template argument specified. Specifying a default template argument of <code>T</code>
would enable use of <code>co_return { ... }</code> which would be
consistent with normal <code>return</code> statements. This feature
was not discussed in the design paper but based on the LEWG discussion
on 2025-08-26 it is considered to be more a bug fix than a new feature.
</p>
</discussion>

<resolution>
<p>
Add a default template argument of <code>T</code> to the template
parameter <code>V</code> of <code>task::promise_type::return_value</code>
in the synopsis of <a href="https://wg21.link/task.promise">[task.promise]</a>:
<blockquote><pre>
namespace std::execution {
  template&lt;class T, class Environment&gt;
  class task&lt;T, Environment&gt;::promise_type {
     ...
    template&lt;typename V <ins>= T</ins>&gt;
    void return_value(V&amp;&amp; value);
    ...
  };

}
</pre></blockquote>
</p>
</resolution>

</issue>