New issue from Dietmar Kühl: task's stop source is always created

Author: dietmarkuehl

xml/issue4347.xml

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+<?xml version='1.0' encoding='utf-8' standalone='no'?>
+<!DOCTYPE issue SYSTEM "lwg-issue.dtd">
+
+<issue num="4347" status="New">
+<title><code>task</code>'s stop source is always created</title>
+<section><sref ref="[task.promise]"/></section>
+<submitter>Dietmar Kühl</submitter>
+<date>01 Sep 2025</date>
+<priority>99</priority>
+
+<discussion>
+<p>
+The type <code>task&lt;...&gt;::promise_type</code> has exposition-only
+members <code><i>source</i></code> and <code><i>token</i></code>.
+These can be interpreted as always existing which would be a
+performance issue for former and an unnecessary constraints for the
+latter (because stop tokens aren't required to be default constructible).
+</p>
+<p>
+The intent is that the stop token obtained from the
+<code>get_stop_token</code> query of the receiver's environment is
+used. Only if this type is different from the <code>task</code>'s
+<code>stop_token_type</code> a stop source of type
+<code>stop_source_type</code> needs to be created when the
+<code>get_stop_token</code> query is used on the promise type's
+environment. The stop token doesn't need to be stored at all: it
+can either be obtained from the receiver's environment or from the
+stop source. The fix is to show the stop source as an optionally
+present member of of the operation state and it should be of type
+<code>std::optional&lt;stop_source_type&gt;</code> to imply that
+it is only created when accessed.
+</p>
+</discussion>
+
+<resolution>
+<p>
+</p>
+</resolution>
+
+</issue>