New issue from Jiang An: "Constants in std::regex_constants should be…

… allowed to be enumerators"

xml/issue3998.xml

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+<?xml version='1.0' encoding='utf-8' standalone='no'?>
+<!DOCTYPE issue SYSTEM "lwg-issue.dtd">
+
+<issue num="3998" status="New">
+<title>Constants in <tt>std::regex_constants</tt> should be allowed to be enumerators</title>
+<section><sref ref="[re.const]"/></section>
+<submitter>Jiang An</submitter>
+<date>18 Oct 2023</date>
+<priority>99</priority>
+
+<discussion>
+<p>
+Currently, MSVC STL and libc++ implement constants in <tt>std::regex_constants</tt> as 
+enumerators of unscoped enumerations, while the standard specify them to be <tt>constexpr</tt> variables.
+<p/>
+<a href="https://github.com/microsoft/STL/issues/4100#issuecomment-1767717721">Casey Carter argued</a> 
+that it would be better to make these constants prvalues to avoid wasting space in object files. And 
+presumably almost all users just use their values without odr-using them or relying on their value category.
+<p/>
+Perhaps we should allow these constants to be enumerators of the corresponding type (<tt>syntax_option_type</tt>, 
+<tt>match_flag_type</tt>, or <tt>error_type</tt>) if the corresponding type is an enumeration.
+<p/>
+Notes: since C++20, we can even make the enumeration types scoped and expose the enumerators to the 
+namespace by using-declaration or using-enum-declaration. <paper num="P0439R0"/> might be related, 
+since it changed former enumerators to <tt>constexpr</tt> variables.
+</p>
+</discussion>
+
+<resolution>
+</resolution>
+
+</issue>