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2431. Missing regular expression traits requirements

Section: 30.2 [re.req] Status: New Submitter: Jonathan Wakely Opened: 2014-09-30 Last modified: 2020-04-18

Priority: 3

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Discussion:

The requirements on the traits class in 30.2 [re.req] do not say whether a regular expression traits class is required to be DefaultConstructible, CopyConstructible, CopyAssignable etc.

The std::regex_traits class appears to be all of the above, but can basic_regex assume that for user-defined traits classes?

Should the following statements all leave u in equivalent states?

X u{v};
X u; u = v;
X u; u.imbue(v.getloc();

Whether they are equivalent has implications for basic_regex copy construction and assignment.

[2020-04-16, Jonathan adds that 30.7.5 [re.regex.locale] requires the traits type to be default-initialized, despite no guarantee that the traits type is default constructible. ]

Proposed resolution: