This patch attempts to solve an issue in basic_string after adding string_view to several functions that came in during incomplete patch of LWG 2758/LWG 2946, in short: Functions that take a string_view parameter value are now replaced by constrained templates taking const T& that is convertible to string_view. The patch also attempts to complete the LWG 2946 P/R. With the absence of the std::is_nothrow_convertible traits, the P/R also restores some of the lost noexcept specifications of const functions (find, compare, etc) by conditional noexcept simply comparing whether T is the same type as string_view.
During that fix two related, minor problems where found and also fixed: a) Member int compare(basic_string_view<charT, traits> sv) const; should be noexcept according the spec, but this function wasn't at all. Since the changes for LWG 2946 required me to touch the noexcept specifier anyway I replaced it by the conditional noexcept mentioned above. I do not know what the general policy for "narrow contract" functions is in libstdc++ code, I therefore didn't touch the also missing (but optional) noexcept for int compare(size_type pos1, size_type n1,basic_string_view<charT, traits> sv) const; template<class T> int compare(size_type pos1, size_type n1, const T& t, size_type pos2, size_type n2 = npos) const; If wanted, I can apply the same conditional noexcept here as well. b) Two constructors using the const T& -> string_view conversion did this via explicit conversion instead of implicit conversion. This difference can be observed by user-code and in certain cases either a well-formed program can become ill-formed or may perform different runtime behaviour (Overloaded conversion operators, one explicit, the other implicit). This patch is *untested*, because I cannot make the tests run on my Windows system. Thanks, - Daniel
ChangeLog_79162.patch
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79162.patch
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